hook: restrict post-command hook even more

The postCommand.strategy=post-index-change config was designed to
replace some internal hook usage. This internal hook was more
restrictive than the initial feature was designed. Specifically, it
ignored index updates that did not update the worktree. With the
existing implementation, this causes more work done in the post-command
hook than intended.

Update the code to write a sentinel file only when the worktree is
changed.

Signed-off-by: Derrick Stolee <stolee@gmail.com>

Author: derrickstolee

Documentation/config/postcommand.adoc

@@ -9,5 +9,5 @@ postCommand.strategy::
 
 `post-index-change`;;
 	run the `post-command` hook only if the current process wrote to
-	the index.
+	the index and updated the worktree.
 ----

hook.c

@@ -241,6 +241,7 @@ static int post_index_change_sentinel_exists(struct repository *r)
  */
 static int handle_hook_replacement(struct repository *r,
 				   const char *hook_name,
+				   struct strvec *args,
 				   int *result)
 {
 	const char *strval;
@@ -249,7 +250,11 @@ static int handle_hook_replacement(struct repository *r,
 		return 0;
 
 	if (!strcmp(hook_name, "post-index-change")) {
-		*result = write_post_index_change_sentinel(r);
+		/* Create a sentinel file only if the worktree changed. */
+		if (!strcmp(args->v[0], "1"))
+			*result = write_post_index_change_sentinel(r);
+		else
+			*result = 0;
 		return 1;
 	}
 	if (!strcmp(hook_name, "post-command") &&
@@ -289,7 +294,8 @@ int run_hooks_opt(struct repository *r, const char *hook_name,
 	/* Interject hook behavior depending on strategy. */
 	if (r && r->gitdir) {
 		int result = 0;
-		if (handle_hook_replacement(r, hook_name, &result))
+		if (handle_hook_replacement(r, hook_name,
+					    &options->args, &result))
 			return result;
 	}
 

t/t0401-post-command-hook.sh

@@ -72,9 +72,15 @@ test_expect_success 'with post-index-change config' '
 	test_path_is_missing post-command.out &&
 
 	echo stuff >>file &&
-	# add updates the index and runs post-command.
+	# add keeps the worktree the same, so does not run post-command.
 	git add file &&
 	test_path_is_missing post-index-change.out &&
+	test_path_is_missing post-command.out &&
+
+	echo stuff >>file &&
+	# reset --hard updates the worktree.
+	git reset --hard &&
+	test_path_is_missing post-index-change.out &&
 	test_cmp expect post-command.out
 '