hooks: skip post-command hook more often (#813)

The postCommand.strategy=worktree-change config option allows for
skipping the post-command hook when the Git command doesn't change the
worktree. However, sometimes this config isn't loaded before the
post-command hook is invoked, causing the hook to run in cases where
we'd prefer it to not run.

Examples include: `git version` or `git <typo>`.

The tricky bit is that there are several places where we get here and
standard config mechanisms can't load due to not having a `gitdir` in
the repository struct. We fix this by:

1. Using the "load early config" mechanism also used by
`core.hooksPath`.
2. Skipping the lookup for the sentinel file when there isn't a `gitdir`
since we couldn't have written one without it.

The change is given in two commits: the first expands the tests with the
existing behavior and the second changes the behavior, showing the
impact on those tests.

* [X] This change only applies to microsoft/git specifics (post-command
hook)

See #736 and #748 for prior art in this space.

Author: derrickstolee

hook.c

@@ -219,9 +219,15 @@ static int write_post_index_change_sentinel(struct repository *r)
  */
 static int post_index_change_sentinel_exists(struct repository *r)
 {
-	char *path = get_post_index_change_sentinel_name(r);
+	char *path;
 	int res = 1;
 
+	/* It can't exist if we don't have a gitdir. */
+	if (!r->gitdir)
+		return 0;
+
+	path = get_post_index_change_sentinel_name(r);
+
 	if (unlink(path)) {
 		if (is_missing_file_error(errno))
 			res = 0;
@@ -233,6 +239,21 @@ static int post_index_change_sentinel_exists(struct repository *r)
 	return res;
 }
 
+static int check_worktree_change(const char *key, const char *value,
+				       UNUSED const struct config_context *ctx,
+				       void *data)
+{
+	int *enabled = data;
+
+	if (!strcmp(key, "postcommand.strategy") &&
+	    !strcasecmp(value, "worktree-change")) {
+		*enabled = 1;
+		return 1;
+	}
+
+	return 0;
+}
+
 /**
  * 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
@@ -242,9 +263,11 @@ 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"))
+	int enabled = 0;
+
+	read_early_config(r, check_worktree_change, &enabled);
+
+	if (!enabled)
 		return 0;
 
 	if (!strcmp(hook_name, "post-index-change")) {
@@ -290,8 +313,7 @@ int run_hooks_opt(struct repository *r, const char *hook_name,
 	};
 
 	/* Interject hook behavior depending on strategy. */
-	if (r && r->gitdir &&
-	    handle_hook_replacement(r, hook_name, &options->args))
+	if (r && handle_hook_replacement(r, hook_name, &options->args))
 		return 0;
 
 	hook_path = find_hook(r, hook_name);

t/t0401-post-command-hook.sh

@@ -78,12 +78,35 @@ test_expect_success 'with post-index-change config' '
 	test_cmp expect post-index-change.out &&
 	test_path_is_missing post-command.out &&
 
+	# add keeps the worktree the same, so does not run post-command.
+	# and this should work through an alias.
+	git config alias.addalias add &&
+	rm -f post-command.out post-index-change.out &&
+	echo more stuff >>file &&
+	git addalias file &&
+	test_cmp expect post-index-change.out &&
+	test_path_is_missing post-command.out &&
+
 	echo stuff >>file &&
 	# reset --hard updates the worktree.
+	# even through an alias
+	git config alias.resetalias "reset --hard" &&
 	rm -f post-command.out post-index-change.out &&
-	git reset --hard &&
+	git resetalias &&
 	test_cmp expect post-index-change.out &&
-	test_cmp expect post-command.out
+	test_cmp expect post-command.out &&
+
+	rm -f post-command.out &&
+	test_must_fail git && # get help text
+	test_path_is_missing post-command.out &&
+
+	rm -f post-command.out &&
+	git version &&
+	test_path_is_missing post-command.out &&
+
+	rm -f post-command.out &&
+	test_must_fail git typo &&
+	test_path_is_missing post-command.out
 '
 
 test_done