merge_file should use more aggressive levels

The default merge_file level was XDL_MERGE_MINIMAL, which will
produce conflicts where there should not be in the case where
both sides were changed identically.  Change the defaults to be
more aggressive (XDL_MERGE_ZEALOUS) which will more aggressively
compress non-conflicts.  This matches git.git's defaults.

Increase testing around reverting a previously reverted commit to
illustrate this problem.

4 files changed, 32 insertions, 13 deletions

diff --git a/src/checkout.c b/src/checkout.c
index e642c975e..cc49800a2 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -1626,6 +1626,7 @@ static int checkout_write_merge(
 {
 	git_buf our_label = GIT_BUF_INIT, their_label = GIT_BUF_INIT,
 		path_suffixed = GIT_BUF_INIT, path_workdir = GIT_BUF_INIT;
+	git_merge_file_options merge_file_opts = GIT_MERGE_FILE_OPTIONS_INIT;
 	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
 		ours = GIT_MERGE_FILE_INPUT_INIT,
 		theirs = GIT_MERGE_FILE_INPUT_INIT;
@@ -1662,7 +1663,7 @@ static int checkout_write_merge(
 		theirs.label = git_buf_cstr(&their_label);
 	}
 
-	if ((error = git_merge_files(&result, &ancestor, &ours, &theirs, 0)) < 0)
+	if ((error = git_merge_files(&result, &ancestor, &ours, &theirs, &merge_file_opts)) < 0)
 		goto done;
 
 	if (result.path == NULL || result.mode == 0) {
diff --git a/src/merge.c b/src/merge.c
index c0be37dd8..3ac9167e3 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -511,8 +511,9 @@ static int merge_conflict_resolve_automerge(
 	int *resolved,
 	git_merge_diff_list *diff_list,
 	const git_merge_diff *conflict,
-	unsigned int automerge_flags)
+	unsigned int merge_file_favor)
 {
+	git_merge_file_options merge_file_opts = GIT_MERGE_FILE_OPTIONS_INIT;
 	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
 		ours = GIT_MERGE_FILE_INPUT_INIT,
 		theirs = GIT_MERGE_FILE_INPUT_INIT;
@@ -526,9 +527,11 @@ static int merge_conflict_resolve_automerge(
 
 	*resolved = 0;
 
-	if (automerge_flags == GIT_MERGE_AUTOMERGE_NONE)
+	if (merge_file_favor == GIT_MERGE_FILE_FAVOR_NO_MERGE)
 		return 0;
 
+	merge_file_opts.favor = merge_file_favor;
+
 	/* Reject D/F conflicts */
 	if (conflict->type == GIT_MERGE_DIFF_DIRECTORY_FILE)
 		return 0;
@@ -552,7 +555,7 @@ static int merge_conflict_resolve_automerge(
 		(error = git_merge_file_input_from_index_entry(&ancestor, diff_list->repo, &conflict->ancestor_entry)) < 0 ||
 		(error = git_merge_file_input_from_index_entry(&ours, diff_list->repo, &conflict->our_entry)) < 0 ||
 		(error = git_merge_file_input_from_index_entry(&theirs, diff_list->repo, &conflict->their_entry)) < 0 ||
-		(error = git_merge_files(&result, &ancestor, &ours, &theirs, automerge_flags)) < 0 ||
+		(error = git_merge_files(&result, &ancestor, &ours, &theirs, &merge_file_opts)) < 0 ||
 		!result.automergeable ||
 		(error = git_odb_write(&automerge_oid, odb, result.data, result.len, GIT_OBJ_BLOB)) < 0)
 		goto done;
@@ -586,7 +589,7 @@ static int merge_conflict_resolve(
 	int *out,
 	git_merge_diff_list *diff_list,
 	const git_merge_diff *conflict,
-	unsigned int automerge_flags)
+	unsigned int merge_file_favor)
 {
 	int resolved = 0;
 	int error = 0;
@@ -596,14 +599,14 @@ static int merge_conflict_resolve(
 	if ((error = merge_conflict_resolve_trivial(&resolved, diff_list, conflict)) < 0)
 		goto done;
 
-	if (automerge_flags != GIT_MERGE_AUTOMERGE_NONE) {
+	if (merge_file_favor != GIT_MERGE_FILE_FAVOR_NO_MERGE) {
 		if (!resolved && (error = merge_conflict_resolve_one_removed(&resolved, diff_list, conflict)) < 0)
 			goto done;
 
 		if (!resolved && (error = merge_conflict_resolve_one_renamed(&resolved, diff_list, conflict)) < 0)
 			goto done;
 
-		if (!resolved && (error = merge_conflict_resolve_automerge(&resolved, diff_list, conflict, automerge_flags)) < 0)
+		if (!resolved && (error = merge_conflict_resolve_automerge(&resolved, diff_list, conflict, merge_file_favor)) < 0)
 			goto done;
 	}
 
@@ -1589,7 +1592,7 @@ int git_merge_trees(
 	git_vector_foreach(&changes, i, conflict) {
 		int resolved = 0;
 
-		if ((error = merge_conflict_resolve(&resolved, diff_list, conflict, opts.automerge_flags)) < 0)
+		if ((error = merge_conflict_resolve(&resolved, diff_list, conflict, opts.file_favor)) < 0)
 			goto done;
 
 		if (!resolved)
diff --git a/src/merge_file.c b/src/merge_file.c
index 48fc46e57..d13190276 100644
--- a/src/merge_file.c
+++ b/src/merge_file.c
@@ -130,7 +130,7 @@ int git_merge_files(
 	git_merge_file_input *ancestor,
 	git_merge_file_input *ours,
 	git_merge_file_input *theirs,
-	git_merge_automerge_flags flags)
+	git_merge_file_options *opts)
 {
 	xmparam_t xmparam;
 	mmbuffer_t mmbuffer;
@@ -152,12 +152,15 @@ int git_merge_files(
 	out->path = merge_file_best_path(ancestor, ours, theirs);
 	out->mode = merge_file_best_mode(ancestor, ours, theirs);
 
-	if (flags == GIT_MERGE_AUTOMERGE_FAVOR_OURS)
+	if (opts && opts->favor == GIT_MERGE_FILE_FAVOR_OURS)
 		xmparam.favor = XDL_MERGE_FAVOR_OURS;
-
-	if (flags == GIT_MERGE_AUTOMERGE_FAVOR_THEIRS)
+	else if (opts && opts->favor == GIT_MERGE_FILE_FAVOR_THEIRS)
 		xmparam.favor = XDL_MERGE_FAVOR_THEIRS;
 
+	xmparam.level = 
+		(opts && (opts->flags & GIT_MERGE_FILE_SIMPLIFY_ALNUM)) ?
+		XDL_MERGE_ZEALOUS_ALNUM : XDL_MERGE_ZEALOUS;
+
 	if ((xdl_result = xdl_merge(&ancestor->mmfile, &ours->mmfile,
 		&theirs->mmfile, &xmparam, &mmbuffer)) < 0) {
 		giterr_set(GITERR_MERGE, "Failed to merge files.");
diff --git a/src/merge_file.h b/src/merge_file.h
index 0af2f0a57..5d7ea9752 100644
--- a/src/merge_file.h
+++ b/src/merge_file.h
@@ -34,6 +34,18 @@ typedef struct {
 
 #define GIT_MERGE_FILE_RESULT_INIT	{0}
 
+typedef enum {
+	/* Condense non-alphanumeric regions for simplified diff file */
+	GIT_MERGE_FILE_SIMPLIFY_ALNUM = (1 << 0),
+} git_merge_file_flags_t;
+
+typedef struct {
+	git_merge_file_favor_t favor;
+	git_merge_file_flags_t flags;
+} git_merge_file_options;
+
+#define GIT_MERGE_FILE_OPTIONS_INIT	{0}
+
 int git_merge_file_input_from_index_entry(
 	git_merge_file_input *input,
 	git_repository *repo,
@@ -49,7 +61,7 @@ int git_merge_files(
 	git_merge_file_input *ancestor,
 	git_merge_file_input *ours,
 	git_merge_file_input *theirs,
-	git_merge_automerge_flags flags);
+	git_merge_file_options *opts);
 
 GIT_INLINE(void) git_merge_file_input_free(git_merge_file_input *input)
 {