Merge branch 'jc/push-to-checkout'

Extending the js/push-to-deploy topic, the behaviour of "git push"
when updating the working tree and the index with an update to the
branch that is checked out can be tweaked by push-to-checkout hook.

* jc/push-to-checkout:
  receive-pack: support push-to-checkout hook
  receive-pack: refactor updateInstead codepath

4 files changed, 143 insertions, 26 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 1a54eae8f8..ae6791db12 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2158,11 +2158,15 @@ receive.denyCurrentBranch::
 	message. Defaults to "refuse".
 +
 Another option is "updateInstead" which will update the working
-directory (must be clean) if pushing into the current branch. This option is
+tree if pushing into the current branch.  This option is
 intended for synchronizing working directories when one side is not easily
 accessible via interactive ssh (e.g. a live web site, hence the requirement
 that the working directory be clean). This mode also comes in handy when
 developing inside a VM to test and fix code on different Operating Systems.
++
+By default, "updateInstead" will refuse the push if the working tree or
+the index have any difference from the HEAD, but the `push-to-checkout`
+hook can be used to customize this.  See linkgit:githooks[5].
 
 receive.denyNonFastForwards::
 	If set to true, git-receive-pack will deny a ref update which is
diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 9ef2469373..7ba0ac965d 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -341,6 +341,36 @@ Both standard output and standard error output are forwarded to
 'git send-pack' on the other end, so you can simply `echo` messages
 for the user.
 
+push-to-checkout
+~~~~~~~~~~~~~~~~
+
+This hook is invoked by 'git-receive-pack' on the remote repository,
+which happens when a 'git push' is done on a local repository, when
+the push tries to update the branch that is currently checked out
+and the `receive.denyCurrentBranch` configuration variable is set to
+`updateInstead`.  Such a push by default is refused if the working
+tree and the index of the remote repository has any difference from
+the currently checked out commit; when both the working tree and the
+index match the current commit, they are updated to match the newly
+pushed tip of the branch.  This hook is to be used to override the
+default behaviour.
+
+The hook receives the commit with which the tip of the current
+branch is going to be updated.  It can exit with a non-zero status
+to refuse the push (when it does so, it must not modify the index or
+the working tree).  Or it can make any necessary changes to the
+working tree and to the index to bring them to the desired state
+when the tip of the current branch is updated to the new commit, and
+exit with a zero status.
+
+For example, the hook can simply run `git read-tree -u -m HEAD "$1"`
+in order to emulate 'git fetch' that is run in the reverse direction
+with `git push`, as the two-tree form of `read-tree -u -m` is
+essentially the same as `git checkout` that switches branches while
+keeping the local changes in the working tree that do not interfere
+with the difference between the branches.
+
+
 pre-auto-gc
 ~~~~~~~~~~~
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 4e85e25d0f..e0ce78e5a0 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -743,7 +743,9 @@ static int update_shallow_ref(struct command *cmd, struct shallow_info *si)
 	return 0;
 }
 
-static const char *update_worktree(unsigned char *sha1)
+static const char *push_to_deploy(unsigned char *sha1,
+				  struct argv_array *env,
+				  const char *work_tree)
 {
 	const char *update_refresh[] = {
 		"update-index", "-q", "--ignore-submodules", "--refresh", NULL
@@ -758,69 +760,87 @@ static const char *update_worktree(unsigned char *sha1)
 	const char *read_tree[] = {
 		"read-tree", "-u", "-m", NULL, NULL
 	};
-	const char *work_tree = git_work_tree_cfg ? git_work_tree_cfg : "..";
-	struct argv_array env = ARGV_ARRAY_INIT;
 	struct child_process child = CHILD_PROCESS_INIT;
 
-	if (is_bare_repository())
-		return "denyCurrentBranch = updateInstead needs a worktree";
-
-	argv_array_pushf(&env, "GIT_DIR=%s", absolute_path(get_git_dir()));
-
 	child.argv = update_refresh;
-	child.env = env.argv;
+	child.env = env->argv;
 	child.dir = work_tree;
 	child.no_stdin = 1;
 	child.stdout_to_stderr = 1;
 	child.git_cmd = 1;
-	if (run_command(&child)) {
-		argv_array_clear(&env);
+	if (run_command(&child))
 		return "Up-to-date check failed";
-	}
 
 	/* run_command() does not clean up completely; reinitialize */
 	child_process_init(&child);
 	child.argv = diff_files;
-	child.env = env.argv;
+	child.env = env->argv;
 	child.dir = work_tree;
 	child.no_stdin = 1;
 	child.stdout_to_stderr = 1;
 	child.git_cmd = 1;
-	if (run_command(&child)) {
-		argv_array_clear(&env);
+	if (run_command(&child))
 		return "Working directory has unstaged changes";
-	}
 
 	child_process_init(&child);
 	child.argv = diff_index;
-	child.env = env.argv;
+	child.env = env->argv;
 	child.no_stdin = 1;
 	child.no_stdout = 1;
 	child.stdout_to_stderr = 0;
 	child.git_cmd = 1;
-	if (run_command(&child)) {
-		argv_array_clear(&env);
+	if (run_command(&child))
 		return "Working directory has staged changes";
-	}
 
 	read_tree[3] = sha1_to_hex(sha1);
 	child_process_init(&child);
 	child.argv = read_tree;
-	child.env = env.argv;
+	child.env = env->argv;
 	child.dir = work_tree;
 	child.no_stdin = 1;
 	child.no_stdout = 1;
 	child.stdout_to_stderr = 0;
 	child.git_cmd = 1;
-	if (run_command(&child)) {
-		argv_array_clear(&env);
+	if (run_command(&child))
 		return "Could not update working tree to new HEAD";
-	}
 
-	argv_array_clear(&env);
 	return NULL;
 }
 
+static const char *push_to_checkout_hook = "push-to-checkout";
+
+static const char *push_to_checkout(unsigned char *sha1,
+				    struct argv_array *env,
+				    const char *work_tree)
+{
+	argv_array_pushf(env, "GIT_WORK_TREE=%s", absolute_path(work_tree));
+	if (run_hook_le(env->argv, push_to_checkout_hook,
+			sha1_to_hex(sha1), NULL))
+		return "push-to-checkout hook declined";
+	else
+		return NULL;
+}
+
+static const char *update_worktree(unsigned char *sha1)
+{
+	const char *retval;
+	const char *work_tree = git_work_tree_cfg ? git_work_tree_cfg : "..";
+	struct argv_array env = ARGV_ARRAY_INIT;
+
+	if (is_bare_repository())
+		return "denyCurrentBranch = updateInstead needs a worktree";
+
+	argv_array_pushf(&env, "GIT_DIR=%s", absolute_path(get_git_dir()));
+
+	if (!find_hook(push_to_checkout_hook))
+		retval = push_to_deploy(sha1, &env, work_tree);
+	else
+		retval = push_to_checkout(sha1, &env, work_tree);
+
+	argv_array_clear(&env);
+	return retval;
+}
+
 static const char *update(struct command *cmd, struct shallow_info *si)
 {
 	const char *name = cmd->ref_name;
diff --git a/t/t5516-fetch-push.sh b/t/t5516-fetch-push.sh
index 85c7fecd22..e4436c1700 100755
--- a/t/t5516-fetch-push.sh
+++ b/t/t5516-fetch-push.sh
@@ -1434,4 +1434,67 @@ test_expect_success 'receive.denyCurrentBranch = updateInstead' '
 
 '
 
+test_expect_success 'updateInstead with push-to-checkout hook' '
+	rm -fr testrepo &&
+	git init testrepo &&
+	(
+		cd testrepo &&
+		git pull .. master &&
+		git reset --hard HEAD^^ &&
+		git tag initial &&
+		git config receive.denyCurrentBranch updateInstead &&
+		write_script .git/hooks/push-to-checkout <<-\EOF
+		echo >&2 updating from $(git rev-parse HEAD)
+		echo >&2 updating to "$1"
+
+		git update-index -q --refresh &&
+		git read-tree -u -m HEAD "$1" || {
+			status=$?
+			echo >&2 read-tree failed
+			exit $status
+		}
+		EOF
+	) &&
+
+	# Try pushing into a pristine
+	git push testrepo master &&
+	(
+		cd testrepo &&
+		git diff --quiet &&
+		git diff HEAD --quiet &&
+		test $(git -C .. rev-parse HEAD) = $(git rev-parse HEAD)
+	) &&
+
+	# Try pushing into a repository with conflicting change
+	(
+		cd testrepo &&
+		git reset --hard initial &&
+		echo conflicting >path2
+	) &&
+	test_must_fail git push testrepo master &&
+	(
+		cd testrepo &&
+		test $(git rev-parse initial) = $(git rev-parse HEAD) &&
+		test conflicting = "$(cat path2)" &&
+		git diff-index --quiet --cached HEAD
+	) &&
+
+	# Try pushing into a repository with unrelated change
+	(
+		cd testrepo &&
+		git reset --hard initial &&
+		echo unrelated >path1 &&
+		echo irrelevant >path5 &&
+		git add path5
+	) &&
+	git push testrepo master &&
+	(
+		cd testrepo &&
+		test "$(cat path1)" = unrelated &&
+		test "$(cat path5)" = irrelevant &&
+		test "$(git diff --name-only --cached HEAD)" = path5 &&
+		test $(git -C .. rev-parse HEAD) = $(git rev-parse HEAD)
+	)
+'
+
 test_done