worktree: report errors when unable to read locking reason

Git worktree's have the ability to be locked in order to spare them from
deletion, e.g. if a worktree is absent due to being located on a
removable disk it is a good idea to lock it. When locking such
worktrees, it is possible to give a locking reason in order to help the
user later on when inspecting status of any such locked trees.

The function `git_worktree_is_locked` serves to read out the locking
status. It currently does not properly report any errors when reading
the reason file, and callers are unexpecting of any negative return
values, too. Fix this by converting callers to expect error codes and
checking the return code of `git_futils_readbuffer`.

src/worktree.c

@@ -136,11 +136,11 @@ static int open_worktree_dir(git_worktree **out, const char *parent, const char
 		goto out;
 	}
 
-	if ((wt->name = git__strdup(name)) == NULL
-	    || (wt->commondir_path = git_worktree__read_link(dir, "commondir")) == NULL
-	    || (wt->gitlink_path = git_worktree__read_link(dir, "gitdir")) == NULL
-	    || (parent && (wt->parent_path = git__strdup(parent)) == NULL)
-	    || (wt->worktree_path = git_path_dirname(wt->gitlink_path)) == NULL) {
+	if ((wt->name = git__strdup(name)) == NULL ||
+	    (wt->commondir_path = git_worktree__read_link(dir, "commondir")) == NULL ||
+	    (wt->gitlink_path = git_worktree__read_link(dir, "gitdir")) == NULL ||
+	    (parent && (wt->parent_path = git__strdup(parent)) == NULL) ||
+	    (wt->worktree_path = git_path_dirname(wt->gitlink_path)) == NULL) {
 		error = -1;
 		goto out;
 	}
@@ -149,7 +149,10 @@ static int open_worktree_dir(git_worktree **out, const char *parent, const char
 		goto out;
 	wt->gitdir_path = git_buf_detach(&gitdir);
 
-	wt->locked = !!git_worktree_is_locked(NULL, wt);
+	if ((error = git_worktree_is_locked(NULL, wt)) < 0)
+		goto out;
+	wt->locked = !!error;
+	error = 0;
 
 	*out = wt;
 
@@ -403,20 +406,24 @@ out:
 int git_worktree_lock(git_worktree *wt, const char *reason)
 {
 	git_buf buf = GIT_BUF_INIT, path = GIT_BUF_INIT;
-	int err;
+	int error;
 
 	assert(wt);
 
-	if ((err = git_worktree_is_locked(NULL, wt)) < 0)
+	if ((error = git_worktree_is_locked(NULL, wt)) < 0)
+		goto out;
+	if (error) {
+		error = GIT_ELOCKED;
 		goto out;
+	}
 
-	if ((err = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
+	if ((error = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
 		goto out;
 
 	if (reason)
 		git_buf_attach_notowned(&buf, reason, strlen(reason));
 
-	if ((err = git_futils_writebuffer(&buf, path.ptr, O_CREAT|O_EXCL|O_WRONLY, 0644)) < 0)
+	if ((error = git_futils_writebuffer(&buf, path.ptr, O_CREAT|O_EXCL|O_WRONLY, 0644)) < 0)
 		goto out;
 
 	wt->locked = 1;
@@ -424,16 +431,19 @@ int git_worktree_lock(git_worktree *wt, const char *reason)
 out:
 	git_buf_dispose(&path);
 
-	return err;
+	return error;
 }
 
 int git_worktree_unlock(git_worktree *wt)
 {
 	git_buf path = GIT_BUF_INIT;
+	int error;
 
 	assert(wt);
 
-	if (!git_worktree_is_locked(NULL, wt))
+	if ((error = git_worktree_is_locked(NULL, wt)) < 0)
+		return error;
+	if (!error)
 		return 1;
 
 	if (git_buf_joinpath(&path, wt->gitdir_path, "locked") < 0)
@@ -454,22 +464,25 @@ int git_worktree_unlock(git_worktree *wt)
 int git_worktree_is_locked(git_buf *reason, const git_worktree *wt)
 {
 	git_buf path = GIT_BUF_INIT;
-	int ret;
+	int error, locked;
 
 	assert(wt);
 
 	if (reason)
 		git_buf_clear(reason);
 
-	if ((ret = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
+	if ((error = git_buf_joinpath(&path, wt->gitdir_path, "locked")) < 0)
+		goto out;
+	locked = git_path_exists(path.ptr);
+	if (locked && reason &&
+	    (error = git_futils_readbuffer(reason, path.ptr)) < 0)
 		goto out;
-	if ((ret = git_path_exists(path.ptr)) && reason)
-		git_futils_readbuffer(reason, path.ptr);
 
+	error = locked;
 out:
 	git_buf_dispose(&path);
 
-	return ret;
+	return error;
 }
 
 const char *git_worktree_name(const git_worktree *wt)
@@ -502,7 +515,6 @@ int git_worktree_pruneinit_options(git_worktree_prune_options *opts,
 int git_worktree_is_prunable(git_worktree *wt,
 	git_worktree_prune_options *opts)
 {
-	git_buf reason = GIT_BUF_INIT;
 	git_worktree_prune_options popts = GIT_WORKTREE_PRUNE_OPTIONS_INIT;
 
 	GIT_ERROR_CHECK_VERSION(
@@ -512,20 +524,24 @@ int git_worktree_is_prunable(git_worktree *wt,
 	if (opts)
 		memcpy(&popts, opts, sizeof(popts));
 
-	if ((popts.flags & GIT_WORKTREE_PRUNE_LOCKED) == 0 &&
-		git_worktree_is_locked(&reason, wt))
-	{
-		if (!reason.size)
-			git_buf_attach_notowned(&reason, "no reason given", 15);
-		git_error_set(GIT_ERROR_WORKTREE, "not pruning locked working tree: '%s'", reason.ptr);
-		git_buf_dispose(&reason);
+	if ((popts.flags & GIT_WORKTREE_PRUNE_LOCKED) == 0) {
+		git_buf reason = GIT_BUF_INIT;
+		int error;
 
-		return 0;
+		if ((error = git_worktree_is_locked(&reason, wt)) < 0)
+			return error;
+
+		if (error) {
+			if (!reason.size)
+				git_buf_attach_notowned(&reason, "no reason given", 15);
+			git_error_set(GIT_ERROR_WORKTREE, "not pruning locked working tree: '%s'", reason.ptr);
+			git_buf_dispose(&reason);
+			return 0;
+		}
 	}
 
 	if ((popts.flags & GIT_WORKTREE_PRUNE_VALID) == 0 &&
-		git_worktree_validate(wt) == 0)
-	{
+	    git_worktree_validate(wt) == 0) {
 		git_error_set(GIT_ERROR_WORKTREE, "not pruning valid working tree");
 		return 0;
 	}