Remove converting user error to GIT_EUSER

This changes the behavior of callbacks so that the callback error
code is not converted into GIT_EUSER and instead we propagate the
return value through to the caller.  Instead of using the
giterr_capture and giterr_restore functions, we now rely on all
functions to pass back the return value from a callback.

To avoid having a return value with no error message, the user
can call the public giterr_set_str or some such function to set
an error message.  There is a new helper 'giterr_set_callback'
that functions can invoke after making a callback which ensures
that some error message was set in case the callback did not set
one.

In places where the sign of the callback return value is
meaningful (e.g. positive to skip, negative to abort), only the
negative values are returned back to the caller, obviously, since
the other values allow for continuing the loop.

The hardest parts of this were in the checkout code where positive
return values were overloaded as meaningful values for checkout.
I fixed this by adding an output parameter to many of the internal
checkout functions and removing the overload.  This added some
code, but it is probably a better implementation.

There is some funkiness in the network code where user provided
callbacks could be returning a positive or a negative value and
we want to rely on that to cancel the loop.  There are still a
couple places where an user error might get turned into GIT_EUSER
there, I think, though none exercised by the tests.

57 files changed, 603 insertions, 804 deletions

diff --git a/include/git2/config.h b/include/git2/config.h
index 95da4bc03..3ab58f1a7 100644
--- a/include/git2/config.h
+++ b/include/git2/config.h
@@ -612,8 +612,8 @@ GIT_EXTERN(int) git_config_parse_int64(int64_t *out, const char *value);
 GIT_EXTERN(int) git_config_backend_foreach_match(
 	git_config_backend *backend,
 	const char *regexp,
-	int (*fn)(const git_config_entry *, void *),
-	void *data);
+	git_config_foreach_cb callback,
+	void *payload);
 
 
 /** @} */
diff --git a/include/git2/errors.h b/include/git2/errors.h
index c6076f3ab..26f9a747c 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -71,6 +71,7 @@ typedef enum {
 	GITERR_SSH,
 	GITERR_FILTER,
 	GITERR_REVERT,
+	GITERR_CALLBACK,
 } git_error_t;
 
 /**
diff --git a/src/attr.c b/src/attr.c
index 1a0f1f97f..08d7ee99d 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -191,11 +191,10 @@ int git_attr_foreach(
 				if (error < 0)
 					goto cleanup;
 
-				error = callback(assign->name, assign->value, payload);
-				if (error) {
-					error = giterr_user_cancel();
+				error = GITERR_CALLBACK(
+					callback(assign->name, assign->value, payload) );
+				if (error)
 					goto cleanup;
-				}
 			}
 		}
 	}
@@ -480,7 +479,6 @@ typedef struct {
 	const char *workdir;
 	git_index *index;
 	git_vector *files;
-	git_error_state error;
 } attr_walk_up_info;
 
 int git_attr_cache__decide_sources(
@@ -524,7 +522,7 @@ static int push_one_attr(void *ref, git_buf *path)
 			info->repo, path->ptr, GIT_ATTR_FILE, src[i],
 			git_attr_file__parse_buffer, NULL, info->files);
 
-	return giterr_capture(&info->error, error);
+	return error;
 }
 
 static int collect_attr_files(
@@ -570,8 +568,6 @@ static int collect_attr_files(
 	info.files = files;
 
 	error = git_path_walk_up(&dir, workdir, push_one_attr, &info);
-	if (error == GIT_EUSER)
-		error = giterr_restore(&info.error);
 	if (error < 0)
 		goto cleanup;
 
diff --git a/src/checkout.c b/src/checkout.c
index e33ac2ed6..4c64252e4 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -83,10 +83,8 @@ static int checkout_notify(
 	const git_diff_file *baseline = NULL, *target = NULL, *workdir = NULL;
 	const char *path = NULL;
 
-	if (!data->opts.notify_cb)
-		return 0;
-
-	if ((why & data->opts.notify_flags) == 0)
+	if (!data->opts.notify_cb ||
+		(why & data->opts.notify_flags) == 0)
 		return 0;
 
 	if (wditem) {
@@ -125,8 +123,10 @@ static int checkout_notify(
 		path = delta->old_file.path;
 	}
 
-	return data->opts.notify_cb(
-		why, path, baseline, target, workdir, data->opts.notify_payload);
+	return giterr_set_callback(
+		data->opts.notify_cb(
+			why, path, baseline, target, workdir, data->opts.notify_payload),
+		"git_checkout notification");
 }
 
 static bool checkout_is_workdir_modified(
@@ -186,69 +186,66 @@ static bool checkout_is_workdir_modified(
 	((data->strategy & GIT_CHECKOUT_##FLAG) ? CHECKOUT_ACTION__##YES : CHECKOUT_ACTION__##NO)
 
 static int checkout_action_common(
+	int *action,
 	checkout_data *data,
-	int action,
 	const git_diff_delta *delta,
 	const git_index_entry *wd)
 {
 	git_checkout_notify_t notify = GIT_CHECKOUT_NOTIFY_NONE;
 
-	if (action <= 0)
-		return action;
-
 	if ((data->strategy & GIT_CHECKOUT_UPDATE_ONLY) != 0)
-		action = (action & ~CHECKOUT_ACTION__REMOVE);
+		*action = (*action & ~CHECKOUT_ACTION__REMOVE);
 
-	if ((action & CHECKOUT_ACTION__UPDATE_BLOB) != 0) {
+	if ((*action & CHECKOUT_ACTION__UPDATE_BLOB) != 0) {
 		if (S_ISGITLINK(delta->new_file.mode))
-			action = (action & ~CHECKOUT_ACTION__UPDATE_BLOB) |
+			*action = (*action & ~CHECKOUT_ACTION__UPDATE_BLOB) |
 				CHECKOUT_ACTION__UPDATE_SUBMODULE;
 
 		/* to "update" a symlink, we must remove the old one first */
 		if (delta->new_file.mode == GIT_FILEMODE_LINK && wd != NULL)
-			action |= CHECKOUT_ACTION__REMOVE;
+			*action |= CHECKOUT_ACTION__REMOVE;
 
 		notify = GIT_CHECKOUT_NOTIFY_UPDATED;
 	}
 
-	if ((action & CHECKOUT_ACTION__CONFLICT) != 0)
+	if ((*action & CHECKOUT_ACTION__CONFLICT) != 0)
 		notify = GIT_CHECKOUT_NOTIFY_CONFLICT;
 
-	if (notify != GIT_CHECKOUT_NOTIFY_NONE &&
-		checkout_notify(data, notify, delta, wd) != 0)
-		return giterr_user_cancel();
-
-	return action;
+	return checkout_notify(data, notify, delta, wd);
 }
 
 static int checkout_action_no_wd(
+	int *action,
 	checkout_data *data,
 	const git_diff_delta *delta)
 {
-	int action = CHECKOUT_ACTION__NONE;
+	int error = 0;
+
+	*action = CHECKOUT_ACTION__NONE;
 
 	switch (delta->status) {
 	case GIT_DELTA_UNMODIFIED: /* case 12 */
-		if (checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, NULL))
-			return giterr_user_cancel();
-		action = CHECKOUT_ACTION_IF(SAFE_CREATE, UPDATE_BLOB, NONE);
+		error = checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, NULL);
+		if (error)
+			return error;
+		*action = CHECKOUT_ACTION_IF(SAFE_CREATE, UPDATE_BLOB, NONE);
 		break;
 	case GIT_DELTA_ADDED:    /* case 2 or 28 (and 5 but not really) */
-		action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+		*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
 		break;
 	case GIT_DELTA_MODIFIED: /* case 13 (and 35 but not really) */
-		action = CHECKOUT_ACTION_IF(SAFE_CREATE, UPDATE_BLOB, CONFLICT);
+		*action = CHECKOUT_ACTION_IF(SAFE_CREATE, UPDATE_BLOB, CONFLICT);
 		break;
 	case GIT_DELTA_TYPECHANGE: /* case 21 (B->T) and 28 (T->B)*/
 		if (delta->new_file.mode == GIT_FILEMODE_TREE)
-			action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+			*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
 		break;
 	case GIT_DELTA_DELETED: /* case 8 or 25 */
 	default: /* impossible */
 		break;
 	}
 
-	return checkout_action_common(data, action, delta, NULL);
+	return checkout_action_common(action, data, delta, NULL);
 }
 
 static int checkout_action_wd_only(
@@ -257,6 +254,7 @@ static int checkout_action_wd_only(
 	const git_index_entry *wd,
 	git_vector *pathspec)
 {
+	int error = 0;
 	bool remove = false;
 	git_checkout_notify_t notify = GIT_CHECKOUT_NOTIFY_NONE;
 
@@ -269,13 +267,13 @@ static int checkout_action_wd_only(
 	/* check if item is tracked in the index but not in the checkout diff */
 	if (data->index != NULL) {
 		if (wd->mode != GIT_FILEMODE_TREE) {
-			int error;
-
-			if ((error = git_index_find(NULL, data->index, wd->path)) == 0) {
+			if (!(error = git_index_find(NULL, data->index, wd->path))) {
 				notify = GIT_CHECKOUT_NOTIFY_DIRTY;
 				remove = ((data->strategy & GIT_CHECKOUT_FORCE) != 0);
 			} else if (error != GIT_ENOTFOUND)
 				return error;
+			else
+				giterr_clear();
 		} else {
 			/* for tree entries, we have to see if there are any index
 			 * entries that are contained inside that tree
@@ -301,18 +299,16 @@ static int checkout_action_wd_only(
 		remove = ((data->strategy & GIT_CHECKOUT_REMOVE_UNTRACKED) != 0);
 	}
 
-	if (checkout_notify(data, notify, NULL, wd))
-		return giterr_user_cancel();
+	error = checkout_notify(data, notify, NULL, wd);
 
-	if (remove) {
+	if (!error && remove) {
 		char *path = git_pool_strdup(&data->pool, wd->path);
 		GITERR_CHECK_ALLOC(path);
 
-		if (git_vector_insert(&data->removes, path) < 0)
-			return -1;
+		error = git_vector_insert(&data->removes, path);
 	}
 
-	return 0;
+	return error;
 }
 
 static bool submodule_is_config_only(
@@ -331,35 +327,35 @@ static bool submodule_is_config_only(
 }
 
 static int checkout_action_with_wd(
+	int *action,
 	checkout_data *data,
 	const git_diff_delta *delta,
 	const git_index_entry *wd)
 {
-	int action = CHECKOUT_ACTION__NONE;
+	*action = CHECKOUT_ACTION__NONE;
 
 	switch (delta->status) {
 	case GIT_DELTA_UNMODIFIED: /* case 14/15 or 33 */
 		if (checkout_is_workdir_modified(data, &delta->old_file, wd)) {
-			if (checkout_notify(
-					data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, wd))
-				return giterr_user_cancel();
-			action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, NONE);
+			GITERR_CHECK_ERROR(
+				checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, wd) );
+			*action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, NONE);
 		}
 		break;
 	case GIT_DELTA_ADDED: /* case 3, 4 or 6 */
-		action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, CONFLICT);
+		*action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, CONFLICT);
 		break;
 	case GIT_DELTA_DELETED: /* case 9 or 10 (or 26 but not really) */
 		if (checkout_is_workdir_modified(data, &delta->old_file, wd))
-			action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
+			*action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
 		else
-			action = CHECKOUT_ACTION_IF(SAFE, REMOVE, NONE);
+			*action = CHECKOUT_ACTION_IF(SAFE, REMOVE, NONE);
 		break;
 	case GIT_DELTA_MODIFIED: /* case 16, 17, 18 (or 36 but not really) */
 		if (checkout_is_workdir_modified(data, &delta->old_file, wd))
-			action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, CONFLICT);
+			*action = CHECKOUT_ACTION_IF(FORCE, UPDATE_BLOB, CONFLICT);
 		else
-			action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+			*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
 		break;
 	case GIT_DELTA_TYPECHANGE: /* case 22, 23, 29, 30 */
 		if (delta->old_file.mode == GIT_FILEMODE_TREE) {
@@ -367,92 +363,93 @@ static int checkout_action_with_wd(
 				/* either deleting items in old tree will delete the wd dir,
 				 * or we'll get a conflict when we attempt blob update...
 				 */
-				action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+				*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
 			else if (wd->mode == GIT_FILEMODE_COMMIT) {
 				/* workdir is possibly a "phantom" submodule - treat as a
 				 * tree if the only submodule info came from the config
 				 */
 				if (submodule_is_config_only(data, wd->path))
-					action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+					*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
 				else
-					action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+					*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 			} else
-				action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
+				*action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
 		}
 		else if (checkout_is_workdir_modified(data, &delta->old_file, wd))
-			action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+			*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 		else
-			action = CHECKOUT_ACTION_IF(SAFE, REMOVE_AND_UPDATE, NONE);
+			*action = CHECKOUT_ACTION_IF(SAFE, REMOVE_AND_UPDATE, NONE);
 
 		/* don't update if the typechange is to a tree */
 		if (delta->new_file.mode == GIT_FILEMODE_TREE)
-			action = (action & ~CHECKOUT_ACTION__UPDATE_BLOB);
+			*action = (*action & ~CHECKOUT_ACTION__UPDATE_BLOB);
 		break;
 	default: /* impossible */
 		break;
 	}
 
-	return checkout_action_common(data, action, delta, wd);
+	return checkout_action_common(action, data, delta, wd);
 }
 
 static int checkout_action_with_wd_blocker(
+	int *action,
 	checkout_data *data,
 	const git_diff_delta *delta,
 	const git_index_entry *wd)
 {
-	int action = CHECKOUT_ACTION__NONE;
+	*action = CHECKOUT_ACTION__NONE;
 
 	switch (delta->status) {
 	case GIT_DELTA_UNMODIFIED:
 		/* should show delta as dirty / deleted */
-		if (checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, wd))
-			return giterr_user_cancel();
-		action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, NONE);
+		GITERR_CHECK_ERROR(
+			checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, wd) );
+		*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, NONE);
 		break;
 	case GIT_DELTA_ADDED:
 	case GIT_DELTA_MODIFIED:
-		action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+		*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 		break;
 	case GIT_DELTA_DELETED:
-		action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
+		*action = CHECKOUT_ACTION_IF(FORCE, REMOVE, CONFLICT);
 		break;
 	case GIT_DELTA_TYPECHANGE:
 		/* not 100% certain about this... */
-		action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+		*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 		break;
 	default: /* impossible */
 		break;
 	}
 
-	return checkout_action_common(data, action, delta, wd);
+	return checkout_action_common(action, data, delta, wd);
 }
 
 static int checkout_action_with_wd_dir(
+	int *action,
 	checkout_data *data,
 	const git_diff_delta *delta,
 	const git_index_entry *wd)
 {
-	int action = CHECKOUT_ACTION__NONE;
+	*action = CHECKOUT_ACTION__NONE;
 
 	switch (delta->status) {
 	case GIT_DELTA_UNMODIFIED: /* case 19 or 24 (or 34 but not really) */
-		if (checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, NULL) ||
-			checkout_notify(
-				data, GIT_CHECKOUT_NOTIFY_UNTRACKED, NULL, wd))
-			return giterr_user_cancel();
+		GITERR_CHECK_ERROR(
+			checkout_notify(data, GIT_CHECKOUT_NOTIFY_DIRTY, delta, NULL));
+		GITERR_CHECK_ERROR(
+			checkout_notify(data, GIT_CHECKOUT_NOTIFY_UNTRACKED, NULL, wd));
 		break;
 	case GIT_DELTA_ADDED:/* case 4 (and 7 for dir) */
 	case GIT_DELTA_MODIFIED: /* case 20 (or 37 but not really) */
 		if (delta->old_file.mode == GIT_FILEMODE_COMMIT)
 			/* expected submodule (and maybe found one) */;
 		else if (delta->new_file.mode != GIT_FILEMODE_TREE)
-			action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+			*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 		break;
 	case GIT_DELTA_DELETED: /* case 11 (and 27 for dir) */
-		if (delta->old_file.mode != GIT_FILEMODE_TREE &&
-			checkout_notify(
-				data, GIT_CHECKOUT_NOTIFY_UNTRACKED, NULL, wd))
-			return giterr_user_cancel();
+		if (delta->old_file.mode != GIT_FILEMODE_TREE)
+			GITERR_CHECK_ERROR(
+				checkout_notify(data, GIT_CHECKOUT_NOTIFY_UNTRACKED, NULL, wd));
 		break;
 	case GIT_DELTA_TYPECHANGE: /* case 24 or 31 */
 		if (delta->old_file.mode == GIT_FILEMODE_TREE) {
@@ -462,39 +459,41 @@ static int checkout_action_with_wd_dir(
 			 * directory if is it left empty, so we can defer removing the
 			 * dir and it will succeed if no children are left.
 			 */
-			action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
-			if (action != CHECKOUT_ACTION__NONE)
-				action |= CHECKOUT_ACTION__DEFER_REMOVE;
+			*action = CHECKOUT_ACTION_IF(SAFE, UPDATE_BLOB, NONE);
+			if (*action != CHECKOUT_ACTION__NONE)
+				*action |= CHECKOUT_ACTION__DEFER_REMOVE;
 		}
 		else if (delta->new_file.mode != GIT_FILEMODE_TREE)
 			/* For typechange to dir, dir is already created so no action */
-			action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
+			*action = CHECKOUT_ACTION_IF(FORCE, REMOVE_AND_UPDATE, CONFLICT);
 		break;
 	default: /* impossible */
 		break;
 	}
 
-	return checkout_action_common(data, action, delta, wd);
+	return checkout_action_common(action, data, delta, wd);
 }
 
 static int checkout_action(
+	int *action,
 	checkout_data *data,
 	git_diff_delta *delta,
 	git_iterator *workdir,
-	const git_index_entry **wditem_ptr,
+	const git_index_entry **wditem,
 	git_vector *pathspec)
 {
-	const git_index_entry *wd = *wditem_ptr;
-	int cmp = -1, act;
+	int cmp = -1, error;
 	int (*strcomp)(const char *, const char *) = data->diff->strcomp;
 	int (*pfxcomp)(const char *str, const char *pfx) = data->diff->pfxcomp;
-	int error;
+	int (*advance)(const git_index_entry **, git_iterator *) = NULL;
 
 	/* move workdir iterator to follow along with deltas */
 
 	while (1) {
+		const git_index_entry *wd = *wditem;
+
 		if (!wd)
-			return checkout_action_no_wd(data, delta);
+			return checkout_action_no_wd(action, data, delta);
 
 		cmp = strcomp(wd->path, delta->old_file.path);
 
@@ -512,79 +511,77 @@ static int checkout_action(
 			if (cmp == 0) {
 				if (wd->mode == GIT_FILEMODE_TREE) {
 					/* case 2 - entry prefixed by workdir tree */
-					error = git_iterator_advance_into_or_over(&wd, workdir);
-					if (error && error != GIT_ITEROVER)
-						goto fail;
-					*wditem_ptr = wd;
+					error = git_iterator_advance_into_or_over(wditem, workdir);
+					if (error < 0 && error != GIT_ITEROVER)
+						goto done;
 					continue;
 				}
 
 				/* case 3 maybe - wd contains non-dir where dir expected */
 				if (delta->old_file.path[strlen(wd->path)] == '/') {
-					act = checkout_action_with_wd_blocker(data, delta, wd);
-					*wditem_ptr =
-						git_iterator_advance(&wd, workdir) ? NULL : wd;
-					return act;
+					error = checkout_action_with_wd_blocker(
+						action, data, delta, wd);
+					advance = git_iterator_advance;
+					goto done;
 				}
 			}
 
 			/* case 1 - handle wd item (if it matches pathspec) */
-			if (checkout_action_wd_only(data, workdir, wd, pathspec) < 0)
-				goto fail;
-			if ((error = git_iterator_advance(&wd, workdir)) < 0 &&
+			error = checkout_action_wd_only(data, workdir, wd, pathspec);
+			if (error)
+				goto done;
+			if ((error = git_iterator_advance(wditem, workdir)) < 0 &&
 				error != GIT_ITEROVER)
-				goto fail;
-
-			*wditem_ptr = wd;
+				goto done;
 			continue;
 		}
 
 		if (cmp == 0) {
 			/* case 4 */
-			act = checkout_action_with_wd(data, delta, wd);
-			*wditem_ptr = git_iterator_advance(&wd, workdir) ? NULL : wd;
-			return act;
+			error = checkout_action_with_wd(action, data, delta, wd);
+			advance = git_iterator_advance;
+			goto done;
 		}
 
 		cmp = pfxcomp(wd->path, delta->old_file.path);
 
 		if (cmp == 0) { /* case 5 */
 			if (wd->path[strlen(delta->old_file.path)] != '/')
-				return checkout_action_no_wd(data, delta);
+				return checkout_action_no_wd(action, data, delta);
 
 			if (delta->status == GIT_DELTA_TYPECHANGE) {
 				if (delta->old_file.mode == GIT_FILEMODE_TREE) {
-					act = checkout_action_with_wd(data, delta, wd);
-					if ((error = git_iterator_advance_into(&wd, workdir)) < 0 &&
-						error != GIT_ENOTFOUND)
-						goto fail;
-					*wditem_ptr = wd;
-					return act;
+					error = checkout_action_with_wd(action, data, delta, wd);
+					advance = git_iterator_advance_into;
+					goto done;
 				}
 
 				if (delta->new_file.mode == GIT_FILEMODE_TREE ||
 					delta->new_file.mode == GIT_FILEMODE_COMMIT ||
 					delta->old_file.mode == GIT_FILEMODE_COMMIT)
 				{
-					act = checkout_action_with_wd(data, delta, wd);
-					if ((error = git_iterator_advance(&wd, workdir)) < 0 &&
-						error != GIT_ITEROVER)
-						goto fail;
-					*wditem_ptr = wd;
-					return act;
+					error = checkout_action_with_wd(action, data, delta, wd);
+					advance = git_iterator_advance;
+					goto done;
 				}
 			}
 
-			return checkout_action_with_wd_dir(data, delta, wd);
+			return checkout_action_with_wd_dir(action, data, delta, wd);
 		}
 
 		/* case 6 - wd is after delta */
-		return checkout_action_no_wd(data, delta);
+		return checkout_action_no_wd(action, data, delta);
 	}
 
-fail:
-	*wditem_ptr = NULL;
-	return -1;
+done:
+	if (!error && advance != NULL &&
+		(error = advance(wditem, workdir)) < 0) {
+		*wditem = NULL;
+		if (error == GIT_ITEROVER)
+			error = 0;
+	}
+
+	return error;
 }
 
 static int checkout_remaining_wd_items(
@@ -965,7 +962,7 @@ static int checkout_get_actions(
 	checkout_data *data,
 	git_iterator *workdir)
 {
-	int error = 0;
+	int error = 0, act;
 	const git_index_entry *wditem;
 	git_vector pathspec = GIT_VECTOR_INIT, *deltas;
 	git_pool pathpool = GIT_POOL_INIT_STRINGPOOL;
@@ -992,12 +989,9 @@ static int checkout_get_actions(
 	}
 
 	git_vector_foreach(deltas, i, delta) {
-		int act = checkout_action(data, delta, workdir, &wditem, &pathspec);
-
-		if (act < 0) {
-			error = act;
+		error = checkout_action(&act, data, delta, workdir, &wditem, &pathspec);
+		if (error)
 			goto fail;
-		}
 
 		actions[i] = act;
 
@@ -1012,7 +1006,7 @@ static int checkout_get_actions(
 	}
 
 	error = checkout_remaining_wd_items(data, workdir, wditem, &pathspec);
-	if (error < 0)
+	if (error)
 		goto fail;
 
 	counts[CHECKOUT_ACTION__REMOVE] += data->removes.length;
diff --git a/src/clone.c b/src/clone.c
index 415efabba..ffbe8f8af 100644
--- a/src/clone.c
+++ b/src/clone.c
@@ -107,7 +107,6 @@ struct head_info {
 	git_buf branchname;
 	const git_refspec *refspec;
 	bool found;
-	git_error_state error;
 };
 
 static int reference_matches_remote_head(
@@ -147,7 +146,7 @@ static int reference_matches_remote_head(
 		}
 	}
 
-	return giterr_capture(&head_info->error, error);
+	return error;
 }
 
 static int update_head_to_new_branch(
@@ -209,12 +208,8 @@ static int update_head_to_remote(git_repository *repo, git_remote *remote)
 	/* Check to see if the remote HEAD points to the remote master */
 	error = reference_matches_remote_head(
 		git_buf_cstr(&remote_master_name), &head_info);
-
-	if (error < 0) {
-		error = giterr_restore(&head_info.error);
-		if (error < 0 && error != GIT_ITEROVER)
-			goto cleanup;
-	}
+	if (error < 0 && error != GIT_ITEROVER)
+		goto cleanup;
 
 	if (head_info.found) {
 		error = update_head_to_new_branch(
@@ -227,9 +222,6 @@ static int update_head_to_remote(git_repository *repo, git_remote *remote)
 	/* Not master. Check all the other refs. */
 	error = git_reference_foreach_name(
 		repo, reference_matches_remote_head, &head_info);
-
-	if (error == GIT_EUSER)
-		error = giterr_restore(&head_info.error);
 	if (error < 0 && error != GIT_ITEROVER)
 		goto cleanup;
 
@@ -349,7 +341,7 @@ int git_clone_into(git_repository *repo, git_remote *remote, const git_checkout_
 	old_fetchhead = git_remote_update_fetchhead(remote);
 	git_remote_set_update_fetchhead(remote, 0);
 
-	if ((error = git_remote_fetch(remote)) < 0)
+	if ((error = git_remote_fetch(remote)) != 0)
 		goto cleanup;
 
 	if (branch)
@@ -363,10 +355,12 @@ int git_clone_into(git_repository *repo, git_remote *remote, const git_checkout_
 
 cleanup:
 	git_remote_set_update_fetchhead(remote, old_fetchhead);
+
 	/* Go back to the original refspecs */
-	if (git_remote_set_fetch_refspecs(remote, &refspecs) < 0) {
-		git_strarray_free(&refspecs);
-		return -1;
+	{
+		int error_alt = git_remote_set_fetch_refspecs(remote, &refspecs);
+		if (!error)
+			error = error_alt;
 	}
 
 	git_strarray_free(&refspecs);
diff --git a/src/common.h b/src/common.h
index 0ad4130aa..a0e47df9a 100644
--- a/src/common.h
+++ b/src/common.h
@@ -62,7 +62,7 @@
  * Check a return value and propogate result if non-zero.
  */
 #define GITERR_CHECK_ERROR(code) \
-	do { int _err = (code); if (_err < 0) return _err; } while (0)
+	do { int _err = (code); if (_err) return _err; } while (0)
 
 /**
  * Set the error message for this thread, formatting as needed.
@@ -76,6 +76,27 @@ void giterr_set(int error_class, const char *string, ...);
 int giterr_set_regex(const regex_t *regex, int error_code);
 
 /**
+ * Set error message for user callback if needed.
+ *
+ * If the error code in non-zero and no error message is set, this
+ * sets a generic error message.
+ *
+ * @return This always returns the `error_code` parameter.
+ */
+GIT_INLINE(int) giterr_set_callback(int error_code, const char *action)
+{
+	if (error_code) {
+		const git_error *e = giterr_last();
+		if (!e || !e->message)
+			giterr_set(e ? e->klass : GITERR_CALLBACK,
+				"%s callback returned %d", action, error_code);
+	}
+	return error_code;
+}
+
+#define GITERR_CALLBACK(code) giterr_set_callback((code), __func__)
+
+/**
  * Gets the system error code for this thread.
  */
 int giterr_system_last(void);
@@ -86,15 +107,6 @@ int giterr_system_last(void);
 void giterr_system_set(int code);
 
 /**
- * Note that a user cancelled an operation with GIT_EUSER
- */
-GIT_INLINE(int) giterr_user_cancel(void)
-{
-	giterr_clear();
-	return GIT_EUSER;
-}
-
-/**
  * Structure to preserve libgit2 error state
  */
 typedef struct {
diff --git a/src/config.c b/src/config.c
index 3af9d58de..8b3a426ed 100644
--- a/src/config.c
+++ b/src/config.c
@@ -480,23 +480,23 @@ int git_config_foreach(
 int git_config_backend_foreach_match(
 	git_config_backend *backend,
 	const char *regexp,
-	int (*fn)(const git_config_entry *, void *),
-	void *data)
+	git_config_foreach_cb cb,
+	void *payload)
 {
 	git_config_entry *entry;
 	git_config_iterator* iter;
 	regex_t regex;
-	int result = 0;
+	int error = 0;
 
 	if (regexp != NULL) {
-		if ((result = regcomp(&regex, regexp, REG_EXTENDED)) < 0) {
-			giterr_set_regex(&regex, result);
+		if ((error = regcomp(&regex, regexp, REG_EXTENDED)) < 0) {
+			giterr_set_regex(&regex, error);
 			regfree(&regex);
 			return -1;
 		}
 	}
 
-	if ((result = backend->iterator(&iter, backend)) < 0) {
+	if ((error = backend->iterator(&iter, backend)) < 0) {
 		iter = NULL;
 		return -1;
 	}
@@ -507,10 +507,9 @@ int git_config_backend_foreach_match(
 			continue;
 
 		/* abort iterator on non-zero return value */
-		if (fn(entry, data)) {
-			result = giterr_user_cancel();
+		error = GITERR_CALLBACK( cb(entry, payload) );
+		if (error)
 			break;
-		}
 	}
 
 	if (regexp != NULL)
@@ -518,7 +517,7 @@ int git_config_backend_foreach_match(
 
 	iter->free(iter);
 
-	return result;
+	return error;
 }
 
 int git_config_foreach_match(
@@ -534,12 +533,9 @@ int git_config_foreach_match(
 	if ((error = git_config_iterator_glob_new(&iter, cfg, regexp)) < 0)
 		return error;
 
-	while ((error = git_config_next(&entry, iter)) == 0) {
-		if (cb(entry, payload)) {
-			error = giterr_user_cancel();
-			break;
-		}
-	}
+	while (!(error = git_config_next(&entry, iter)) &&
+		   !(error = GITERR_CALLBACK( cb(entry, payload) )))
+		/* make callback on each config */;
 
 	git_config_iterator_free(iter);
 
@@ -798,10 +794,8 @@ int git_config_get_multivar_foreach(
 	while ((err = iter->next(&entry, iter)) == 0) {
 		found = 1;
 
-		if (cb(entry, payload)) {
-			iter->free(iter);
-			return giterr_user_cancel();
-		}
+		if ((err = GITERR_CALLBACK( cb(entry, payload) )) != 0)
+			break;
 	}
 
 	iter->free(iter);
@@ -1212,7 +1206,6 @@ struct rename_data {
 	git_config *config;
 	git_buf *name;
 	size_t old_len;
-	git_error_state error;
 };
 
 static int rename_config_entries_cb(
@@ -1235,8 +1228,7 @@ static int rename_config_entries_cb(
 	if (!error)
 		error = git_config_delete_entry(data->config, entry->name);
 
-	/* capture error message as needed, since it will become EUSER */
-	return giterr_capture(&data->error, error);
+	return error;
 }
 
 int git_config_rename_section(
@@ -1257,7 +1249,6 @@ int git_config_rename_section(
 	if ((error = git_repository_config__weakptr(&config, repo)) < 0)
 		goto cleanup;
 
-	memset(&data, 0, sizeof(data));
 	data.config  = config;
 	data.name    = &replace;
 	data.old_len = strlen(old_section_name) + 1;
@@ -1277,9 +1268,6 @@ int git_config_rename_section(
 	error = git_config_foreach_match(
 		config, git_buf_cstr(&pattern), rename_config_entries_cb, &data);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
-
 cleanup:
 	git_buf_free(&pattern);
 	git_buf_free(&replace);
diff --git a/src/diff.c b/src/diff.c
index af47e86aa..101426f6e 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -49,16 +49,25 @@ static git_diff_delta *diff_delta__alloc(
 	return delta;
 }
 
-static int diff_notify(
-	const git_diff *diff,
-	const git_diff_delta *delta,
-	const char *matched_pathspec)
+static int diff_insert_delta(
+	git_diff *diff, git_diff_delta *delta, const char *matched_pathspec)
 {
-	if (!diff->opts.notify_cb)
-		return 0;
+	int error = 0;
+
+	if (diff->opts.notify_cb) {
+		error = diff->opts.notify_cb(
+			diff, delta, matched_pathspec, diff->opts.notify_payload);
+
+		if (error) {
+			git__free(delta);
+			return (error > 0) ? 0 : giterr_set_callback(error, "git_diff");
+		}
+	}
+
+	if ((error = git_vector_insert(&diff->deltas, delta)) < 0)
+		git__free(delta);
 
-	return diff->opts.notify_cb(
-		diff, delta, matched_pathspec, diff->opts.notify_payload);
+	return error;
 }
 
 static int diff_delta__from_one(
@@ -68,7 +77,6 @@ static int diff_delta__from_one(
 {
 	git_diff_delta *delta;
 	const char *matched_pathspec;
-	int notify_res;
 
 	if ((entry->flags & GIT_IDXENTRY_VALID) != 0)
 		return 0;
@@ -111,21 +119,12 @@ static int diff_delta__from_one(
 		!git_oid_iszero(&delta->new_file.oid))
 		delta->new_file.flags |= GIT_DIFF_FLAG_VALID_OID;
 
-	notify_res = diff_notify(diff, delta, matched_pathspec);
-
-	if (notify_res)
-		git__free(delta);
-	else if (git_vector_insert(&diff->deltas, delta) < 0) {
-		git__free(delta);
-		return -1;
-	}
-
-	return notify_res < 0 ? giterr_user_cancel() : 0;
+	return diff_insert_delta(diff, delta, matched_pathspec);
 }
 
 static int diff_delta__from_two(
 	git_diff *diff,
-	git_delta_t   status,
+	git_delta_t status,
 	const git_index_entry *old_entry,
 	uint32_t old_mode,
 	const git_index_entry *new_entry,
@@ -134,7 +133,6 @@ static int diff_delta__from_two(
 	const char *matched_pathspec)
 {
 	git_diff_delta *delta;
-	int notify_res;
 	const char *canonical_path = old_entry->path;
 
 	if (status == GIT_DELTA_UNMODIFIED &&
@@ -173,16 +171,7 @@ static int diff_delta__from_two(
 	if (new_oid || !git_oid_iszero(&new_entry->oid))
 		delta->new_file.flags |= GIT_DIFF_FLAG_VALID_OID;
 
-	notify_res = diff_notify(diff, delta, matched_pathspec);
-
-	if (notify_res)
-		git__free(delta);
-	else if (git_vector_insert(&diff->deltas, delta) < 0) {
-		git__free(delta);
-		return -1;
-	}
-
-	return notify_res < 0 ? giterr_user_cancel() : 0;
+	return diff_insert_delta(diff, delta, matched_pathspec);
 }
 
 static git_diff_delta *diff_delta__last_for_item(
@@ -654,6 +643,7 @@ static int maybe_modified(
 	unsigned int nmode = nitem->mode;
 	bool new_is_workdir = (info->new_iter->type == GIT_ITERATOR_TYPE_WORKDIR);
 	const char *matched_pathspec;
+	int error = 0;
 
 	if (!git_pathspec__match(
 			&diff->pathspec, oitem->path,
@@ -688,10 +678,9 @@ static int maybe_modified(
 		if (DIFF_FLAG_IS_SET(diff, GIT_DIFF_INCLUDE_TYPECHANGE))
 			status = GIT_DELTA_TYPECHANGE;
 		else {
-			if (diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem) < 0 ||
-				diff_delta__from_one(diff, GIT_DELTA_ADDED, nitem) < 0)
-				return -1;
-			return 0;
+			if (!(error = diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem)))
+				error = diff_delta__from_one(diff, GIT_DELTA_ADDED, nitem);
+			return error;
 		}
 	}
 
@@ -713,8 +702,8 @@ static int maybe_modified(
 		/* TODO: add check against index file st_mtime to avoid racy-git */
 
 		if (S_ISGITLINK(nmode)) {
-			if (maybe_modified_submodule(&status, &noid, diff, info) < 0)
-				return -1;
+			if ((error = maybe_modified_submodule(&status, &noid, diff, info)) < 0)
+				return error;
 		}
 
 		/* if the stat data looks different, then mark modified - this just
@@ -741,9 +730,9 @@ static int maybe_modified(
 	 */
 	if (status == GIT_DELTA_MODIFIED && git_oid_iszero(&nitem->oid)) {
 		if (git_oid_iszero(&noid)) {
-			if (git_diff__oid_for_file(diff->repo,
-					nitem->path, nitem->mode, nitem->file_size, &noid) < 0)
-				return -1;
+			if ((error = git_diff__oid_for_file(diff->repo,
+					nitem->path, nitem->mode, nitem->file_size, &noid)) < 0)
+				return error;
 		}
 
 		/* if oid matches, then mark unmodified (except submodules, where
@@ -898,7 +887,7 @@ static int handle_unmatched_new_item(
 			git_diff_delta *last;
 
 			/* attempt to insert record for this directory */
-			if ((error = diff_delta__from_one(diff, delta_type, nitem)) < 0)
+			if ((error = diff_delta__from_one(diff, delta_type, nitem)) != 0)
 				return error;
 
 			/* if delta wasn't created (because of rules), just skip ahead */
@@ -977,7 +966,7 @@ static int handle_unmatched_new_item(
 	}
 
 	/* Actually create the record for this item if necessary */
-	if ((error = diff_delta__from_one(diff, delta_type, nitem)) < 0)
+	if ((error = diff_delta__from_one(diff, delta_type, nitem)) != 0)
 		return error;
 
 	/* If user requested TYPECHANGE records, then check for that instead of
@@ -1002,7 +991,7 @@ static int handle_unmatched_old_item(
 	git_diff *diff, diff_in_progress *info)
 {
 	int error = diff_delta__from_one(diff, GIT_DELTA_DELETED, info->oitem);
-	if (error < 0)
+	if (error != 0)
 		return error;
 
 	/* if we are generating TYPECHANGE records then check for that
@@ -1399,10 +1388,8 @@ int git_diff__paired_foreach(
 			i++; j++;
 		}
 
-		if (cb(h2i, i2w, payload)) {
-			error = giterr_user_cancel();
+		if ((error = GITERR_CALLBACK( cb(h2i, i2w, payload) )) != 0)
 			break;
-		}
 	}
 
 	/* restore case-insensitive delta sort */
diff --git a/src/diff_patch.c b/src/diff_patch.c
index c0910558e..11f02478d 100644
--- a/src/diff_patch.c
+++ b/src/diff_patch.c
@@ -32,7 +32,6 @@ struct git_patch {
 	git_array_t(git_diff_line)   lines;
 	size_t content_size, context_size, header_size;
 	git_pool flattened;
-	git_error_state error;
 };
 
 enum {
@@ -200,11 +199,12 @@ static int diff_patch_invoke_file_callback(
 	float progress = patch->diff ?
 		((float)patch->delta_index / patch->diff->deltas.length) : 1.0f;
 
-	if (output->file_cb &&
-		output->file_cb(patch->delta, progress, output->payload) != 0)
-		return giterr_user_cancel();
+	if (!output->file_cb)
+		return 0;
 
-	return 0;
+	return giterr_set_callback(
+		output->file_cb(patch->delta, progress, output->payload),
+		"git_patch");
 }
 
 static int diff_patch_generate(git_patch *patch, git_diff_output *output)
@@ -291,7 +291,7 @@ int git_diff_foreach(
 
 		git_patch_free(&patch);
 
-		if (error < 0)
+		if (error)
 			break;
 	}
 
@@ -331,9 +331,6 @@ static int diff_single_generate(diff_patch_with_delta *pd, git_xdiff_output *xo)
 	if (!error)
 		error = diff_patch_generate(patch, (git_diff_output *)xo);
 
-	if (error == GIT_EUSER)
-		giterr_clear(); /* don't leave error message set invalidly */
-
 	return error;
 }
 
@@ -462,9 +459,6 @@ int git_patch_from_blobs(
 	error = diff_patch_from_blobs(
 		pd, &xo, old_blob, old_path, new_blob, new_path, opts);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&pd->patch.error);
-
 	if (!error)
 		*out = (git_patch *)pd;
 	else
@@ -576,9 +570,6 @@ int git_patch_from_blob_and_buffer(
 	error = diff_patch_from_blob_and_buffer(
 		pd, &xo, old_blob, old_path, buf, buflen, buf_path, opts);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&pd->patch.error);
-
 	if (!error)
 		*out = (git_patch *)pd;
 	else
@@ -627,12 +618,9 @@ int git_patch_from_diff(
 	if (!error)
 		error = diff_patch_generate(patch, &xo.output);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&patch->error);
-
 	if (!error) {
-		/* if cumulative diff size is < 0.5 total size, flatten the patch */
-		/* unload the file content */
+		/* TODO: if cumulative diff size is < 0.5 total size, flatten patch */
+		/* TODO: and unload the file content */
 	}
 
 	if (error || !patch_ptr)
@@ -640,8 +628,6 @@ int git_patch_from_diff(
 	else
 		*patch_ptr = patch;
 
-	if (error == GIT_EUSER)
-		giterr_clear(); /* don't leave error message set invalidly */
 	return error;
 }
 
@@ -879,8 +865,7 @@ static int diff_patch_hunk_cb(
 	GIT_UNUSED(delta);
 
 	hunk = git_array_alloc(patch->hunks);
-	if (!hunk)
-		return giterr_capture(&patch->error, -1);
+	GITERR_CHECK_ALLOC(hunk);
 
 	memcpy(&hunk->hunk, hunk_, sizeof(hunk->hunk));
 
@@ -909,8 +894,7 @@ static int diff_patch_line_cb(
 	assert(hunk); /* programmer error if no hunk is available */
 
 	line = git_array_alloc(patch->lines);
-	if (!line)
-		return giterr_capture(&patch->error, -1);
+	GITERR_CHECK_ALLOC(line);
 
 	memcpy(line, line_, sizeof(*line));
 
diff --git a/src/diff_print.c b/src/diff_print.c
index 712402864..ff477e4c8 100644
--- a/src/diff_print.c
+++ b/src/diff_print.c
@@ -18,7 +18,6 @@ typedef struct {
 	uint32_t flags;
 	int oid_strlen;
 	git_diff_line line;
-	git_error_state error;
 } diff_print_info;
 
 static int diff_print_info_init(
@@ -34,7 +33,6 @@ static int diff_print_info_init(
 	pi->print_cb = cb;
 	pi->payload  = payload;
 	pi->buf      = out;
-	memset(&pi->error, 0, sizeof(pi->error));
 
 	if (diff)
 		pi->flags = diff->opts.flags;
@@ -104,19 +102,16 @@ static int diff_print_one_name_only(
 		return 0;
 
 	git_buf_clear(out);
-
-	if (git_buf_puts(out, delta->new_file.path) < 0 ||
-		git_buf_putc(out, '\n'))
-		return giterr_capture(&pi->error, -1);
+	git_buf_puts(out, delta->new_file.path);
+	git_buf_putc(out, '\n');
+	if (git_buf_oom(out))
+		return -1;
 
 	pi->line.origin      = GIT_DIFF_LINE_FILE_HDR;
 	pi->line.content     = git_buf_cstr(out);
 	pi->line.content_len = git_buf_len(out);
 
-	if (pi->print_cb(delta, NULL, &pi->line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(delta, NULL, &pi->line, pi->payload);
 }
 
 static int diff_print_one_name_status(
@@ -150,18 +145,14 @@ static int diff_print_one_name_status(
 		git_buf_printf(out, "%c\t%s%c\n", code, delta->old_file.path, old_suffix);
 	else
 		git_buf_printf(out, "%c\t%s\n", code, delta->old_file.path);
-
 	if (git_buf_oom(out))
-		return giterr_capture(&pi->error, -1);
+		return -1;
 
 	pi->line.origin      = GIT_DIFF_LINE_FILE_HDR;
 	pi->line.content     = git_buf_cstr(out);
 	pi->line.content_len = git_buf_len(out);
 
-	if (pi->print_cb(delta, NULL, &pi->line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(delta, NULL, &pi->line, pi->payload);
 }
 
 static int diff_print_one_raw(
@@ -198,16 +189,13 @@ static int diff_print_one_raw(
 			delta->old_file.path : delta->new_file.path);
 
 	if (git_buf_oom(out))
-		return giterr_capture(&pi->error, -1);
+		return -1;
 
 	pi->line.origin      = GIT_DIFF_LINE_FILE_HDR;
 	pi->line.content     = git_buf_cstr(out);
 	pi->line.content_len = git_buf_len(out);
 
-	if (pi->print_cb(delta, NULL, &pi->line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(delta, NULL, &pi->line, pi->payload);
 }
 
 static int diff_print_oid_range(
@@ -234,10 +222,7 @@ static int diff_print_oid_range(
 		git_buf_printf(out, "index %s..%s\n", start_oid, end_oid);
 	}
 
-	if (git_buf_oom(out))
-		return -1;
-
-	return 0;
+	return git_buf_oom(out) ? -1 : 0;
 }
 
 static int diff_delta_format_with_paths(
@@ -281,8 +266,7 @@ int git_diff_delta__format_file_header(
 	git_buf_printf(out, "diff --git %s%s %s%s\n",
 		oldpfx, delta->old_file.path, newpfx, delta->new_file.path);
 
-	if (diff_print_oid_range(out, delta, oid_strlen) < 0)
-		return -1;
+	GITERR_CHECK_ERROR(diff_print_oid_range(out, delta, oid_strlen));
 
 	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0)
 		diff_delta_format_with_paths(
@@ -294,6 +278,7 @@ int git_diff_delta__format_file_header(
 static int diff_print_patch_file(
 	const git_diff_delta *delta, float progress, void *data)
 {
+	int error;
 	diff_print_info *pi = data;
 	const char *oldpfx =
 		pi->diff ? pi->diff->opts.old_prefix : DIFF_OLD_PREFIX_DEFAULT;
@@ -309,36 +294,33 @@ static int diff_print_patch_file(
 		 (pi->flags & GIT_DIFF_SHOW_UNTRACKED_CONTENT) == 0))
 		return 0;
 
-	if (git_diff_delta__format_file_header(
-			pi->buf, delta, oldpfx, newpfx, pi->oid_strlen) < 0)
-		return giterr_capture(&pi->error, -1);
+	if ((error = git_diff_delta__format_file_header(
+			pi->buf, delta, oldpfx, newpfx, pi->oid_strlen)) < 0)
+		return error;
 
 	pi->line.origin      = GIT_DIFF_LINE_FILE_HDR;
 	pi->line.content     = git_buf_cstr(pi->buf);
 	pi->line.content_len = git_buf_len(pi->buf);
 
-	if (pi->print_cb(delta, NULL, &pi->line, pi->payload))
-		return giterr_user_cancel();
+	if ((error = pi->print_cb(delta, NULL, &pi->line, pi->payload)) != 0)
+		return error;
 
 	if ((delta->flags & GIT_DIFF_FLAG_BINARY) == 0)
 		return 0;
 
 	git_buf_clear(pi->buf);
 
-	if (diff_delta_format_with_paths(
+	if ((error = diff_delta_format_with_paths(
 			pi->buf, delta, oldpfx, newpfx,
-			"Binary files %s%s and %s%s differ\n") < 0)
-		return giterr_capture(&pi->error, -1);
+			"Binary files %s%s and %s%s differ\n")) < 0)
+		return error;
 
 	pi->line.origin      = GIT_DIFF_LINE_BINARY;
 	pi->line.content     = git_buf_cstr(pi->buf);
 	pi->line.content_len = git_buf_len(pi->buf);
 	pi->line.num_lines   = 1;
 
-	if (pi->print_cb(delta, NULL, &pi->line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(delta, NULL, &pi->line, pi->payload);
 }
 
 static int diff_print_patch_hunk(
@@ -355,10 +337,7 @@ static int diff_print_patch_hunk(
 	pi->line.content     = h->header;
 	pi->line.content_len = h->header_len;
 
-	if (pi->print_cb(d, h, &pi->line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(d, h, &pi->line, pi->payload);
 }
 
 static int diff_print_patch_line(
@@ -372,10 +351,7 @@ static int diff_print_patch_line(
 	if (S_ISDIR(delta->new_file.mode))
 		return 0;
 
-	if (pi->print_cb(delta, hunk, line, pi->payload))
-		return giterr_user_cancel();
-
-	return 0;
+	return pi->print_cb(delta, hunk, line, pi->payload);
 }
 
 /* print a git_diff to an output callback */
@@ -421,8 +397,8 @@ int git_diff_print(
 		error = git_diff_foreach(
 			diff, print_file, print_hunk, print_line, &pi);
 
-		if (error == GIT_EUSER && pi.error.error_code)
-			error = giterr_restore(&pi.error);
+		if (error) /* make sure error message is set */
+			giterr_set_callback(error, "git_diff_print");
 	}
 
 	git_buf_free(&buf);
@@ -450,8 +426,8 @@ int git_patch_print(
 			patch, diff_print_patch_file, diff_print_patch_hunk,
 			diff_print_patch_line, &pi);
 
-		if (error && error != GIT_EUSER)
-			error = giterr_restore(&pi.error);
+		if (error) /* make sure error message is set */
+			giterr_set_callback(error, "git_patch_print");
 	}
 
 	git_buf_free(&temp);
@@ -484,17 +460,12 @@ int git_patch_to_str(
 	int error;
 	git_buf output = GIT_BUF_INIT;
 
-	error = git_patch_print(patch, diff_print_to_buffer_cb, &output);
-
-	/* GIT_EUSER means git_buf_put in print_to_buffer_cb returned -1,
-	 * meaning a memory allocation failure, so just map to -1...
-	 */
-	if (error == GIT_EUSER) {
-		giterr_set_oom();
-		error = -1;
+	if (!(error = git_patch_print(patch, diff_print_to_buffer_cb, &output)))
+		*string = git_buf_detach(&output);
+	else {
+		git_buf_free(&output);
+		*string = NULL;
 	}
 
-	*string = git_buf_detach(&output);
-
 	return error;
 }
diff --git a/src/diff_xdiff.c b/src/diff_xdiff.c
index c6ca48882..e5984f1c9 100644
--- a/src/diff_xdiff.c
+++ b/src/diff_xdiff.c
@@ -126,8 +126,9 @@ static int git_xdiff_cb(void *priv, mmbuffer_t *bufs, int len)
 		info->hunk.header[info->hunk.header_len] = '\0';
 
 		if (output->hunk_cb != NULL &&
-			output->hunk_cb(delta, &info->hunk, output->payload))
-			return (output->error = giterr_user_cancel());
+			(output->error = output->hunk_cb(
+				delta, &info->hunk, output->payload)))
+			return output->error;
 
 		info->old_lineno = info->hunk.old_start;
 		info->new_lineno = info->hunk.new_start;
@@ -150,10 +151,9 @@ static int git_xdiff_cb(void *priv, mmbuffer_t *bufs, int len)
 		output->error = diff_update_lines(
 			info, &line, bufs[1].ptr, bufs[1].size);
 
-		if (!output->error &&
-			output->data_cb != NULL &&
-			output->data_cb(delta, &info->hunk, &line, output->payload))
-			output->error = giterr_user_cancel();
+		if (!output->error && output->data_cb != NULL)
+			output->error = output->data_cb(
+				delta, &info->hunk, &line, output->payload);
 	}
 
 	if (len == 3 && !output->error) {
@@ -172,10 +172,9 @@ static int git_xdiff_cb(void *priv, mmbuffer_t *bufs, int len)
 		output->error = diff_update_lines(
 			info, &line, bufs[2].ptr, bufs[2].size);
 
-		if (!output->error &&
-			output->data_cb != NULL &&
-			output->data_cb(delta, &info->hunk, &line, output->payload))
-			output->error = giterr_user_cancel();
+		if (!output->error && output->data_cb != NULL)
+			output->error = output->data_cb(
+				delta, &info->hunk, &line, output->payload);
 	}
 
 	return output->error;
diff --git a/src/fetch.c b/src/fetch.c
index 276591821..5bf2b93c1 100644
--- a/src/fetch.c
+++ b/src/fetch.c
@@ -104,7 +104,7 @@ cleanup:
 int git_fetch_negotiate(git_remote *remote)
 {
 	git_transport *t = remote->transport;
-	
+
 	if (filter_wants(remote) < 0) {
 		giterr_set(GITERR_NET, "Failed to filter the reference list for wants");
 		return -1;
@@ -128,9 +128,9 @@ int git_fetch_download_pack(git_remote *remote)
 {
 	git_transport *t = remote->transport;
 
-	if(!remote->need_pack)
+	if (!remote->need_pack)
 		return 0;
 
 	return t->download_pack(t, remote->repo, &remote->stats,
-				remote->callbacks.transfer_progress, remote->callbacks.payload);
+			remote->callbacks.transfer_progress, remote->callbacks.payload);
 }
diff --git a/src/fetchhead.c b/src/fetchhead.c
index ee1492211..7c37be4c6 100644
--- a/src/fetchhead.c
+++ b/src/fetchhead.c
@@ -269,10 +269,10 @@ int git_repository_fetchhead_foreach(git_repository *repo,
 		else
 			ref_name = NULL;
 
-		if (cb(ref_name, remote_url, &oid, is_merge, payload) != 0) {
-			error = giterr_user_cancel();
+		error = GITERR_CALLBACK(
+			cb(ref_name, remote_url, &oid, is_merge, payload) );
+		if (error)
 			goto done;
-		}
 	}
 
 	if (*buffer) {
diff --git a/src/fileops.c b/src/fileops.c
index 0418e9e52..98dcd3269 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -404,7 +404,6 @@ typedef struct {
 	size_t baselen;
 	uint32_t flags;
 	int depth;
-	git_error_state error;
 } futils__rmdir_data;
 
 #define FUTILS_MAX_DEPTH 100
@@ -474,16 +473,14 @@ static int futils__rmdir_recurs_foreach(void *opaque, git_buf *path)
 		data->depth++;
 
 		error = git_path_direach(path, 0, futils__rmdir_recurs_foreach, data);
-		if (error == GIT_EUSER)
-			return error;
 
 		data->depth--;
 
 		if (error < 0)
-			goto done;
+			return error;
 
 		if (data->depth == 0 && (data->flags & GIT_RMDIR_SKIP_ROOT) != 0)
-			goto done;
+			return error;
 
 		if ((error = p_rmdir(path->ptr)) < 0) {
 			if ((data->flags & GIT_RMDIR_SKIP_NONEMPTY) != 0 &&
@@ -502,8 +499,7 @@ static int futils__rmdir_recurs_foreach(void *opaque, git_buf *path)
 	else if ((data->flags & GIT_RMDIR_SKIP_NONEMPTY) == 0)
 		error = futils__error_cannot_rmdir(path->ptr, "still present");
 
-done:
-	return giterr_capture(&data->error, error);
+	return error;
 }
 
 static int futils__rmdir_empty_parent(void *opaque, git_buf *path)
@@ -512,9 +508,9 @@ static int futils__rmdir_empty_parent(void *opaque, git_buf *path)
 	int error = 0;
 
 	if (git_buf_len(path) <= data->baselen)
-		return giterr_capture(&data->error, GIT_ITEROVER);
+		error = GIT_ITEROVER;
 
-	if (p_rmdir(git_buf_cstr(path)) < 0) {
+	else if (p_rmdir(git_buf_cstr(path)) < 0) {
 		int en = errno;
 
 		if (en == ENOENT || en == ENOTDIR) {
@@ -526,7 +522,7 @@ static int futils__rmdir_empty_parent(void *opaque, git_buf *path)
 		}
 	}
 
-	return giterr_capture(&data->error, error);
+	return error;
 }
 
 int git_futils_rmdir_r(
@@ -552,10 +548,10 @@ int git_futils_rmdir_r(
 		error = git_path_walk_up(
 			&fullpath, base, futils__rmdir_empty_parent, &data);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
-	if (error == GIT_ITEROVER)
+	if (error == GIT_ITEROVER) {
+		giterr_clear();
 		error = 0;
+	}
 
 	git_buf_free(&fullpath);
 
@@ -859,7 +855,6 @@ typedef struct {
 	uint32_t flags;
 	uint32_t mkdir_flags;
 	mode_t dirmode;
-	git_error_state error;
 } cp_r_info;
 
 #define GIT_CPDIR__MKDIR_DONE_FOR_TO_ROOT (1u << 10)
@@ -899,19 +894,19 @@ static int _cp_r_callback(void *ref, git_buf *from)
 
 	if ((error = git_buf_joinpath(
 			&info->to, info->to_root, from->ptr + info->from_prefix)) < 0)
-		goto done;
+		return error;
 
 	if (!(error = git_path_lstat(info->to.ptr, &to_st)))
 		exists = true;
 	else if (error != GIT_ENOTFOUND)
-		goto done;
+		return error;
 	else {
 		giterr_clear();
 		error = 0;
 	}
 
 	if ((error = git_path_lstat(from->ptr, &from_st)) < 0)
-		goto done;
+		return error;
 
 	if (S_ISDIR(from_st.st_mode)) {
 		mode_t oldmode = info->dirmode;
@@ -925,16 +920,13 @@ static int _cp_r_callback(void *ref, git_buf *from)
 			error = _cp_r_mkdir(info, from);
 
 		/* recurse onto target directory */
-		if (!error && (!exists || S_ISDIR(to_st.st_mode))) {
+		if (!error && (!exists || S_ISDIR(to_st.st_mode)))
 			error = git_path_direach(from, 0, _cp_r_callback, info);
-			if (error == GIT_EUSER)
-				return error;
-		}
 
 		if (oldmode != 0)
 			info->dirmode = oldmode;
 
-		goto done;
+		return error;
 	}
 
 	if (exists) {
@@ -944,8 +936,7 @@ static int _cp_r_callback(void *ref, git_buf *from)
 		if (p_unlink(info->to.ptr) < 0) {
 			giterr_set(GITERR_OS, "Cannot overwrite existing file '%s'",
 				info->to.ptr);
-			error = -1;
-			goto done;
+			return GIT_EEXISTS;
 		}
 	}
 
@@ -958,7 +949,7 @@ static int _cp_r_callback(void *ref, git_buf *from)
 	/* Make container directory on demand if needed */
 	if ((info->flags & GIT_CPDIR_CREATE_EMPTY_DIRS) == 0 &&
 		(error = _cp_r_mkdir(info, from)) < 0)
-		goto done;
+		return error;
 
 	/* make symlink or regular file */
 	if (S_ISLNK(from_st.st_mode))
@@ -972,8 +963,7 @@ static int _cp_r_callback(void *ref, git_buf *from)
 		error = git_futils_cp(from->ptr, info->to.ptr, usemode);
 	}
 
-done:
-	return giterr_capture(&info->error, error);
+	return error;
 }
 
 int git_futils_cp_r(
@@ -1015,9 +1005,6 @@ int git_futils_cp_r(
 	git_buf_free(&path);
 	git_buf_free(&info.to);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&info.error);
-
 	return error;
 }
 
diff --git a/src/ignore.c b/src/ignore.c
index aa53d409d..c79fe4871 100644
--- a/src/ignore.c
+++ b/src/ignore.c
@@ -74,20 +74,12 @@ static int parse_ignore_file(
 #define push_ignore_file(R,IGN,S,B,F) \
 	git_attr_cache__push_file((R),(B),(F),GIT_ATTR_FILE_FROM_FILE,parse_ignore_file,(IGN),(S))
 
-struct ignores_walk_up_data {
-	git_ignores *ign;
-	git_error_state error;
-};
-
-static int push_one_ignore(void *ref, git_buf *path)
+static int push_one_ignore(void *payload, git_buf *path)
 {
-	struct ignores_walk_up_data *data = ref;
+	git_ignores *ign = payload;
 
-	return giterr_capture(
-		&data->error,
-		push_ignore_file(
-			data->ign->repo, data->ign, &data->ign->ign_path,
-			path->ptr, GIT_IGNORE_FILE) );
+	return push_ignore_file(
+		ign->repo, ign, &ign->ign_path, path->ptr, GIT_IGNORE_FILE);
 }
 
 static int get_internal_ignores(git_attr_file **ign, git_repository *repo)
@@ -142,13 +134,8 @@ int git_ignore__for_path(
 
 	/* load .gitignore up the path */
 	if (workdir != NULL) {
-		struct ignores_walk_up_data data = { ignores };
-
 		error = git_path_walk_up(
-			&ignores->dir, workdir, push_one_ignore, &data);
-
-		if (error == GIT_EUSER)
-			error = giterr_restore(&data.error);
+			&ignores->dir, workdir, push_one_ignore, ignores);
 		if (error < 0)
 			goto cleanup;
 	}
diff --git a/src/index.c b/src/index.c
index d0d2cf187..671bdfa79 100644
--- a/src/index.c
+++ b/src/index.c
@@ -2036,17 +2036,12 @@ int git_index_read_tree(git_index *index, const git_tree *tree)
 
 	error = git_tree_walk(tree, GIT_TREEWALK_POST, read_tree_cb, &data);
 
-	if (error == GIT_EUSER) {
-		giterr_set_oom();
-		git_vector_free(&entries);
-		return -1;
+	if (!error) {
+		git_vector_sort(&entries);
+		git_index_clear(index);
+		git_vector_swap(&entries, &index->entries);
 	}
 
-	git_vector_sort(&entries);
-
-	git_index_clear(index);
-
-	git_vector_swap(&entries, &index->entries);
 	git_vector_free(&entries);
 
 	return error;
@@ -2122,7 +2117,7 @@ int git_index_add_all(
 			if (error > 0) /* return > 0 means skip this one */
 				continue;
 			if (error < 0) { /* return < 0 means abort */
-				error = giterr_user_cancel();
+				GITERR_CALLBACK(error);
 				break;
 			}
 		}
@@ -2210,7 +2205,7 @@ static int index_apply_to_all(
 				continue;
 			}
 			if (error < 0) { /* return < 0 means abort */
-				error = giterr_user_cancel();
+				giterr_set_callback(error, "git_index_matched_path");
 				break;
 			}
 		}
diff --git a/src/indexer.c b/src/indexer.c
index d3253cb57..320845bd9 100644
--- a/src/indexer.c
+++ b/src/indexer.c
@@ -386,10 +386,10 @@ on_error:
 
 static int do_progress_callback(git_indexer *idx, git_transfer_progress *stats)
 {
-	if (idx->progress_cb &&
-		idx->progress_cb(stats, idx->progress_payload))
-		return giterr_user_cancel();
-
+	if (idx->progress_cb)
+		return giterr_set_callback(
+			idx->progress_cb(stats, idx->progress_payload),
+			"indexer progress");
 	return 0;
 }
 
@@ -495,7 +495,7 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 		processed = stats->indexed_objects = 0;
 		stats->total_objects = total_objects;
 
-		if ((error = do_progress_callback(idx, stats)) < 0)
+		if ((error = do_progress_callback(idx, stats)) != 0)
 			return error;
 	}
 
@@ -520,7 +520,7 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 				return 0;
 			}
 			if (error < 0)
-				return -1;
+				return error;
 
 			git_mwindow_close(&w);
 			idx->entry_start = entry_start;
@@ -533,7 +533,7 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 					return 0;
 				}
 				if (error < 0)
-					return -1;
+					return error;
 
 				idx->have_delta = 1;
 			} else {
@@ -578,7 +578,7 @@ int git_indexer_append(git_indexer *idx, const void *data, size_t size, git_tran
 		}
 		stats->received_objects++;
 
-		if ((error = do_progress_callback(idx, stats)) < 0)
+		if ((error = do_progress_callback(idx, stats)) != 0)
 			goto on_error;
 	}
 
diff --git a/src/merge.c b/src/merge.c
index d5bc6a39c..6f73fc14a 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -287,10 +287,8 @@ int git_repository_mergehead_foreach(
 		if ((error = git_oid_fromstr(&oid, line)) < 0)
 			goto cleanup;
 
-		if (cb(&oid, payload) != 0) {
-			error = giterr_user_cancel();
+		if ((error = GITERR_CALLBACK( cb(&oid, payload) )) != 0)
 			goto cleanup;
-		}
 
 		++line_num;
 	}
diff --git a/src/notes.c b/src/notes.c
index 7e8aecbae..e3a3fccf8 100644
--- a/src/notes.c
+++ b/src/notes.c
@@ -582,12 +582,10 @@ int git_note_foreach(
 	if ((error = git_note_iterator_new(&iter, repo, notes_ref)) < 0)
 		return error;
 
-	while (!(error = git_note_next(&note_id, &annotated_id, iter))) {
-		if (note_cb(&note_id, &annotated_id, payload)) {
-			error = giterr_user_cancel();
-			break;
-		}
-	}
+	while (!(error = git_note_next(&note_id, &annotated_id, iter)) &&
+		   !(error = GITERR_CALLBACK(
+				note_cb(&note_id, &annotated_id, payload))))
+		/* callback for each note */;
 
 	if (error == GIT_ITEROVER)
 		error = 0;
diff --git a/src/odb_loose.c b/src/odb_loose.c
index ae772b425..78cd792bd 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -547,8 +547,7 @@ static int locate_object_short_oid(
 	/* Explore directory to find a unique object matching short_oid */
 	error = git_path_direach(
 		object_location, 0, fn_locate_object_short_oid, &state);
-
-	if (error && error != GIT_EUSER)
+	if (error < 0 && error != GIT_EAMBIGUOUS)
 		return error;
 
 	if (!state.found)
@@ -696,7 +695,6 @@ struct foreach_state {
 	size_t dir_len;
 	git_odb_foreach_cb cb;
 	void *data;
-	git_error_state cb_error;
 };
 
 GIT_INLINE(int) filename_to_oid(git_oid *oid, const char *ptr)
@@ -735,19 +733,15 @@ static int foreach_object_dir_cb(void *_state, git_buf *path)
 	if (filename_to_oid(&oid, path->ptr + state->dir_len) < 0)
 		return 0;
 
-	if (state->cb(&oid, state->data))
-		return giterr_user_cancel();
-
-	return 0;
+	return giterr_set_callback(
+		state->cb(&oid, state->data), "git_odb_foreach");
 }
 
 static int foreach_cb(void *_state, git_buf *path)
 {
 	struct foreach_state *state = (struct foreach_state *) _state;
 
-	return giterr_capture(
-		&state->cb_error,
-		git_path_direach(path, 0, foreach_object_dir_cb, state));
+	return git_path_direach(path, 0, foreach_object_dir_cb, state);
 }
 
 static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb cb, void *data)
@@ -762,9 +756,10 @@ static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb
 
 	objects_dir = backend->objects_dir;
 
-	if (git_buf_sets(&buf, objects_dir) < 0)
-		return -1;
+	git_buf_sets(&buf, objects_dir);
 	git_path_to_dir(&buf);
+	if (git_buf_oom(&buf))
+		return -1;
 
 	memset(&state, 0, sizeof(state));
 	state.cb = cb;
@@ -773,9 +768,6 @@ static int loose_backend__foreach(git_odb_backend *_backend, git_odb_foreach_cb
 
 	error = git_path_direach(&buf, 0, foreach_cb, &state);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&state.cb_error);
-
 	git_buf_free(&buf);
 
 	return error;
diff --git a/src/odb_pack.c b/src/odb_pack.c
index 2c0319fb6..903b00d26 100644
--- a/src/odb_pack.c
+++ b/src/odb_pack.c
@@ -190,15 +190,9 @@ static int packfile_sort__cb(const void *a_, const void *b_)
 }
 
 
-struct packfile_load_data {
-	struct pack_backend *backend;
-	git_error_state error;
-};
-
-static int packfile_load__cb(void *_data, git_buf *path)
+static int packfile_load__cb(void *data, git_buf *path)
 {
-	struct packfile_load_data *data = _data;
-	struct pack_backend *backend = data->backend;
+	struct pack_backend *backend = data;
 	struct git_pack_file *pack;
 	const char *path_str = git_buf_cstr(path);
 	size_t i, cmp_len = git_buf_len(path);
@@ -227,7 +221,7 @@ static int packfile_load__cb(void *_data, git_buf *path)
 	if (!error)
 		error = git_vector_insert(&backend->packs, pack);
 
-	return giterr_capture(&data->error, error);
+	return error;
 
 }
 
@@ -328,32 +322,26 @@ static int pack_entry_find_prefix(
  * Implement the git_odb_backend API calls
  *
  ***********************************************************/
-static int pack_backend__refresh(git_odb_backend *backend)
+static int pack_backend__refresh(git_odb_backend *backend_)
 {
-	struct packfile_load_data data;
 	int error;
 	struct stat st;
 	git_buf path = GIT_BUF_INIT;
+	struct pack_backend *backend = (struct pack_backend *)backend_;
 
-	memset(&data, 0, sizeof(data));
-	data.backend = (struct pack_backend *)backend;
-
-	if (data.backend->pack_folder == NULL)
+	if (backend->pack_folder == NULL)
 		return 0;
 
-	if (p_stat(data.backend->pack_folder, &st) < 0 || !S_ISDIR(st.st_mode))
+	if (p_stat(backend->pack_folder, &st) < 0 || !S_ISDIR(st.st_mode))
 		return git_odb__error_notfound("failed to refresh packfiles", NULL);
 
-	git_buf_sets(&path, data.backend->pack_folder);
+	git_buf_sets(&path, backend->pack_folder);
 
 	/* reload all packs */
-	error = git_path_direach(&path, 0, packfile_load__cb, &data);
-
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
+	error = git_path_direach(&path, 0, packfile_load__cb, backend);
 
 	git_buf_free(&path);
-	git_vector_sort(&data.backend->packs);
+	git_vector_sort(&backend->packs);
 
 	return error;
 }
diff --git a/src/pack-objects.c b/src/pack-objects.c
index ac0615064..2f0007f4f 100644
--- a/src/pack-objects.c
+++ b/src/pack-objects.c
@@ -32,7 +32,6 @@ struct unpacked {
 struct tree_walk_context {
 	git_packbuilder *pb;
 	git_buf buf;
-	git_error_state error;
 };
 
 struct pack_write_context {
@@ -206,14 +205,18 @@ int git_packbuilder_insert(git_packbuilder *pb, const git_oid *oid,
 	po = pb->object_list + pb->nr_objects;
 	memset(po, 0x0, sizeof(*po));
 
-	if (git_odb_read_header(&po->size, &po->type, pb->odb, oid) < 0)
-		return -1;
+	if ((ret = git_odb_read_header(&po->size, &po->type, pb->odb, oid)) < 0)
+		return ret;
 
 	pb->nr_objects++;
 	git_oid_cpy(&po->id, oid);
 	po->hash = name_hash(name);
 
 	pos = kh_put(oid, pb->object_ix, &po->id, &ret);
+	if (ret < 0) {
+		giterr_set_oom();
+		return ret;
+	}
 	assert(ret != 0);
 	kh_value(pb->object_ix, pos) = po;
 
@@ -226,10 +229,9 @@ int git_packbuilder_insert(git_packbuilder *pb, const git_oid *oid,
 		if (elapsed >= MIN_PROGRESS_UPDATE_INTERVAL) {
 			pb->last_progress_report_time = current_time;
 
-			if (pb->progress_cb(
-					GIT_PACKBUILDER_ADDING_OBJECTS,
-					pb->nr_objects, 0, pb->progress_cb_payload))
-				return giterr_user_cancel();
+			return GITERR_CALLBACK( pb->progress_cb(
+				GIT_PACKBUILDER_ADDING_OBJECTS,
+				pb->nr_objects, 0, pb->progress_cb_payload) );
 		}
 	}
 
@@ -1303,7 +1305,7 @@ static int cb_tree_walk(
 		error = git_packbuilder_insert(
 			ctx->pb, git_tree_entry_id(entry), git_buf_cstr(&ctx->buf));
 
-	return giterr_capture(&ctx->error, error);
+	return error;
 }
 
 int git_packbuilder_insert_commit(git_packbuilder *pb, const git_oid *oid)
@@ -1331,9 +1333,6 @@ int git_packbuilder_insert_tree(git_packbuilder *pb, const git_oid *oid)
 	    !(error = git_packbuilder_insert(pb, oid, NULL)))
 		error = git_tree_walk(tree, GIT_TREEWALK_PRE, cb_tree_walk, &context);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&context.error);
-
 	git_tree_free(tree);
 	git_buf_free(&context.buf);
 	return error;
diff --git a/src/pack.c b/src/pack.c
index f69fe85e8..3f2adb2f3 100644
--- a/src/pack.c
+++ b/src/pack.c
@@ -1082,15 +1082,16 @@ int git_pack_foreach_entry(
 			git_vector_foreach(&offsets, i, current)
 				git_vector_insert(&oids, (void*)&current[4]);
 		}
+
 		git_vector_free(&offsets);
-		p->oids = (git_oid **)oids.contents;
+		p->oids = (git_oid **)git_vector_detach(NULL, NULL, &oids);
 	}
 
 	for (i = 0; i < p->num_objects; i++)
-		if (cb(p->oids[i], data))
-			return giterr_user_cancel();
+		if ((error = GITERR_CALLBACK( cb(p->oids[i], data) )) != 0)
+			break;
 
-	return 0;
+	return error;
 }
 
 static int pack_entry_find_offset(
diff --git a/src/path.c b/src/path.c
index 8be41c17e..857a2e61c 100644
--- a/src/path.c
+++ b/src/path.c
@@ -434,11 +434,11 @@ int git_path_walk_up(
 	iter.asize = path->asize;
 
 	while (scan >= stop) {
-		if (cb(data, &iter))
-			error = giterr_user_cancel();
+		error = GITERR_CALLBACK( cb(data, &iter) );
 		iter.ptr[scan] = oldc;
-		if (error < 0)
+		if (error)
 			break;
+
 		scan = git_buf_rfind_next(&iter, '/');
 		if (scan >= 0) {
 			scan++;
@@ -874,14 +874,12 @@ int git_path_direach(
 		if ((error = git_buf_put(path, de_path, de_len)) < 0)
 			break;
 
-		error = fn(arg, path);
+		error = GITERR_CALLBACK( fn(arg, path) );
 
 		git_buf_truncate(path, wd_len); /* restore path */
 
-		if (error) {
-			error = giterr_user_cancel();
+		if (error)
 			break;
-		}
 	}
 
 	closedir(dir);
diff --git a/src/path.h b/src/path.h
index 3daafd265..f26175d15 100644
--- a/src/path.h
+++ b/src/path.h
@@ -255,9 +255,10 @@ enum {
  * @param flags Combination of GIT_PATH_DIR flags.
  * @param callback Callback for each entry. Passed the `payload` and each
  *		successive path inside the directory as a full path.  This may
- *		safely append text to the pathbuf if needed.
+ *		safely append text to the pathbuf if needed.  Return non-zero to
+ *		cancel iteration (and return value will be propagated back).
  * @param payload Passed to callback as first argument.
- * @return 0 on success, GIT_EUSER on non-zero callback, or error code
+ * @return 0 on success or error code from OS error or from callback
  */
 extern int git_path_direach(
 	git_buf *pathbuf,
@@ -288,7 +289,7 @@ extern int git_path_cmp(
  *		original input path.
  * @param callback Function to invoke on each path.  Passed the `payload`
  *		and the buffer containing the current path.  The path should not
- *		be modified in any way.
+ *		be modified in any way. Return non-zero to stop iteration.
  * @param state Passed to fn as the first ath.
  */
 extern int git_path_walk_up(
diff --git a/src/push.c b/src/push.c
index a314922c1..428173397 100644
--- a/src/push.c
+++ b/src/push.c
@@ -659,8 +659,8 @@ int git_push_status_foreach(git_push *push,
 	unsigned int i;
 
 	git_vector_foreach(&push->status, i, status) {
-		if (cb(status->ref, status->msg, data) < 0)
-			return giterr_user_cancel();
+		GITERR_CHECK_ERROR(
+			GITERR_CALLBACK( cb(status->ref, status->msg, data) ) );
 	}
 
 	return 0;
diff --git a/src/refdb_fs.c b/src/refdb_fs.c
index 938e02a78..df7cb9d4d 100644
--- a/src/refdb_fs.c
+++ b/src/refdb_fs.c
@@ -264,14 +264,9 @@ done:
 	return error;
 }
 
-struct packed_loadloose_data {
-	refdb_fs_backend *backend;
-	git_error_state error;
-};
-
-static int _dirent_loose_load(void *data_, git_buf *full_path)
+static int _dirent_loose_load(void *payload, git_buf *full_path)
 {
-	struct packed_loadloose_data *data = data_;
+	refdb_fs_backend *backend = payload;
 	const char *file_path;
 
 	if (git__suffixcmp(full_path->ptr, ".lock") == 0)
@@ -279,12 +274,11 @@ static int _dirent_loose_load(void *data_, git_buf *full_path)
 
 	if (git_path_isdir(full_path->ptr))
 		return git_path_direach(
-			full_path, data->backend->direach_flags, _dirent_loose_load, data);
+			full_path, backend->direach_flags, _dirent_loose_load, backend);
 
-	file_path = full_path->ptr + strlen(data->backend->path);
+	file_path = full_path->ptr + strlen(backend->path);
 
-	return giterr_capture(
-		&data->error, loose_lookup_to_packfile(data->backend, file_path));
+	return loose_lookup_to_packfile(backend, file_path);
 }
 
 /*
@@ -297,27 +291,20 @@ static int packed_loadloose(refdb_fs_backend *backend)
 {
 	int error;
 	git_buf refs_path = GIT_BUF_INIT;
-	struct packed_loadloose_data data;
 
 	if (git_buf_joinpath(&refs_path, backend->path, GIT_REFS_DIR) < 0)
 		return -1;
 
-	memset(&data, 0, sizeof(data));
-	data.backend = backend;
-
 	/*
 	 * Load all the loose files from disk into the Packfile table.
 	 * This will overwrite any old packed entries with their
 	 * updated loose versions
 	 */
 	error = git_path_direach(
-		&refs_path, backend->direach_flags, _dirent_loose_load, &data);
+		&refs_path, backend->direach_flags, _dirent_loose_load, backend);
 
 	git_buf_free(&refs_path);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
-
 	return error;
 }
 
diff --git a/src/refs.c b/src/refs.c
index 60ed9ffb1..afb067986 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -516,12 +516,9 @@ int git_reference_foreach(
 	if ((error = git_reference_iterator_new(&iter, repo)) < 0)
 		return error;
 
-	while ((error = git_reference_next(&ref, iter)) == 0) {
-		if (callback(ref, payload)) {
-			error = giterr_user_cancel();
-			break;
-		}
-	}
+	while (!(error = git_reference_next(&ref, iter)) &&
+		   !(error = GITERR_CALLBACK( callback(ref, payload) )))
+		/* callback on each reference */;
 
 	if (error == GIT_ITEROVER)
 		error = 0;
@@ -542,12 +539,9 @@ int git_reference_foreach_name(
 	if ((error = git_reference_iterator_new(&iter, repo)) < 0)
 		return error;
 
-	while ((error = git_reference_next_name(&refname, iter)) == 0) {
-		if (callback(refname, payload)) {
-			error = giterr_user_cancel();
-			break;
-		}
-	}
+	while (!(error = git_reference_next_name(&refname, iter)) &&
+		   !(error = GITERR_CALLBACK( callback(refname, payload) )))
+		/* callback on each reference name */;
 
 	if (error == GIT_ITEROVER)
 		error = 0;
@@ -569,12 +563,9 @@ int git_reference_foreach_glob(
 	if ((error = git_reference_iterator_glob_new(&iter, repo, glob)) < 0)
 		return error;
 
-	while ((error = git_reference_next_name(&refname, iter)) == 0) {
-		if (callback(refname, payload)) {
-			error = giterr_user_cancel();
-			break;
-		}
-	}
+	while (!(error = git_reference_next_name(&refname, iter)) &&
+		   !(error = GITERR_CALLBACK( callback(refname, payload) )))
+		/* callback on each matching reference name */;
 
 	if (error == GIT_ITEROVER)
 		error = 0;
@@ -621,7 +612,9 @@ void git_reference_iterator_free(git_reference_iterator *iter)
 
 static int cb__reflist_add(const char *ref, void *data)
 {
-	return git_vector_insert((git_vector *)data, git__strdup(ref));
+	char *name = git__strdup(ref);
+	GITERR_CHECK_ALLOC(name);
+	return git_vector_insert((git_vector *)data, name);
 }
 
 int git_reference_list(
@@ -644,8 +637,8 @@ int git_reference_list(
 		return -1;
 	}
 
-	array->strings = (char **)ref_list.contents;
-	array->count = ref_list.length;
+	array->strings = (char **)git_vector_detach(&array->count, NULL, &ref_list);
+
 	return 0;
 }
 
diff --git a/src/remote.c b/src/remote.c
index 93d243001..307306d1a 100644
--- a/src/remote.c
+++ b/src/remote.c
@@ -251,14 +251,12 @@ int git_remote_create_inmemory(git_remote **out, git_repository *repo, const cha
 struct refspec_cb_data {
 	git_remote *remote;
 	int fetch;
-	git_error_state error;
 };
 
 static int refspec_cb(const git_config_entry *entry, void *payload)
 {
 	struct refspec_cb_data *data = (struct refspec_cb_data *)payload;
-	return giterr_capture(
-		&data->error, add_refspec(data->remote, entry->value, data->fetch));
+	return add_refspec(data->remote, entry->value, data->fetch);
 }
 
 static int get_optional_config(
@@ -316,17 +314,15 @@ int git_remote_load(git_remote **out, git_repository *repo, const char *name)
 	if ((error = get_check_cert(&remote->check_cert, repo)) < 0)
 		goto cleanup;
 
-	if ((git_vector_init(&remote->refs, 32, NULL) < 0) ||
-	    (git_vector_init(&remote->refspecs, 2, NULL) < 0) ||
-	    (git_vector_init(&remote->active_refspecs, 2, NULL) < 0)) {
+	if (git_vector_init(&remote->refs, 32, NULL) < 0 ||
+	    git_vector_init(&remote->refspecs, 2, NULL) < 0 ||
+	    git_vector_init(&remote->active_refspecs, 2, NULL) < 0) {
 		error = -1;
 		goto cleanup;
 	}
 
-	if (git_buf_printf(&buf, "remote.%s.url", name) < 0) {
-		error = -1;
+	if ((error = git_buf_printf(&buf, "remote.%s.url", name)) < 0)
 		goto cleanup;
-	}
 
 	if ((error = get_optional_config(&found, config, &buf, NULL, (void *)&val)) < 0)
 		goto cleanup;
@@ -387,9 +383,6 @@ int git_remote_load(git_remote **out, git_repository *repo, const char *name)
 cleanup:
 	git_buf_free(&buf);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
-
 	if (error < 0)
 		git_remote_free(remote);
 
@@ -636,7 +629,7 @@ int git_remote_connect(git_remote *remote, git_direction direction)
 	if (!remote->check_cert)
 		flags |= GIT_TRANSPORTFLAGS_NO_CHECK_CERT;
 
-	if ((error = t->connect(t, url, remote->callbacks.credentials, remote->callbacks.payload, direction, flags)) < 0)
+	if ((error = t->connect(t, url, remote->callbacks.credentials, remote->callbacks.payload, direction, flags)) != 0)
 		goto on_error;
 
 	remote->transport = t;
@@ -788,7 +781,7 @@ int git_remote_download(git_remote *remote)
 	git_vector_free(&refs);
 
 	if (error < 0)
-		return -1;
+		return error;
 
 	if ((error = git_fetch_negotiate(remote)) < 0)
 		return error;
@@ -801,10 +794,10 @@ int git_remote_fetch(git_remote *remote)
 	int error;
 
 	/* Connect and download everything */
-	if ((error = git_remote_connect(remote, GIT_DIRECTION_FETCH)) < 0)
+	if ((error = git_remote_connect(remote, GIT_DIRECTION_FETCH)) != 0)
 		return error;
 
-	if ((error = git_remote_download(remote)) < 0)
+	if ((error = git_remote_download(remote)) != 0)
 		return error;
 
 	/* We don't need to be connected anymore */
@@ -1032,7 +1025,6 @@ int git_remote_update_tips(git_remote *remote)
 	int error;
 	size_t i;
 
-
 	if (git_refspec__parse(&tagspec, GIT_REFSPEC_TAGS, true) < 0)
 		return -1;
 
@@ -1112,14 +1104,9 @@ void git_remote_free(git_remote *remote)
 	git__free(remote);
 }
 
-struct remote_list_data {
-	git_vector list;
-	git_error_state error;
-};
-
 static int remote_list_cb(const git_config_entry *entry, void *payload)
 {
-	struct remote_list_data *data = payload;
+	git_vector *list = payload;
 	const char *name = entry->name + strlen("remote.");
 	size_t namelen = strlen(name);
 	char *remote_name;
@@ -1130,42 +1117,35 @@ static int remote_list_cb(const git_config_entry *entry, void *payload)
 		remote_name = git__strndup(name, namelen - 4); /* strip ".url" */
 	else
 		remote_name = git__strndup(name, namelen - 8); /* strip ".pushurl" */
-	if (!remote_name)
-		return giterr_capture(&data->error, -1);
+	GITERR_CHECK_ALLOC(remote_name);
 
-	return giterr_capture(
-		&data->error, git_vector_insert(&data->list, remote_name));
+	return git_vector_insert(list, remote_name);
 }
 
 int git_remote_list(git_strarray *remotes_list, git_repository *repo)
 {
 	int error;
 	git_config *cfg;
-	struct remote_list_data data;
+	git_vector list = GIT_VECTOR_INIT;
 
 	if ((error = git_repository_config__weakptr(&cfg, repo)) < 0)
 		return error;
 
-	memset(&data, 0, sizeof(data));
-	if ((error = git_vector_init(&data.list, 4, git__strcmp_cb)) < 0)
+	if ((error = git_vector_init(&list, 4, git__strcmp_cb)) < 0)
 		return error;
 
 	error = git_config_foreach_match(
-		cfg, "^remote\\..*\\.(push)?url$", remote_list_cb, &data);
-
-	/* cb error is converted to GIT_EUSER by git_config_foreach */
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
+		cfg, "^remote\\..*\\.(push)?url$", remote_list_cb, &list);
 
 	if (error < 0) {
-		git_vector_free_all(&data.list);
+		git_vector_free_all(&list);
 		return error;
 	}
 
-	git_vector_uniq(&data.list, git__free);
+	git_vector_uniq(&list, git__free);
 
-	remotes_list->strings = (char **)data.list.contents;
-	remotes_list->count = data.list.length;
+	remotes_list->strings =
+		(char **)git_vector_detach(&remotes_list->count, NULL, &list);
 
 	return 0;
 }
@@ -1256,7 +1236,6 @@ struct update_data {
 	git_config *config;
 	const char *old_remote_name;
 	const char *new_remote_name;
-	git_error_state error;
 };
 
 static int update_config_entries_cb(
@@ -1268,9 +1247,8 @@ static int update_config_entries_cb(
 	if (strcmp(entry->value, data->old_remote_name))
 		return 0;
 
-	return giterr_capture(
-		&data->error, git_config_set_string(
-			data->config, entry->name, data->new_remote_name));
+	return git_config_set_string(
+		data->config, entry->name, data->new_remote_name);
 }
 
 static int update_branch_remote_config_entry(
@@ -1287,13 +1265,8 @@ static int update_branch_remote_config_entry(
 	data.old_remote_name = old_name;
 	data.new_remote_name = new_name;
 
-	error = git_config_foreach_match(
+	return git_config_foreach_match(
 		data.config, "branch\\..+\\.remote", update_config_entries_cb, &data);
-
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
-
-	return error;
 }
 
 static int rename_one_remote_reference(
@@ -1357,13 +1330,14 @@ static int rename_fetch_refspecs(
 	git_buf base = GIT_BUF_INIT, var = GIT_BUF_INIT, val = GIT_BUF_INIT;
 	const git_refspec *spec;
 	size_t i;
-	int error = -1;
-
-	if (git_buf_printf(&base, "+refs/heads/*:refs/remotes/%s/*", remote->name) < 0)
-		goto cleanup;
+	int error = 0;
 
 	if ((error = git_repository_config__weakptr(&config, remote->repo)) < 0)
-		goto cleanup;
+		return error;
+
+	if ((error = git_buf_printf(
+			&base, "+refs/heads/*:refs/remotes/%s/*", remote->name)) < 0)
+		return error;
 
 	git_vector_foreach(&remote->refspecs, i, spec) {
 		if (spec->push)
@@ -1374,10 +1348,9 @@ static int rename_fetch_refspecs(
 		if (!remote->name ||
 			strcmp(git_buf_cstr(&base), spec->string)) {
 
-			if (callback(spec->string, payload) < 0) {
-				error = giterr_user_cancel();
-				goto cleanup;
-			}
+			error = GITERR_CALLBACK( callback(spec->string, payload) );
+			if (error)
+				break;
 			continue;
 		}
 
@@ -1391,15 +1364,14 @@ static int rename_fetch_refspecs(
 			git_buf_printf(&var, "remote.%s.fetch", new_name) < 0)
 		{
 			error = -1;
-			goto cleanup;
+			break;
 		}
 
 		if ((error = git_config_set_string(
 				config, git_buf_cstr(&var), git_buf_cstr(&val))) < 0)
-			goto cleanup;
+			break;
 	}
 
-cleanup:
 	git_buf_free(&base);
 	git_buf_free(&var);
 	git_buf_free(&val);
diff --git a/src/repository.c b/src/repository.c
index 443744504..94f6603aa 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -1608,15 +1608,14 @@ static int at_least_one_cb(const char *refname, void *payload)
 {
 	GIT_UNUSED(refname);
 	GIT_UNUSED(payload);
-
-	return GIT_EUSER;
+	return GIT_PASSTHROUGH;
 }
 
 static int repo_contains_no_reference(git_repository *repo)
 {
 	int error = git_reference_foreach_name(repo, &at_least_one_cb, NULL);
 
-	if (error == GIT_EUSER)
+	if (error == GIT_PASSTHROUGH)
 		return 0;
 
 	if (!error)
diff --git a/src/revwalk.c b/src/revwalk.c
index e8c7f23ec..c0a053211 100644
--- a/src/revwalk.c
+++ b/src/revwalk.c
@@ -169,15 +169,12 @@ static int push_ref(git_revwalk *walk, const char *refname, int hide)
 struct push_cb_data {
 	git_revwalk *walk;
 	int hide;
-	git_error_state error;
 };
 
 static int push_glob_cb(const char *refname, void *data_)
 {
 	struct push_cb_data *data = (struct push_cb_data *)data_;
-
-	return giterr_capture(
-		&data->error, push_ref(data->walk, refname, data->hide) );
+	return push_ref(data->walk, refname, data->hide);
 }
 
 static int push_glob(git_revwalk *walk, const char *glob, int hide)
@@ -204,12 +201,9 @@ static int push_glob(git_revwalk *walk, const char *glob, int hide)
 
 	data.walk = walk;
 	data.hide = hide;
-	memset(&data.error, 0, sizeof(data.error));
 
 	error = git_reference_foreach_glob(
 		walk->repo, git_buf_cstr(&buf), push_glob_cb, &data);
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
 
 	git_buf_free(&buf);
 	return error;
diff --git a/src/stash.c b/src/stash.c
index 06a7b9a33..458a1e175 100644
--- a/src/stash.c
+++ b/src/stash.c
@@ -440,7 +440,7 @@ static int is_dirty_cb(const char *path, unsigned int status, void *payload)
 	GIT_UNUSED(status);
 	GIT_UNUSED(payload);
 
-	return 1;
+	return GIT_PASSTHROUGH;
 }
 
 static int ensure_there_are_changes_to_stash(
@@ -463,7 +463,7 @@ static int ensure_there_are_changes_to_stash(
 
 	error = git_status_foreach_ext(repo, &opts, is_dirty_cb, NULL);
 
-	if (error == GIT_EUSER)
+	if (error == GIT_PASSTHROUGH)
 		return 0;
 
 	if (!error)
@@ -582,13 +582,13 @@ int git_stash_foreach(
 	for (i = 0; i < max; i++) {
 		entry = git_reflog_entry_byindex(reflog, i);
 
-		if (callback(i,
-			git_reflog_entry_message(entry),
-			git_reflog_entry_id_new(entry),
-			payload)) {
-			error = giterr_user_cancel();
+		error = GITERR_CALLBACK(
+			callback(i,
+				git_reflog_entry_message(entry),
+				git_reflog_entry_id_new(entry),
+				payload) );
+		if (error)
 			break;
-		}
 	}
 
 cleanup:
diff --git a/src/status.c b/src/status.c
index ce571a2d8..d76617a72 100644
--- a/src/status.c
+++ b/src/status.c
@@ -152,32 +152,25 @@ static git_status_t status_compute(
 	return st;
 }
 
-struct status_data {
-	git_status_list *status;
-	git_error_state err;
-};
-
 static int status_collect(
 	git_diff_delta *head2idx,
 	git_diff_delta *idx2wd,
 	void *payload)
 {
-	struct status_data *data = payload;
+	git_status_list *status = payload;
 	git_status_entry *status_entry;
 
-	if (!status_is_included(data->status, head2idx, idx2wd))
+	if (!status_is_included(status, head2idx, idx2wd))
 		return 0;
 
 	status_entry = git__malloc(sizeof(git_status_entry));
-	if (!status_entry)
-		return giterr_capture(&data->err, -1);
+	GITERR_CHECK_ALLOC(status_entry);
 
-	status_entry->status = status_compute(data->status, head2idx, idx2wd);
+	status_entry->status = status_compute(status, head2idx, idx2wd);
 	status_entry->head_to_index = head2idx;
 	status_entry->index_to_workdir = idx2wd;
 
-	return giterr_capture(
-		&data->err, git_vector_insert(&data->status->paired, status_entry));
+	return git_vector_insert(&status->paired, status_entry);
 }
 
 GIT_INLINE(int) status_entry_cmp_base(
@@ -321,18 +314,10 @@ int git_status_list_new(
 			goto done;
 	}
 
-	{
-		struct status_data data = { 0 };
-		data.status = status;
-
-		error = git_diff__paired_foreach(
-			status->head2idx, status->idx2wd, status_collect, &data);
-
-		if (error == GIT_EUSER)
-			error = giterr_restore(&data.err);
-		if (error < 0)
-			goto done;
-	}
+	error = git_diff__paired_foreach(
+		status->head2idx, status->idx2wd, status_collect, status);
+	if (error < 0)
+		goto done;
 
 	if (flags & GIT_STATUS_OPT_SORT_CASE_SENSITIVELY)
 		git_vector_set_cmp(&status->paired, status_entry_cmp);
@@ -407,10 +392,9 @@ int git_status_foreach_ext(
 			status_entry->head_to_index->old_file.path :
 			status_entry->index_to_workdir->old_file.path;
 
-		if (cb(path, status_entry->status, payload) != 0) {
-			error = giterr_user_cancel();
+		error = GITERR_CALLBACK( cb(path, status_entry->status, payload) );
+		if (error)
 			break;
-		}
 	}
 
 	git_status_list_free(status);
diff --git a/src/submodule.c b/src/submodule.c
index 15c87c0b4..e9d534ae8 100644
--- a/src/submodule.c
+++ b/src/submodule.c
@@ -71,11 +71,6 @@ __KHASH_IMPL(
 	str, static kh_inline, const char *, void *, 1,
 	str_hash_no_trailing_slash, str_equal_no_trailing_slash);
 
-struct submodule_callback_payload {
-	git_repository *repo;
-	git_error_state error;
-};
-
 static int load_submodule_config(git_repository *repo);
 static git_config_backend *open_gitmodules(git_repository *, bool, const git_oid *);
 static int lookup_head_remote(git_buf *url, git_repository *repo);
@@ -173,10 +168,8 @@ int git_submodule_foreach(
 				break;
 		}
 
-		if (callback(sm, sm->name, payload)) {
-			error = giterr_user_cancel();
+		if ((error = GITERR_CALLBACK(callback(sm, sm->name, payload))) != 0)
 			break;
-		}
 	});
 
 	git_vector_free(&seen);
@@ -825,7 +818,6 @@ int git_submodule_reload(git_submodule *submodule)
 {
 	int error = 0;
 	git_config_backend *mods;
-	struct submodule_callback_payload p;
 
 	assert(submodule);
 
@@ -838,9 +830,6 @@ int git_submodule_reload(git_submodule *submodule)
 		return error;
 
 	/* refresh config data */
-	memset(&p, 0, sizeof(p));
-	p.repo = submodule->repo;
-
 	mods = open_gitmodules(submodule->repo, false, NULL);
 	if (mods != NULL) {
 		git_buf path = GIT_BUF_INIT;
@@ -851,13 +840,9 @@ int git_submodule_reload(git_submodule *submodule)
 
 		if (git_buf_oom(&path))
 			error = -1;
-		else {
+		else
 			error = git_config_file_foreach_match(
-				mods, path.ptr, submodule_load_from_config, &p);
-
-			if (error == GIT_EUSER)
-				error = giterr_restore(&p.error);
-		}
+				mods, path.ptr, submodule_load_from_config, submodule->repo);
 
 		git_buf_free(&path);
 		git_config_file_free(mods);
@@ -867,15 +852,11 @@ int git_submodule_reload(git_submodule *submodule)
 	}
 
 	/* refresh wd data */
-
 	submodule->flags = submodule->flags &
 		~(GIT_SUBMODULE_STATUS_IN_WD | GIT_SUBMODULE_STATUS__WD_OID_VALID);
 
-	error = submodule_load_from_wd_lite(submodule, submodule->path, &p);
-	if (error)
-		error = giterr_restore(&p.error);
-
-	return error;
+	return submodule_load_from_wd_lite(
+		submodule, submodule->path, submodule->repo);
 }
 
 static void submodule_copy_oid_maybe(
@@ -1100,8 +1081,8 @@ int git_submodule_parse_update(git_submodule_update_t *out, const char *value)
 static int submodule_load_from_config(
 	const git_config_entry *entry, void *payload)
 {
-	struct submodule_callback_payload *p = payload;
-	git_strmap *smcfg = p->repo->submodules;
+	git_repository *repo = payload;
+	git_strmap *smcfg = repo->submodules;
 	const char *namestart, *property, *alternate = NULL;
 	const char *key = entry->name, *value = entry->value, *path;
 	git_buf name = GIT_BUF_INIT;
@@ -1121,7 +1102,7 @@ static int submodule_load_from_config(
 	path = !strcasecmp(property, "path") ? value : NULL;
 
 	if ((error = git_buf_set(&name, namestart, property - namestart - 1)) < 0 ||
-		(error = submodule_get(&sm, p->repo, name.ptr, path)) < 0)
+		(error = submodule_get(&sm, repo, name.ptr, path)) < 0)
 		goto done;
 
 	sm->flags |= GIT_SUBMODULE_STATUS_IN_CONFIG;
@@ -1197,22 +1178,21 @@ static int submodule_load_from_config(
 
 done:
 	git_buf_free(&name);
-	return giterr_capture(&p->error, error);
+	return error;
 }
 
 static int submodule_load_from_wd_lite(
 	git_submodule *sm, const char *name, void *payload)
 {
-	struct submodule_callback_payload *p = payload;
 	git_buf path = GIT_BUF_INIT;
 
-	GIT_UNUSED(name);
+	GIT_UNUSED(name); GIT_UNUSED(payload);
 
 	if (git_repository_is_bare(sm->repo))
 		return 0;
 
 	if (git_buf_joinpath(&path, git_repository_workdir(sm->repo), sm->path) < 0)
-		return giterr_capture(&p->error, -1);
+		return -1;
 
 	if (git_path_isdir(path.ptr))
 		sm->flags |= GIT_SUBMODULE_STATUS__WD_SCANNED;
@@ -1355,14 +1335,11 @@ static int load_submodule_config(git_repository *repo)
 	int error;
 	git_oid gitmodules_oid;
 	git_config_backend *mods = NULL;
-	struct submodule_callback_payload p;
 
 	if (repo->submodules)
 		return 0;
 
 	memset(&gitmodules_oid, 0, sizeof(gitmodules_oid));
-	memset(&p, 0, sizeof(p));
-	p.repo = repo;
 
 	/* Submodule data is kept in a hashtable keyed by both name and path.
 	 * These are usually the same, but that is not guaranteed.
@@ -1386,21 +1363,18 @@ static int load_submodule_config(git_repository *repo)
 
 	if ((mods = open_gitmodules(repo, false, &gitmodules_oid)) != NULL &&
 		(error = git_config_file_foreach(
-			mods, submodule_load_from_config, &p)) < 0)
+			mods, submodule_load_from_config, repo)) < 0)
 		goto cleanup;
 
 	/* shallow scan submodules in work tree */
 
 	if (!git_repository_is_bare(repo))
-		error = git_submodule_foreach(repo, submodule_load_from_wd_lite, &p);
+		error = git_submodule_foreach(repo, submodule_load_from_wd_lite, NULL);
 
 cleanup:
 	if (mods != NULL)
 		git_config_file_free(mods);
 
-	if (error == GIT_EUSER)
-		error = giterr_restore(&p.error);
-
 	if (error)
 		git_submodule_config_free(repo);
 
diff --git a/src/tag.c b/src/tag.c
index 5d4e45e5d..adf2819d7 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -414,7 +414,6 @@ typedef struct {
 	git_repository *repo;
 	git_tag_foreach_cb cb;
 	void *cb_data;
-	git_error_state error;
 } tag_cb_data;
 
 static int tags_cb(const char *ref, void *data)
@@ -427,16 +426,15 @@ static int tags_cb(const char *ref, void *data)
 		return 0; /* no tag */
 
 	if (!(error = git_reference_name_to_id(&oid, d->repo, ref))) {
-		if (d->cb(ref, &oid, d->cb_data))
-			error = giterr_user_cancel();
+		error = d->cb(ref, &oid, d->cb_data);
+		giterr_set_callback(error, "git_tag_foreach");
 	}
 
-	return giterr_capture(&d->error, error);
+	return error;
 }
 
 int git_tag_foreach(git_repository *repo, git_tag_foreach_cb cb, void *cb_data)
 {
-	int error;
 	tag_cb_data data;
 
 	assert(repo && cb);
@@ -444,14 +442,8 @@ int git_tag_foreach(git_repository *repo, git_tag_foreach_cb cb, void *cb_data)
 	data.cb = cb;
 	data.cb_data = cb_data;
 	data.repo = repo;
-	memset(&data.error, 0, sizeof(data.error));
-
-	error = git_reference_foreach_name(repo, &tags_cb, &data);
-
-	if (error == GIT_EUSER)
-		error = giterr_restore(&data.error);
 
-	return error;
+	return git_reference_foreach_name(repo, &tags_cb, &data);
 }
 
 typedef struct {
@@ -470,8 +462,8 @@ static int tag_list_cb(const char *tag_name, git_oid *oid, void *data)
 		p_fnmatch(filter->pattern, tag_name + GIT_REFS_TAGS_DIR_LEN, 0) == 0)
 	{
 		char *matched = git__strdup(tag_name + GIT_REFS_TAGS_DIR_LEN);
-		if (!matched)
-			return -1;
+		GITERR_CHECK_ALLOC(matched);
+
 		return git_vector_insert(filter->taglist, matched);
 	}
 
@@ -494,19 +486,12 @@ int git_tag_list_match(git_strarray *tag_names, const char *pattern, git_reposit
 
 	error = git_tag_foreach(repo, &tag_list_cb, (void *)&filter);
 
-	/* the only case where callback will return an error is oom */
-	if (error == GIT_EUSER) {
-		giterr_set_oom();
-		error = -1;
-	}
-
-	if (error < 0) {
+	if (error < 0)
 		git_vector_free(&taglist);
-		return error;
-	}
 
-	tag_names->strings = (char **)taglist.contents;
-	tag_names->count = taglist.length;
+	tag_names->strings =
+		(char **)git_vector_detach(&tag_names->count, NULL, &taglist);
+
 	return 0;
 }
 
diff --git a/src/transports/http.c b/src/transports/http.c
index ace0d97d0..0e1bbf60d 100644
--- a/src/transports/http.c
+++ b/src/transports/http.c
@@ -382,9 +382,6 @@ static int on_body_fill_buffer(http_parser *parser, const char *str, size_t len)
 
 static void clear_parser_state(http_subtransport *t)
 {
-	unsigned i;
-	char *entry;
-
 	http_parser_init(&t->parser, HTTP_RESPONSE);
 	gitno_buffer_setup(&t->socket,
 		&t->parse_buffer,
@@ -407,10 +404,7 @@ static void clear_parser_state(http_subtransport *t)
 	git__free(t->location);
 	t->location = NULL;
 
-	git_vector_foreach(&t->www_authenticate, i, entry)
-		git__free(entry);
-
-	git_vector_free(&t->www_authenticate);
+	git_vector_free_all(&t->www_authenticate);
 }
 
 static int write_chunk(gitno_socket *socket, const char *buffer, size_t len)
diff --git a/src/transports/local.c b/src/transports/local.c
index f09e797ce..4635d5dd3 100644
--- a/src/transports/local.c
+++ b/src/transports/local.c
@@ -43,43 +43,43 @@ typedef struct {
 static int add_ref(transport_local *t, const char *name)
 {
 	const char peeled[] = "^{}";
+	git_oid head_oid;
 	git_remote_head *head;
 	git_object *obj = NULL, *target = NULL;
 	git_buf buf = GIT_BUF_INIT;
 	int error;
 
-	head = git__calloc(1, sizeof(git_remote_head));
-	GITERR_CHECK_ALLOC(head);
-
-	head->name = git__strdup(name);
-	GITERR_CHECK_ALLOC(head->name);
-
-	error = git_reference_name_to_id(&head->oid, t->repo, name);
+	error = git_reference_name_to_id(&head_oid, t->repo, name);
 	if (error < 0) {
-		git__free(head->name);
-		git__free(head);
 		if (!strcmp(name, GIT_HEAD_FILE) && error == GIT_ENOTFOUND) {
-			/* This is actually okay.  Empty repos often have a HEAD that points to
-			 * a nonexistent "refs/heads/master". */
+			/* This is actually okay.  Empty repos often have a HEAD that
+			 * points to a nonexistent "refs/heads/master". */
 			giterr_clear();
 			return 0;
 		}
 		return error;
 	}
 
-	if (git_vector_insert(&t->refs, head) < 0)
-	{
+	head = git__calloc(1, sizeof(git_remote_head));
+	GITERR_CHECK_ALLOC(head);
+
+	head->name = git__strdup(name);
+	GITERR_CHECK_ALLOC(head->name);
+
+	git_oid_cpy(&head->oid, &head_oid);
+
+	if ((error = git_vector_insert(&t->refs, head)) < 0) {
 		git__free(head->name);
 		git__free(head);
-		return -1;
+		return error;
 	}
 
 	/* If it's not a tag, we don't need to try to peel it */
 	if (git__prefixcmp(name, GIT_REFS_TAGS_DIR))
 		return 0;
 
-	if (git_object_lookup(&obj, t->repo, &head->oid, GIT_OBJ_ANY) < 0)
-		return -1;
+	if ((error = git_object_lookup(&obj, t->repo, &head->oid, GIT_OBJ_ANY)) < 0)
+		return error;
 
 	head = NULL;
 
@@ -94,27 +94,24 @@ static int add_ref(transport_local *t, const char *name)
 	/* And if it's a tag, peel it, and add it to the list */
 	head = git__calloc(1, sizeof(git_remote_head));
 	GITERR_CHECK_ALLOC(head);
+
 	if (git_buf_join(&buf, 0, name, peeled) < 0)
 		return -1;
-
 	head->name = git_buf_detach(&buf);
 
-	if (git_tag_peel(&target, (git_tag *) obj) < 0)
-		goto on_error;
+	if (!(error = git_tag_peel(&target, (git_tag *)obj))) {
+		git_oid_cpy(&head->oid, git_object_id(target));
 
-	git_oid_cpy(&head->oid, git_object_id(target));
-	git_object_free(obj);
-	git_object_free(target);
-
-	if (git_vector_insert(&t->refs, head) < 0)
-		return -1;
-
-	return 0;
+		if ((error = git_vector_insert(&t->refs, head)) < 0) {
+			git__free(head->name);
+			git__free(head);
+		}
+	}
 
-on_error:
 	git_object_free(obj);
 	git_object_free(target);
-	return -1;
+
+	return error;
 }
 
 static int store_refs(transport_local *t)
@@ -222,7 +219,7 @@ static int local_ls(const git_remote_head ***out, size_t *size, git_transport *t
 		return -1;
 	}
 
-	*out = (const git_remote_head **) t->refs.contents;
+	*out = (const git_remote_head **)t->refs.contents;
 	*size = t->refs.length;
 
 	return 0;
@@ -529,7 +526,7 @@ static int local_download_pack(
 		}
 	}
 
-	if ((error = git_odb_write_pack(&writepack, odb, progress_cb, progress_payload)) < 0)
+	if ((error = git_odb_write_pack(&writepack, odb, progress_cb, progress_payload)) != 0)
 		goto cleanup;
 
 	/* Write the data to the ODB */
@@ -540,7 +537,7 @@ static int local_download_pack(
 		data.progress_payload = progress_payload;
 		data.writepack = writepack;
 
-		if ((error = git_packbuilder_foreach(pack, foreach_cb, &data)) < 0)
+		if ((error = git_packbuilder_foreach(pack, foreach_cb, &data)) != 0)
 			goto cleanup;
 	}
 	error = writepack->commit(writepack, stats);
diff --git a/src/transports/smart.c b/src/transports/smart.c
index e298f3510..69eaf9b78 100644
--- a/src/transports/smart.c
+++ b/src/transports/smart.c
@@ -23,12 +23,13 @@ static int git_smart__recv_cb(gitno_buffer *buf)
 
 	buf->offset += bytes_read;
 
-	if (t->packetsize_cb && !t->cancelled.val)
-		if (t->packetsize_cb(bytes_read, t->packetsize_payload)) {
+	if (t->packetsize_cb && !t->cancelled.val) {
+		error = t->packetsize_cb(bytes_read, t->packetsize_payload);
+		if (error) {
 			git_atomic_set(&t->cancelled, 1);
-
-			return giterr_user_cancel();
+			return GIT_EUSER;
 		}
+	}
 
 	return (int)(buf->offset - old_len);
 }
@@ -341,7 +342,7 @@ int git_transport_smart(git_transport **out, git_remote *owner, void *param)
 	t->parent.is_connected = git_smart__is_connected;
 	t->parent.read_flags = git_smart__read_flags;
 	t->parent.cancel = git_smart__cancel;
-	
+
 	t->owner = owner;
 	t->rpc = definition->rpc;
 
@@ -358,7 +359,7 @@ int git_transport_smart(git_transport **out, git_remote *owner, void *param)
 	if (definition->callback(&t->wrapped, &t->parent) < 0) {
 		git__free(t);
 		return -1;
-	}	
+	}
 
 	*out = (git_transport *) t;
 	return 0;
diff --git a/src/transports/smart_protocol.c b/src/transports/smart_protocol.c
index a4046ee43..dd9b5e0ed 100644
--- a/src/transports/smart_protocol.c
+++ b/src/transports/smart_protocol.c
@@ -45,7 +45,7 @@ int git_smart__store_refs(transport_smart *t, int flushes)
 			error = GIT_EBUFS;
 
 		if (error < 0 && error != GIT_EBUFS)
-			return -1;
+			return error;
 
 		if (error == GIT_EBUFS) {
 			if ((recvd = gitno_recv(buf)) < 0)
@@ -209,12 +209,13 @@ static int fetch_setup_walk(git_revwalk **out, git_repository *repo)
 	git_strarray refs;
 	unsigned int i;
 	git_reference *ref;
+	int error;
 
-	if (git_reference_list(&refs, repo) < 0)
-		return -1;
+	if ((error = git_reference_list(&refs, repo)) < 0)
+		return error;
 
-	if (git_revwalk_new(&walk, repo) < 0)
-		return -1;
+	if ((error = git_revwalk_new(&walk, repo)) < 0)
+		return error;
 
 	git_revwalk_sorting(walk, GIT_SORT_TIME);
 
@@ -223,13 +224,13 @@ static int fetch_setup_walk(git_revwalk **out, git_repository *repo)
 		if (!git__prefixcmp(refs.strings[i], GIT_REFS_TAGS_DIR))
 			continue;
 
-		if (git_reference_lookup(&ref, repo, refs.strings[i]) < 0)
+		if ((error = git_reference_lookup(&ref, repo, refs.strings[i])) < 0)
 			goto on_error;
 
 		if (git_reference_type(ref) == GIT_REF_SYMBOLIC)
 			continue;
 
-		if (git_revwalk_push(walk, git_reference_target(ref)) < 0)
+		if ((error = git_revwalk_push(walk, git_reference_target(ref))) < 0)
 			goto on_error;
 
 		git_reference_free(ref);
@@ -242,7 +243,7 @@ static int fetch_setup_walk(git_revwalk **out, git_repository *repo)
 on_error:
 	git_reference_free(ref);
 	git_strarray_free(&refs);
-	return -1;
+	return error;
 }
 
 static int wait_while_ack(gitno_buffer *buf)
@@ -503,7 +504,7 @@ int git_smart__download_pack(
 	}
 
 	if ((error = git_repository_odb__weakptr(&odb, repo)) < 0 ||
-		((error = git_odb_write_pack(&writepack, odb, progress_cb, progress_payload)) < 0))
+		((error = git_odb_write_pack(&writepack, odb, progress_cb, progress_payload)) != 0))
 		goto done;
 
 	/*
@@ -539,11 +540,9 @@ int git_smart__download_pack(
 		if (pkt->type == GIT_PKT_PROGRESS) {
 			if (t->progress_cb) {
 				git_pkt_progress *p = (git_pkt_progress *) pkt;
-				if (t->progress_cb(p->data, p->len, t->message_cb_payload)) {
-					giterr_clear();
-					error = GIT_EUSER;
+				error = t->progress_cb(p->data, p->len, t->message_cb_payload);
+				if (error)
 					goto done;
-				}
 			}
 			git__free(pkt);
 		} else if (pkt->type == GIT_PKT_DATA) {
@@ -551,7 +550,7 @@ int git_smart__download_pack(
 			error = writepack->append(writepack, p->data, p->len, stats);
 
 			git__free(pkt);
-			if (error < 0)
+			if (error != 0)
 				goto done;
 		} else if (pkt->type == GIT_PKT_FLUSH) {
 			/* A flush indicates the end of the packfile */
@@ -564,17 +563,15 @@ int git_smart__download_pack(
 	 * Trailing execution of progress_cb, if necessary...
 	 * Only the callback through the npp datastructure currently
 	 * updates the last_fired_bytes value. It is possible that
-	 * progress has already been reported with the correct 
+	 * progress has already been reported with the correct
 	 * "received_bytes" value, but until (if?) this is unified
 	 * then we will report progress again to be sure that the
 	 * correct last received_bytes value is reported.
 	 */
 	if (npp.callback && npp.stats->received_bytes > npp.last_fired_bytes) {
-		if (npp.callback(npp.stats, npp.payload) < 0) {
-			giterr_clear();
-			error = GIT_EUSER;
+		error = npp.callback(npp.stats, npp.payload);
+		if (error != 0)
 			goto done;
-		}
 	}
 
 	error = writepack->commit(writepack, stats);
diff --git a/src/transports/winhttp.c b/src/transports/winhttp.c
index 673cd0faf..e47e19cca 100644
--- a/src/transports/winhttp.c
+++ b/src/transports/winhttp.c
@@ -667,9 +667,11 @@ replay:
 			if (allowed_types &&
 				(!t->cred || 0 == (t->cred->credtype & allowed_types))) {
 
-				if (t->owner->cred_acquire_cb(&t->cred, t->owner->url, t->connection_data.user, allowed_types, 
-					t->owner->cred_acquire_payload) < 0)
-					return GIT_EUSER;
+				int error = t->owner->cred_acquire_cb(
+					&t->cred, t->owner->url, t->connection_data.user,
+					allowed_types, t->owner->cred_acquire_payload);
+				if (error < 0)
+					return error;
 
 				assert(t->cred);
 
diff --git a/src/tree.c b/src/tree.c
index 8ded007eb..5f35ac3a8 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -883,9 +883,8 @@ static int tree_walk(
 
 	git_vector_foreach(&tree->entries, i, entry) {
 		if (preorder) {
-			error = callback(path->ptr, entry, payload);
-			if (error < 0)
-				return giterr_user_cancel();
+			if ((error = callback(path->ptr, entry, payload)) < 0)
+				return giterr_set_callback(error, "git_tree_walk");
 			if (error > 0) {
 				error = 0;
 				continue;
@@ -896,8 +895,8 @@ static int tree_walk(
 			git_tree *subtree;
 			size_t path_len = git_buf_len(path);
 
-			if ((error = git_tree_lookup(
-				&subtree, tree->object.repo, &entry->oid)) < 0)
+			error = git_tree_lookup(&subtree, tree->object.repo, &entry->oid);
+			if (error < 0)
 				break;
 
 			/* append the next entry to the path */
@@ -905,19 +904,22 @@ static int tree_walk(
 			git_buf_putc(path, '/');
 
 			if (git_buf_oom(path))
-				return -1;
+				error = -1;
+			else
+				error = tree_walk(subtree, callback, path, payload, preorder);
 
-			error = tree_walk(subtree, callback, path, payload, preorder);
 			git_tree_free(subtree);
-
 			if (error != 0)
 				break;
 
 			git_buf_truncate(path, path_len);
 		}
 
-		if (!preorder && callback(path->ptr, entry, payload) < 0)
-			return giterr_user_cancel();
+		if (!preorder) {
+			if ((error = callback(path->ptr, entry, payload)) < 0)
+				return giterr_set_callback(error, "git_tree_walk");
+			error = 0;
+		}
 	}
 
 	return error;
diff --git a/src/vector.c b/src/vector.c
index 9e217b831..b1ea89606 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -104,6 +104,22 @@ int git_vector_init(git_vector *v, size_t initial_size, git_vector_cmp cmp)
 	return resize_vector(v, max(initial_size, MIN_ALLOCSIZE));
 }
 
+void **git_vector_detach(size_t *size, size_t *asize, git_vector *v)
+{
+	void **data = v->contents;
+
+	if (size)
+		*size = v->length;
+	if (asize)
+		*asize = v->_alloc_size;
+
+	v->_alloc_size = 0;
+	v->length   = 0;
+	v->contents = NULL;
+
+	return data;
+}
+
 int git_vector_insert(git_vector *v, void *element)
 {
 	assert(v);
diff --git a/src/vector.h b/src/vector.h
index c6d3e9d55..defe22466 100644
--- a/src/vector.h
+++ b/src/vector.h
@@ -28,6 +28,8 @@ void git_vector_clear(git_vector *v);
 int git_vector_dup(git_vector *v, const git_vector *src, git_vector_cmp cmp);
 void git_vector_swap(git_vector *a, git_vector *b);
 
+void **git_vector_detach(size_t *size, size_t *asize, git_vector *v);
+
 void git_vector_sort(git_vector *v);
 
 /** Linear search for matching entry using internal comparison function */
diff --git a/tests/attr/repo.c b/tests/attr/repo.c
index ef2ad5ce9..f9ba585fb 100644
--- a/tests/attr/repo.c
+++ b/tests/attr/repo.c
@@ -129,6 +129,8 @@ static int count_attrs(
 	return 0;
 }
 
+#define CANCEL_VALUE 12345
+
 static int cancel_iteration(
 	const char *name,
 	const char *value,
@@ -140,7 +142,7 @@ static int cancel_iteration(
 	*((int *)payload) -= 1;
 
 	if (*((int *)payload) < 0)
-		return -1;
+		return CANCEL_VALUE;
 
 	return 0;
 }
@@ -166,7 +168,7 @@ void test_attr_repo__foreach(void)
 
 	count = 2;
 	cl_assert_equal_i(
-		GIT_EUSER, git_attr_foreach(
+		CANCEL_VALUE, git_attr_foreach(
 			g_repo, 0, "sub/subdir_test1", &cancel_iteration, &count)
 	);
 }
diff --git a/tests/config/read.c b/tests/config/read.c
index abc088d59..25672729f 100644
--- a/tests/config/read.c
+++ b/tests/config/read.c
@@ -247,7 +247,7 @@ void test_config_read__foreach(void)
 
 	count = 3;
 	cl_git_fail(ret = git_config_foreach(cfg, cfg_callback_countdown, &count));
-	cl_assert_equal_i(GIT_EUSER, ret);
+	cl_assert_equal_i(-100, ret);
 
 	git_config_free(cfg);
 }
diff --git a/tests/config/rename.c b/tests/config/rename.c
index 29ade7b00..db07c798f 100644
--- a/tests/config/rename.c
+++ b/tests/config/rename.c
@@ -44,7 +44,6 @@ void test_config_rename__can_rename(void)
 void test_config_rename__prevent_overwrite(void)
 {
 	const git_config_entry *ce;
-	const git_error *err;
 
 	cl_git_pass(git_config_set_string(
 		g_config, "branch.local-track.remote", "yellow"));
@@ -60,8 +59,12 @@ void test_config_rename__prevent_overwrite(void)
 		&ce, g_config, "branch.local-track.remote"));
 	cl_assert_equal_s(".", ce->value);
 
-//	cl_assert((err = giterr_last()) != NULL);
-//	cl_assert(err->message != NULL);
+	/* so, we don't currently prevent overwrite... */
+	/* {
+		const git_error *err;
+		cl_assert((err = giterr_last()) != NULL);
+		cl_assert(err->message != NULL);
+	} */
 }
 
 static void assert_invalid_config_section_name(
diff --git a/tests/core/path.c b/tests/core/path.c
index 3858e30dd..471491b87 100644
--- a/tests/core/path.c
+++ b/tests/core/path.c
@@ -354,13 +354,15 @@ typedef struct {
 	char **expect;
 } check_walkup_info;
 
+#define CANCEL_VALUE 1234
+
 static int check_one_walkup_step(void *ref, git_buf *path)
 {
 	check_walkup_info *info = (check_walkup_info *)ref;
 
 	if (!info->cancel_after) {
 		cl_assert_equal_s(info->expect[info->expect_idx], "[CANCEL]");
-		return -1;
+		return CANCEL_VALUE;
 	}
 	info->cancel_after--;
 
@@ -435,7 +437,7 @@ void test_core_path__11a_walkup_cancel(void)
 		info.expect_idx = i;
 
 		cl_assert_equal_i(
-			GIT_EUSER,
+			CANCEL_VALUE,
 			git_path_walk_up(&p, root[j], check_one_walkup_step, &info)
 		);
 
diff --git a/tests/diff/index.c b/tests/diff/index.c
index 8f4567137..21afe8da2 100644
--- a/tests/diff/index.c
+++ b/tests/diff/index.c
@@ -128,9 +128,7 @@ void test_diff_index__1(void)
 	cl_git_pass(git_diff_tree_to_index(&diff, g_repo, a, NULL, &opts));
 
 	cl_assert_equal_i(
-		GIT_EUSER,
-		git_diff_foreach(diff, diff_stop_after_2_files, NULL, NULL, &exp)
-	);
+		1, git_diff_foreach(diff, diff_stop_after_2_files, NULL, NULL, &exp) );
 
 	cl_assert_equal_i(2, exp.files);
 
diff --git a/tests/diff/notify.c b/tests/diff/notify.c
index cc33cb71c..f6accd004 100644
--- a/tests/diff/notify.c
+++ b/tests/diff/notify.c
@@ -20,7 +20,7 @@ static int assert_called_notifications(
 {
 	bool found = false;
 	notify_expected *exp = (notify_expected*)payload;
-	notify_expected *e;;
+	notify_expected *e;
 
 	GIT_UNUSED(diff_so_far);
 
diff --git a/tests/diff/rename.c b/tests/diff/rename.c
index ca6d076d6..93e69f479 100644
--- a/tests/diff/rename.c
+++ b/tests/diff/rename.c
@@ -111,6 +111,28 @@ void test_diff_rename__match_oid(void)
 
 	git_diff_free(diff);
 
+	cl_git_pass(git_diff_tree_to_tree(
+		&diff, g_repo, old_tree, new_tree, &diffopts));
+
+	/* git diff --find-copies-harder -M100 -B100 \
+	 *          31e47d8c1fa36d7f8d537b96158e3f024de0a9f2 \
+	 *          2bc7f351d20b53f1c72c16c4b036e491c478c49a
+	 */
+	opts.flags = GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED |
+		GIT_DIFF_FIND_EXACT_MATCH_ONLY;
+	cl_git_pass(git_diff_find_similar(diff, &opts));
+
+	memset(&exp, 0, sizeof(exp));
+	cl_git_pass(git_diff_foreach(
+		diff, diff_file_cb, diff_hunk_cb, diff_line_cb, &exp));
+
+	cl_assert_equal_i(3, exp.files);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_UNMODIFIED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_COPIED]);
+	cl_assert_equal_i(1, exp.file_status[GIT_DELTA_RENAMED]);
+
+	git_diff_free(diff);
+
 	git_tree_free(old_tree);
 	git_tree_free(new_tree);
 }
diff --git a/tests/notes/notes.c b/tests/notes/notes.c
index 82dcaf8ca..c2579a2c4 100644
--- a/tests/notes/notes.c
+++ b/tests/notes/notes.c
@@ -129,7 +129,7 @@ void test_notes_notes__can_cancel_foreach(void)
 	create_note(&note_oid4, "refs/notes/i-can-see-dead-notes", "4a202b346bb0fb0db7eff3cffeb3c70babbd2045", "I decorate 9fd7 and 4a20\n");
 
 	cl_assert_equal_i(
-		GIT_EUSER,
+		1,
 		git_note_foreach(_repo, "refs/notes/i-can-see-dead-notes",
 			note_cancel_cb, &retrieved_notes));
 }
diff --git a/tests/object/tree/walk.c b/tests/object/tree/walk.c
index 1207e864c..f8005e579 100644
--- a/tests/object/tree/walk.c
+++ b/tests/object/tree/walk.c
@@ -59,7 +59,7 @@ static int treewalk_stop_cb(
 
 	(*count) += 1;
 
-	return (*count == 2) ? -1 : 0;
+	return (*count == 2) ? -123 : 0;
 }
 
 static int treewalk_stop_immediately_cb(
@@ -83,20 +83,20 @@ void test_object_tree_walk__1(void)
 
 	ct = 0;
 	cl_assert_equal_i(
-		GIT_EUSER, git_tree_walk(tree, GIT_TREEWALK_PRE, treewalk_stop_cb, &ct));
+		-123, git_tree_walk(tree, GIT_TREEWALK_PRE, treewalk_stop_cb, &ct));
 	cl_assert_equal_i(2, ct);
 
 	ct = 0;
 	cl_assert_equal_i(
-		GIT_EUSER, git_tree_walk(tree, GIT_TREEWALK_POST, treewalk_stop_cb, &ct));
+		-123, git_tree_walk(tree, GIT_TREEWALK_POST, treewalk_stop_cb, &ct));
 	cl_assert_equal_i(2, ct);
 
 	cl_assert_equal_i(
-		GIT_EUSER, git_tree_walk(
+		-100, git_tree_walk(
 			tree, GIT_TREEWALK_PRE, treewalk_stop_immediately_cb, NULL));
 
 	cl_assert_equal_i(
-		GIT_EUSER, git_tree_walk(
+		-100, git_tree_walk(
 			tree, GIT_TREEWALK_POST, treewalk_stop_immediately_cb, NULL));
 
 	git_tree_free(tree);
@@ -152,7 +152,7 @@ void test_object_tree_walk__2(void)
 	memset(&data, 0, sizeof(data));
 	data.stop = "3.txt";
 
-	cl_assert_equal_i(GIT_EUSER, git_tree_walk(
+	cl_assert_equal_i(-1, git_tree_walk(
 		tree, GIT_TREEWALK_PRE, treewalk_skip_de_cb, &data));
 	cl_assert_equal_i(3, data.files);
 	cl_assert_equal_i(2, data.dirs);
@@ -168,7 +168,7 @@ void test_object_tree_walk__2(void)
 	memset(&data, 0, sizeof(data));
 	data.stop = "new.txt";
 
-	cl_assert_equal_i(GIT_EUSER, git_tree_walk(
+	cl_assert_equal_i(-1, git_tree_walk(
 		tree, GIT_TREEWALK_PRE, treewalk_skip_de_cb, &data));
 	cl_assert_equal_i(7, data.files);
 	cl_assert_equal_i(4, data.dirs);
diff --git a/tests/odb/foreach.c b/tests/odb/foreach.c
index ebb8866f7..256ae9cd7 100644
--- a/tests/odb/foreach.c
+++ b/tests/odb/foreach.c
@@ -5,7 +5,6 @@
 
 static git_odb *_odb;
 static git_repository *_repo;
-static int nobj;
 
 void test_odb_foreach__cleanup(void)
 {
@@ -18,10 +17,10 @@ void test_odb_foreach__cleanup(void)
 
 static int foreach_cb(const git_oid *oid, void *data)
 {
-	GIT_UNUSED(data);
-	GIT_UNUSED(oid);
+	int *nobj = data;
+	(*nobj)++;
 
-	nobj++;
+	GIT_UNUSED(oid);
 
 	return 0;
 }
@@ -38,43 +37,46 @@ static int foreach_cb(const git_oid *oid, void *data)
  */
 void test_odb_foreach__foreach(void)
 {
+	int nobj = 0;
+
 	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
 	git_repository_odb(&_odb, _repo);
 
-	cl_git_pass(git_odb_foreach(_odb, foreach_cb, NULL));
+	cl_git_pass(git_odb_foreach(_odb, foreach_cb, &nobj));
 	cl_assert_equal_i(47 + 1640, nobj); /* count + in-pack */
 }
 
 void test_odb_foreach__one_pack(void)
 {
 	git_odb_backend *backend = NULL;
+	int nobj = 0;
 
 	cl_git_pass(git_odb_new(&_odb));
 	cl_git_pass(git_odb_backend_one_pack(&backend, cl_fixture("testrepo.git/objects/pack/pack-a81e489679b7d3418f9ab594bda8ceb37dd4c695.idx")));
 	cl_git_pass(git_odb_add_backend(_odb, backend, 1));
 	_repo = NULL;
 
-	nobj = 0;
-	cl_git_pass(git_odb_foreach(_odb, foreach_cb, NULL));
+	cl_git_pass(git_odb_foreach(_odb, foreach_cb, &nobj));
 	cl_assert(nobj == 1628);
 }
 
 static int foreach_stop_cb(const git_oid *oid, void *data)
 {
-	GIT_UNUSED(data);
-	GIT_UNUSED(oid);
+	int *nobj = data;
+	(*nobj)++;
 
-	nobj++;
+	GIT_UNUSED(oid);
 
-	return (nobj == 1000);
+	return (*nobj == 1000) ? -321 : 0;
 }
 
 void test_odb_foreach__interrupt_foreach(void)
 {
-	nobj = 0;
+	int nobj = 0;
+
 	cl_git_pass(git_repository_open(&_repo, cl_fixture("testrepo.git")));
 	git_repository_odb(&_odb, _repo);
 
-	cl_assert_equal_i(GIT_EUSER, git_odb_foreach(_odb, foreach_stop_cb, NULL));
+	cl_assert_equal_i(-321, git_odb_foreach(_odb, foreach_stop_cb, &nobj));
 	cl_assert(nobj == 1000);
 }
diff --git a/tests/online/clone.c b/tests/online/clone.c
index efc76d958..be4421ae5 100644
--- a/tests/online/clone.c
+++ b/tests/online/clone.c
@@ -273,7 +273,7 @@ static int cancel_at_half(const git_transfer_progress *stats, void *payload)
 	GIT_UNUSED(payload);
 
 	if (stats->received_objects > (stats->total_objects/2))
-		return 1;
+		return 4321;
 	return 0;
 }
 
@@ -281,7 +281,8 @@ void test_online_clone__can_cancel(void)
 {
 	g_options.remote_callbacks.transfer_progress = cancel_at_half;
 
-	cl_git_fail_with(git_clone(&g_repo, LIVE_REPO_URL, "./foo", &g_options), GIT_EUSER);
+	cl_git_fail_with(
+		git_clone(&g_repo, LIVE_REPO_URL, "./foo", &g_options), 4321);
 }
 
 
diff --git a/tests/online/fetch.c b/tests/online/fetch.c
index 5153a7ae0..7e9dfdbbe 100644
--- a/tests/online/fetch.c
+++ b/tests/online/fetch.c
@@ -129,7 +129,7 @@ static int cancel_at_half(const git_transfer_progress *stats, void *payload)
 	GIT_UNUSED(payload);
 
 	if (stats->received_objects > (stats->total_objects/2))
-		return -1;
+		return -4321;
 	return 0;
 }
 
@@ -147,7 +147,7 @@ void test_online_fetch__can_cancel(void)
 	git_remote_set_callbacks(remote, &callbacks);
 
 	cl_git_pass(git_remote_connect(remote, GIT_DIRECTION_FETCH));
-	cl_git_fail_with(git_remote_download(remote), GIT_EUSER);
+	cl_git_fail_with(git_remote_download(remote), -4321);
 	git_remote_disconnect(remote);
 	git_remote_free(remote);
 }
diff --git a/tests/refs/foreachglob.c b/tests/refs/foreachglob.c
index 2c458082f..c0f6ce763 100644
--- a/tests/refs/foreachglob.c
+++ b/tests/refs/foreachglob.c
@@ -81,14 +81,14 @@ static int interrupt_cb(const char *reference_name, void *payload)
 
 	(*count)++;
 
-	return (*count == 11);
+	return (*count == 11) ? -1000 : 0;
 }
 
 void test_refs_foreachglob__can_cancel(void)
 {
 	int count = 0;
 
-	cl_assert_equal_i(GIT_EUSER, git_reference_foreach_glob(
+	cl_assert_equal_i(-1000, git_reference_foreach_glob(
 		repo, "*", interrupt_cb, &count) );
 
 	cl_assert_equal_i(11, count);
diff --git a/tests/status/worktree.c b/tests/status/worktree.c
index 34be6d34c..fd57fcc1e 100644
--- a/tests/status/worktree.c
+++ b/tests/status/worktree.c
@@ -552,7 +552,7 @@ static int cb_status__interrupt(const char *p, unsigned int s, void *payload)
 
 	(*count)++;
 
-	return (*count == 8);
+	return (*count == 8) ? -111 : 0;
 }
 
 void test_status_worktree__interruptable_foreach(void)
@@ -561,7 +561,7 @@ void test_status_worktree__interruptable_foreach(void)
 	git_repository *repo = cl_git_sandbox_init("status");
 
 	cl_assert_equal_i(
-		GIT_EUSER, git_status_foreach(repo, cb_status__interrupt, &count)
+		-111, git_status_foreach(repo, cb_status__interrupt, &count)
 	);
 
 	cl_assert_equal_i(8, count);