Fix repository discovery with ceiling_dirs at current directory

git only checks ceiling directories when its search ascends to a parent
directory.  A ceiling directory matching the starting directory will not
prevent git from finding a repository in the starting directory or a
parent directory.  libgit2 handled the former case correctly, but
differed from git in the latter case: given a ceiling directory matching
the starting directory, but no repository at the starting directory,
libgit2 would stop the search at that point rather than finding a
repository in a parent directory.

Test case using git command-line tools:

/tmp$ git init x
Initialized empty Git repository in /tmp/x/.git/
/tmp$ cd x/
/tmp/x$ mkdir subdir
/tmp/x$ cd subdir/
/tmp/x/subdir$ GIT_CEILING_DIRECTORIES=/tmp/x git rev-parse --git-dir
fatal: Not a git repository (or any of the parent directories): .git
/tmp/x/subdir$ GIT_CEILING_DIRECTORIES=/tmp/x/subdir git rev-parse --git-dir
/tmp/x/.git

Fix the testsuite to test this case (in one case fixing a test that
depended on the current behavior), and then fix find_repo to handle this
case correctly.

In the process, simplify and document the logic in find_repo():
- Separate the concepts of "currently checking a .git directory" and
  "number of iterations left before going further counts as a search"
  into two separate variables, in_dot_git and min_iterations.
- Move the logic to handle in_dot_git and append /.git to the top of the
  loop.
- Only search ceiling_dirs and find ceiling_offset after running out of
  min_iterations; since ceiling_offset only tracks the longest matching
  ceiling directory, if ceiling_dirs contained both the current
  directory and a parent directory, this change makes find_repo stop the
  search at the parent directory.

src/repository.c

@@ -359,7 +359,8 @@ static int find_repo(
 	git_buf path = GIT_BUF_INIT;
 	struct stat st;
 	dev_t initial_device = 0;
-	bool try_with_dot_git = ((flags & GIT_REPOSITORY_OPEN_BARE) != 0);
+	int min_iterations;
+	bool in_dot_git;
 	int ceiling_offset;
 
 	git_buf_free(repo_path);
@@ -367,13 +368,27 @@ static int find_repo(
 	if ((error = git_path_prettify(&path, start_path, NULL)) < 0)
 		return error;
 
-	ceiling_offset = find_ceiling_dir_offset(path.ptr, ceiling_dirs);
+	/* in_dot_git toggles each loop:
+	 * /a/b/c/.git, /a/b/c, /a/b/.git, /a/b, /a/.git, /a
+	 * With GIT_REPOSITORY_OPEN_BARE, we assume we started with /a/b/c.git
+	 * and don't append .git the first time through.
+	 * min_iterations indicates the number of iterations left before going
+	 * further counts as a search. */
+	if (flags & GIT_REPOSITORY_OPEN_BARE) {
+		in_dot_git = true;
+		min_iterations = 1;
+	} else {
+		in_dot_git = false;
+		min_iterations = 2;
+	}
 
-	if (!try_with_dot_git &&
-		(error = git_buf_joinpath(&path, path.ptr, DOT_GIT)) < 0)
-		return error;
+	while (!error && (min_iterations || !(path.ptr[ceiling_offset] == 0 ||
+					      (flags & GIT_REPOSITORY_OPEN_NO_SEARCH)))) {
+		if (!in_dot_git)
+			if ((error = git_buf_joinpath(&path, path.ptr, DOT_GIT)) < 0)
+				break;
+		in_dot_git = !in_dot_git;
 
-	while (!error && !git_buf_len(repo_path)) {
 		if (p_stat(path.ptr, &st) == 0) {
 			/* check that we have not crossed device boundaries */
 			if (initial_device == 0)
@@ -414,17 +429,10 @@ static int find_repo(
 			break;
 		}
 
-		if (try_with_dot_git) {
-			/* if we tried original dir with and without .git AND either hit
-			 * directory ceiling or NO_SEARCH was requested, then be done.
-			 */
-			if (path.ptr[ceiling_offset] == '\0' ||
-				(flags & GIT_REPOSITORY_OPEN_NO_SEARCH) != 0)
-				break;
-			/* otherwise look first for .git item */
-			error = git_buf_joinpath(&path, path.ptr, DOT_GIT);
-		}
-		try_with_dot_git = !try_with_dot_git;
+		/* Once we've checked the directory (and .git if applicable),
+		 * find the ceiling for a search. */
+		if (min_iterations && (--min_iterations == 0))
+			ceiling_offset = find_ceiling_dir_offset(path.ptr, ceiling_dirs);
 	}
 
 	if (!error && parent_path && !(flags & GIT_REPOSITORY_OPEN_BARE)) {

tests/repo/discover.c

@@ -118,12 +118,22 @@ void test_repo_discover__0(void)
 	cl_git_fail(git_repository_discover(&found_path, ALTERNATE_MALFORMED_FOLDER3, 0, ceiling_dirs));
 	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, ALTERNATE_NOT_FOUND_FOLDER, 0, ceiling_dirs));
 
+	append_ceiling_dir(&ceiling_dirs_buf, SUB_REPOSITORY_FOLDER_SUB);
+	ceiling_dirs = git_buf_cstr(&ceiling_dirs_buf);
+
+	/* this must pass as ceiling_directories cannot prevent the current
+	 * working directory to be checked */
+	ensure_repository_discover(SUB_REPOSITORY_FOLDER, ceiling_dirs, &sub_repository_path);
+	ensure_repository_discover(SUB_REPOSITORY_FOLDER_SUB, ceiling_dirs, &sub_repository_path);
+	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER_SUB_SUB, 0, ceiling_dirs));
+	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER_SUB_SUB_SUB, 0, ceiling_dirs));
+
 	append_ceiling_dir(&ceiling_dirs_buf, SUB_REPOSITORY_FOLDER);
 	ceiling_dirs = git_buf_cstr(&ceiling_dirs_buf);
 
 	//this must pass as ceiling_directories cannot predent the current
 	//working directory to be checked
-	cl_git_pass(git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER, 0, ceiling_dirs));
+	ensure_repository_discover(SUB_REPOSITORY_FOLDER, ceiling_dirs, &sub_repository_path);
 	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER_SUB, 0, ceiling_dirs));
 	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER_SUB_SUB, 0, ceiling_dirs));
 	cl_assert_equal_i(GIT_ENOTFOUND, git_repository_discover(&found_path, SUB_REPOSITORY_FOLDER_SUB_SUB_SUB, 0, ceiling_dirs));

tests/repo/open.c

@@ -196,8 +196,9 @@ void test_repo_open__failures(void)
 		&repo, "attr/sub", GIT_REPOSITORY_OPEN_NO_SEARCH, NULL));
 
 	/* fail with ceiling too low */
-	cl_git_pass(git_buf_joinpath(&ceiling, ceiling.ptr, "sub"));
 	cl_git_fail(git_repository_open_ext(&repo, "attr/sub", 0, ceiling.ptr));
+	cl_git_pass(git_buf_joinpath(&ceiling, ceiling.ptr, "sub"));
+	cl_git_fail(git_repository_open_ext(&repo, "attr/sub/sub", 0, ceiling.ptr));
 
 	/* fail with no repo */
 	cl_git_pass(p_mkdir("alternate", 0777));