Update behavior for postCommand.strategy=post-index-change

Documentation/config/postcommand.adoc

@@ -7,7 +7,7 @@ postCommand.strategy::
 `always`;;
 	run the `post-command` hook on every process (default).
 
-`post-index-change`;;
+`worktree-change`;;
 	run the `post-command` hook only if the current process wrote to
-	the index.
+	the index and updated the worktree.
 ----

hook.c

@@ -190,7 +190,11 @@ static char *get_post_index_change_sentinel_name(struct repository *r)
 	if (slash)
 		*slash = 0;
 
-	repo_git_path_replace(r, &path, "hooks/index-change-%s.snt", sid);
+	/*
+	 * Do not write to hooks directory, as it could be redirected
+	 * somewhere like the source tree.
+	 */
+	repo_git_path_replace(r, &path, "info/index-change-%s.snt", sid);
 
 	return strbuf_detach(&path, NULL);
 }
@@ -229,6 +233,37 @@ static int post_index_change_sentinel_exists(struct repository *r)
 	return res;
 }
 
+/**
+ * See if we can replace the requested hook with an internal behavior.
+ * Returns 0 if the real hook should run. Returns nonzero if we instead
+ * executed custom internal behavior and the real hook should not run.
+ */
+static int handle_hook_replacement(struct repository *r,
+				   const char *hook_name,
+				   struct strvec *args)
+{
+	const char *strval;
+	if (repo_config_get_string_tmp(r, "postcommand.strategy", &strval) ||
+	    strcasecmp(strval, "worktree-change"))
+		return 0;
+
+	if (!strcmp(hook_name, "post-index-change")) {
+		/* Create a sentinel file only if the worktree changed. */
+		if (!strcmp(args->v[0], "1"))
+			write_post_index_change_sentinel(r);
+
+		/* We don't skip post-index-change hooks that exist. */
+		return 0;
+	}
+	if (!strcmp(hook_name, "post-command") &&
+	    !post_index_change_sentinel_exists(r)) {
+		/* We skip the post-command hook in this case. */
+		return 1;
+	}
+
+	return 0;
+}
+
 int run_hooks_opt(struct repository *r, const char *hook_name,
 		  struct run_hooks_opt *options)
 {
@@ -255,17 +290,9 @@ int run_hooks_opt(struct repository *r, const char *hook_name,
 	};
 
 	/* Interject hook behavior depending on strategy. */
-	if (r && r->gitdir) {
-		const char *strval;
-		if (!repo_config_get_string_tmp(r, "postcommand.strategy", &strval) &&
-		    !strcasecmp(strval, "post-index-change")) {
-			if (!strcmp(hook_name, "post-index-change"))
-				return write_post_index_change_sentinel(r);
-			if (!strcmp(hook_name, "post-command") &&
-			    !post_index_change_sentinel_exists(r))
-				return 0;
-		}
-	}
+	if (r && r->gitdir &&
+	    handle_hook_replacement(r, hook_name, &options->args))
+		return 0;
 
 	hook_path = find_hook(r, hook_name);
 

t/t0401-post-command-hook.sh

@@ -32,14 +32,20 @@ test_expect_success 'with failing pre-command hook' '
 '
 
 test_expect_success 'with post-index-change config' '
-	mkdir -p .git/hooks &&
-	write_script .git/hooks/post-command <<-EOF &&
+	mkdir -p internal-hooks &&
+	write_script internal-hooks/post-command <<-EOF &&
 	echo ran >post-command.out
 	EOF
-	write_script .git/hooks/post-index-change <<-EOF &&
+	write_script internal-hooks/post-index-change <<-EOF &&
 	echo ran >post-index-change.out
 	EOF
 
+	# prevent writing of sentinel files to this directory.
+	test_when_finished chmod 775 internal-hooks &&
+	chmod a-w internal-hooks &&
+
+	git config core.hooksPath internal-hooks &&
+
 	# First, show expected behavior.
 	echo ran >expect &&
 	rm -f post-command.out post-index-change.out &&
@@ -57,18 +63,26 @@ test_expect_success 'with post-index-change config' '
 	test_cmp expect post-command.out &&
 
 	# Now, show configured behavior
-	git config postCommand.strategy post-index-change &&
-	rm -f post-command.out post-index-change.out &&
+	git config postCommand.strategy worktree-change &&
 
 	# rev-parse leaves index intact and thus skips post-command.
+	rm -f post-command.out post-index-change.out &&
 	git rev-parse HEAD &&
 	test_path_is_missing post-index-change.out &&
 	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.
+	rm -f post-command.out post-index-change.out &&
 	git add file &&
-	test_path_is_missing post-index-change.out &&
+	test_cmp expect post-index-change.out &&
+	test_path_is_missing post-command.out &&
+
+	echo stuff >>file &&
+	# reset --hard updates the worktree.
+	rm -f post-command.out post-index-change.out &&
+	git reset --hard &&
+	test_cmp expect post-index-change.out &&
 	test_cmp expect post-command.out
 '