Add GIT_REPOSITORY_OPEN_FROM_ENV flag to respect $GIT_* environment vars

git_repository_open_ext provides parameters for the start path, whether
to search across filesystems, and what ceiling directories to stop at.
git commands have standard environment variables and defaults for each
of those, as well as various other parameters of the repository. To
avoid duplicate environment variable handling in users of libgit2, add a
GIT_REPOSITORY_OPEN_FROM_ENV flag, which makes git_repository_open_ext
automatically handle the appropriate environment variables. Commands
that intend to act just like those built into git itself can use this
flag to get the expected default behavior.

git_repository_open_ext with the GIT_REPOSITORY_OPEN_FROM_ENV flag
respects $GIT_DIR, $GIT_DISCOVERY_ACROSS_FILESYSTEM,
$GIT_CEILING_DIRECTORIES, $GIT_INDEX_FILE, $GIT_NAMESPACE,
$GIT_OBJECT_DIRECTORY, and $GIT_ALTERNATE_OBJECT_DIRECTORIES.  In the
future, when libgit2 gets worktree support, git_repository_open_env will
also respect $GIT_WORK_TREE and $GIT_COMMON_DIR; until then,
git_repository_open_ext with this flag will error out if either
$GIT_WORK_TREE or $GIT_COMMON_DIR is set.

3 files changed, 443 insertions, 1 deletions

diff --git a/include/git2/repository.h b/include/git2/repository.h
index f7efe0116..3d70d1b89 100644
--- a/include/git2/repository.h
+++ b/include/git2/repository.h
@@ -98,12 +98,26 @@ GIT_EXTERN(int) git_repository_discover(
  * * GIT_REPOSITORY_OPEN_NO_DOTGIT - Do not check for a repository by
  *   appending /.git to the start_path; only open the repository if
  *   start_path itself points to the git directory.
+ * * GIT_REPOSITORY_OPEN_FROM_ENV - Find and open a git repository,
+ *   respecting the environment variables used by the git command-line
+ *   tools. If set, `git_repository_open_ext` will ignore the other
+ *   flags and the `ceiling_dirs` argument, and will allow a NULL `path`
+ *   to use `GIT_DIR` or search from the current directory. The search
+ *   for a repository will respect $GIT_CEILING_DIRECTORIES and
+ *   $GIT_DISCOVERY_ACROSS_FILESYSTEM.  The opened repository will
+ *   respect $GIT_INDEX_FILE, $GIT_NAMESPACE, $GIT_OBJECT_DIRECTORY, and
+ *   $GIT_ALTERNATE_OBJECT_DIRECTORIES.  In the future, this flag will
+ *   also cause `git_repository_open_ext` to respect $GIT_WORK_TREE and
+ *   $GIT_COMMON_DIR; currently, `git_repository_open_ext` with this
+ *   flag will error out if either $GIT_WORK_TREE or $GIT_COMMON_DIR is
+ *   set.
  */
 typedef enum {
 	GIT_REPOSITORY_OPEN_NO_SEARCH = (1 << 0),
 	GIT_REPOSITORY_OPEN_CROSS_FS  = (1 << 1),
 	GIT_REPOSITORY_OPEN_BARE      = (1 << 2),
 	GIT_REPOSITORY_OPEN_NO_DOTGIT = (1 << 3),
+	GIT_REPOSITORY_OPEN_FROM_ENV  = (1 << 4),
 } git_repository_open_flag_t;
 
 /**
@@ -114,7 +128,8 @@ typedef enum {
  *        see if a repo at this path could be opened.
  * @param path Path to open as git repository.  If the flags
  *        permit "searching", then this can be a path to a subdirectory
- *        inside the working directory of the repository.
+ *        inside the working directory of the repository. May be NULL if
+ *        flags is GIT_REPOSITORY_OPEN_FROM_ENV.
  * @param flags A combination of the GIT_REPOSITORY_OPEN flags above.
  * @param ceiling_dirs A GIT_PATH_LIST_SEPARATOR delimited list of path
  *        prefixes at which the search for a containing repository should
diff --git a/src/repository.c b/src/repository.c
index 5b4346793..635b13b84 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -491,6 +491,172 @@ int git_repository_open_bare(
 	return 0;
 }
 
+static int _git_repository_open_ext_from_env(
+	git_repository **out,
+	const char *start_path)
+{
+	git_repository *repo = NULL;
+	git_index *index = NULL;
+	git_odb *odb = NULL;
+	git_buf dir_buf = GIT_BUF_INIT;
+	git_buf ceiling_dirs_buf = GIT_BUF_INIT;
+	git_buf across_fs_buf = GIT_BUF_INIT;
+	git_buf index_file_buf = GIT_BUF_INIT;
+	git_buf namespace_buf = GIT_BUF_INIT;
+	git_buf object_dir_buf = GIT_BUF_INIT;
+	git_buf alts_buf = GIT_BUF_INIT;
+	git_buf work_tree_buf = GIT_BUF_INIT;
+	git_buf common_dir_buf = GIT_BUF_INIT;
+	const char *ceiling_dirs = NULL;
+	unsigned flags = 0;
+	int error;
+
+	if (!start_path) {
+		error = git__getenv(&dir_buf, "GIT_DIR");
+		if (error == GIT_ENOTFOUND) {
+			giterr_clear();
+			start_path = ".";
+		} else if (error < 0)
+			goto error;
+		else {
+			start_path = git_buf_cstr(&dir_buf);
+			flags |= GIT_REPOSITORY_OPEN_NO_SEARCH;
+			flags |= GIT_REPOSITORY_OPEN_NO_DOTGIT;
+		}
+	}
+
+	error = git__getenv(&ceiling_dirs_buf, "GIT_CEILING_DIRECTORIES");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else
+		ceiling_dirs = git_buf_cstr(&ceiling_dirs_buf);
+
+	error = git__getenv(&across_fs_buf, "GIT_DISCOVERY_ACROSS_FILESYSTEM");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else {
+		int across_fs = 0;
+		error = git_config_parse_bool(&across_fs, git_buf_cstr(&across_fs_buf));
+		if (error < 0)
+			goto error;
+		if (across_fs)
+			flags |= GIT_REPOSITORY_OPEN_CROSS_FS;
+	}
+
+	error = git__getenv(&index_file_buf, "GIT_INDEX_FILE");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else {
+		error = git_index_open(&index, git_buf_cstr(&index_file_buf));
+		if (error < 0)
+			goto error;
+	}
+
+	error = git__getenv(&namespace_buf, "GIT_NAMESPACE");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+
+	error = git__getenv(&object_dir_buf, "GIT_OBJECT_DIRECTORY");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else {
+		error = git_odb_open(&odb, git_buf_cstr(&object_dir_buf));
+		if (error < 0)
+			goto error;
+	}
+
+	error = git__getenv(&work_tree_buf, "GIT_WORK_TREE");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else {
+		giterr_set(GITERR_INVALID, "GIT_WORK_TREE unimplemented");
+		error = GIT_ERROR;
+		goto error;
+	}
+
+	error = git__getenv(&work_tree_buf, "GIT_COMMON_DIR");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+	else {
+		giterr_set(GITERR_INVALID, "GIT_COMMON_DIR unimplemented");
+		error = GIT_ERROR;
+		goto error;
+	}
+
+	error = git_repository_open_ext(&repo, start_path, flags, ceiling_dirs);
+	if (error < 0)
+		goto error;
+
+	if (odb)
+		git_repository_set_odb(repo, odb);
+
+	error = git__getenv(&alts_buf, "GIT_ALTERNATE_OBJECT_DIRECTORIES");
+	if (error == GIT_ENOTFOUND)
+		giterr_clear();
+	else if (error < 0)
+		goto error;
+        else {
+		const char *end;
+		char *alt, *sep;
+		if (!odb) {
+			error = git_repository_odb(&odb, repo);
+			if (error < 0)
+				goto error;
+		}
+
+		end = git_buf_cstr(&alts_buf) + git_buf_len(&alts_buf);
+		for (sep = alt = alts_buf.ptr; sep != end; alt = sep+1) {
+			for (sep = alt; *sep && *sep != GIT_PATH_LIST_SEPARATOR; sep++)
+				;
+			if (*sep)
+				*sep = '\0';
+			error = git_odb_add_disk_alternate(odb, alt);
+			if (error < 0)
+				goto error;
+		}
+	}
+
+	error = git_repository_set_namespace(repo, git_buf_cstr(&namespace_buf));
+	if (error < 0)
+		goto error;
+
+	git_repository_set_index(repo, index);
+
+	if (out) {
+		*out = repo;
+		goto success;
+	}
+error:
+	git_repository_free(repo);
+success:
+	git_odb_free(odb);
+	git_index_free(index);
+	git_buf_free(&common_dir_buf);
+	git_buf_free(&work_tree_buf);
+	git_buf_free(&alts_buf);
+	git_buf_free(&object_dir_buf);
+	git_buf_free(&namespace_buf);
+	git_buf_free(&index_file_buf);
+	git_buf_free(&across_fs_buf);
+	git_buf_free(&ceiling_dirs_buf);
+	git_buf_free(&dir_buf);
+	return error;
+}
+
 int git_repository_open_ext(
 	git_repository **repo_ptr,
 	const char *start_path,
@@ -503,6 +669,9 @@ int git_repository_open_ext(
 	git_repository *repo;
 	git_config *config = NULL;
 
+	if (flags & GIT_REPOSITORY_OPEN_FROM_ENV)
+		return _git_repository_open_ext_from_env(repo_ptr, start_path);
+
 	if (repo_ptr)
 		*repo_ptr = NULL;
 
diff --git a/tests/repo/open.c b/tests/repo/open.c
index 5197276fb..86353dd25 100644
--- a/tests/repo/open.c
+++ b/tests/repo/open.c
@@ -3,12 +3,42 @@
 #include "sysdir.h"
 #include <ctype.h>
 
+static void clear_git_env(void)
+{
+	cl_setenv("GIT_DIR", NULL);
+	cl_setenv("GIT_CEILING_DIRECTORIES", NULL);
+	cl_setenv("GIT_INDEX_FILE", NULL);
+	cl_setenv("GIT_NAMESPACE", NULL);
+	cl_setenv("GIT_OBJECT_DIRECTORY", NULL);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", NULL);
+	cl_setenv("GIT_WORK_TREE", NULL);
+	cl_setenv("GIT_COMMON_DIR", NULL);
+}
+
+static git_buf cwd_backup_buf = GIT_BUF_INIT;
+
+void test_repo_open__initialize(void)
+{
+	if (!git_buf_is_allocated(&cwd_backup_buf))
+		cl_git_pass(git_path_prettify_dir(&cwd_backup_buf, ".", NULL));
+	clear_git_env();
+}
+
 void test_repo_open__cleanup(void)
 {
 	cl_git_sandbox_cleanup();
 
 	if (git_path_isdir("alternate"))
 		git_futils_rmdir_r("alternate", NULL, GIT_RMDIR_REMOVE_FILES);
+	if (git_path_isdir("attr"))
+		git_futils_rmdir_r("attr", NULL, GIT_RMDIR_REMOVE_FILES);
+	if (git_path_isdir("testrepo.git"))
+		git_futils_rmdir_r("testrepo.git", NULL, GIT_RMDIR_REMOVE_FILES);
+	if (git_path_isdir("peeled.git"))
+		git_futils_rmdir_r("peeled.git", NULL, GIT_RMDIR_REMOVE_FILES);
+
+	cl_must_pass(p_chdir(git_buf_cstr(&cwd_backup_buf)));
+	clear_git_env();
 }
 
 void test_repo_open__bare_empty_repo(void)
@@ -401,3 +431,231 @@ void test_repo_open__force_bare(void)
 	cl_assert(git_repository_is_bare(barerepo));
 	git_repository_free(barerepo);
 }
+
+static int GIT_FORMAT_PRINTF(2, 3) cl_setenv_printf(const char *name, const char *fmt, ...)
+{
+	int ret;
+	va_list args;
+	git_buf buf = GIT_BUF_INIT;
+
+	va_start(args, fmt);
+	cl_git_pass(git_buf_vprintf(&buf, fmt, args));
+	va_end(args);
+
+	ret = cl_setenv(name, git_buf_cstr(&buf));
+	git_buf_free(&buf);
+	return ret;
+}
+
+/* Helper functions for test_repo_open__env, passing through the file and line
+ * from the caller rather than those of the helper. The expression strings
+ * distinguish between the possible failures within the helper. */
+
+static void env_pass_(const char *path, const char *file, int line)
+{
+	git_repository *repo;
+	cl_git_pass_(git_repository_open_ext(NULL, path, GIT_REPOSITORY_OPEN_FROM_ENV, NULL), file, line);
+	cl_git_pass_(git_repository_open_ext(&repo, path, GIT_REPOSITORY_OPEN_FROM_ENV, NULL), file, line);
+	cl_assert_at_line(git__suffixcmp(git_repository_path(repo), "attr/.git/") == 0, file, line);
+	cl_assert_at_line(git__suffixcmp(git_repository_workdir(repo), "attr/") == 0, file, line);
+	cl_assert_at_line(!git_repository_is_bare(repo), file, line);
+	git_repository_free(repo);
+}
+#define env_pass(path) env_pass_((path), __FILE__, __LINE__)
+
+#define cl_git_fail_at_line(expr, file, line) clar__assert((expr) < 0, file, line, "Expected function call to fail: " #expr, NULL, 1)
+
+static void env_fail_(const char *path, const char *file, int line)
+{
+	git_repository *repo;
+	cl_git_fail_at_line(git_repository_open_ext(NULL, path, GIT_REPOSITORY_OPEN_FROM_ENV, NULL), file, line);
+	cl_git_fail_at_line(git_repository_open_ext(&repo, path, GIT_REPOSITORY_OPEN_FROM_ENV, NULL), file, line);
+}
+#define env_fail(path) env_fail_((path), __FILE__, __LINE__)
+
+static void env_cd_(
+	const char *path,
+	void (*passfail_)(const char *, const char *, int),
+	const char *file, int line)
+{
+	git_buf cwd_buf = GIT_BUF_INIT;
+	cl_git_pass(git_path_prettify_dir(&cwd_buf, ".", NULL));
+	cl_must_pass(p_chdir(path));
+	passfail_(NULL, file, line);
+	cl_must_pass(p_chdir(git_buf_cstr(&cwd_buf)));
+}
+#define env_cd_pass(path) env_cd_((path), env_pass_, __FILE__, __LINE__)
+#define env_cd_fail(path) env_cd_((path), env_fail_, __FILE__, __LINE__)
+
+static void env_check_objects_(bool a, bool t, bool p, const char *file, int line)
+{
+	git_repository *repo;
+	git_oid oid_a, oid_t, oid_p;
+	git_object *object;
+	cl_git_pass(git_oid_fromstr(&oid_a, "45141a79a77842c59a63229403220a4e4be74e3d"));
+	cl_git_pass(git_oid_fromstr(&oid_t, "1385f264afb75a56a5bec74243be9b367ba4ca08"));
+	cl_git_pass(git_oid_fromstr(&oid_p, "0df1a5865c8abfc09f1f2182e6a31be550e99f07"));
+	cl_git_pass_(git_repository_open_ext(&repo, "attr", GIT_REPOSITORY_OPEN_FROM_ENV, NULL), file, line);
+	if (a) {
+		cl_git_pass_(git_object_lookup(&object, repo, &oid_a, GIT_OBJ_BLOB), file, line);
+		git_object_free(object);
+	} else
+		cl_git_fail_at_line(git_object_lookup(&object, repo, &oid_a, GIT_OBJ_BLOB), file, line);
+	if (t) {
+		cl_git_pass_(git_object_lookup(&object, repo, &oid_t, GIT_OBJ_BLOB), file, line);
+		git_object_free(object);
+	} else
+		cl_git_fail_at_line(git_object_lookup(&object, repo, &oid_t, GIT_OBJ_BLOB), file, line);
+	if (p) {
+		cl_git_pass_(git_object_lookup(&object, repo, &oid_p, GIT_OBJ_COMMIT), file, line);
+		git_object_free(object);
+	} else
+		cl_git_fail_at_line(git_object_lookup(&object, repo, &oid_p, GIT_OBJ_COMMIT), file, line);
+	git_repository_free(repo);
+}
+#define env_check_objects(a, t, t2) env_check_objects_((a), (t), (t2), __FILE__, __LINE__)
+
+void test_repo_open__env(void)
+{
+	git_repository *repo = NULL;
+	git_buf repo_dir_buf = GIT_BUF_INIT;
+	const char *repo_dir = NULL;
+	git_index *index = NULL;
+	const char *t_obj = "testrepo.git/objects";
+	const char *p_obj = "peeled.git/objects";
+
+	cl_fixture_sandbox("attr");
+	cl_fixture_sandbox("testrepo.git");
+	cl_fixture_sandbox("peeled.git");
+	cl_git_pass(p_rename("attr/.gitted", "attr/.git"));
+
+	cl_git_pass(git_path_prettify_dir(&repo_dir_buf, "attr", NULL));
+	repo_dir = git_buf_cstr(&repo_dir_buf);
+
+	/* GIT_DIR that doesn't exist */
+	cl_setenv("GIT_DIR", "does-not-exist");
+	env_fail(NULL);
+	/* Explicit start_path overrides GIT_DIR */
+	env_pass("attr");
+	env_pass("attr/.git");
+	env_pass("attr/sub");
+	env_pass("attr/sub/sub");
+
+	/* GIT_DIR with relative paths */
+	cl_setenv("GIT_DIR", "attr/.git");
+	env_pass(NULL);
+	cl_setenv("GIT_DIR", "attr");
+	env_fail(NULL);
+	cl_setenv("GIT_DIR", "attr/sub");
+	env_fail(NULL);
+	cl_setenv("GIT_DIR", "attr/sub/sub");
+	env_fail(NULL);
+
+        /* GIT_DIR with absolute paths */
+	cl_setenv_printf("GIT_DIR", "%s/.git", repo_dir);
+	env_pass(NULL);
+	cl_setenv("GIT_DIR", repo_dir);
+	env_fail(NULL);
+	cl_setenv_printf("GIT_DIR", "%s/sub", repo_dir);
+	env_fail(NULL);
+	cl_setenv_printf("GIT_DIR", "%s/sub/sub", repo_dir);
+	env_fail(NULL);
+	cl_setenv("GIT_DIR", NULL);
+
+	/* Searching from the current directory */
+	env_cd_pass("attr");
+	env_cd_pass("attr/.git");
+	env_cd_pass("attr/sub");
+	env_cd_pass("attr/sub/sub");
+
+	/* A ceiling directory blocks searches from ascending into that
+	 * directory, but doesn't block the start_path itself. */
+	cl_setenv("GIT_CEILING_DIRECTORIES", repo_dir);
+	env_cd_pass("attr");
+	env_cd_fail("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+	cl_setenv_printf("GIT_CEILING_DIRECTORIES", "%s/sub", repo_dir);
+	env_cd_pass("attr");
+	env_cd_pass("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+        /* Multiple ceiling directories */
+	cl_setenv_printf("GIT_CEILING_DIRECTORIES", "123%c%s/sub%cabc",
+		GIT_PATH_LIST_SEPARATOR, repo_dir, GIT_PATH_LIST_SEPARATOR);
+	env_cd_pass("attr");
+	env_cd_pass("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+	cl_setenv_printf("GIT_CEILING_DIRECTORIES", "%s%c%s/sub",
+		repo_dir, GIT_PATH_LIST_SEPARATOR, repo_dir);
+	env_cd_pass("attr");
+	env_cd_fail("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+	cl_setenv_printf("GIT_CEILING_DIRECTORIES", "%s/sub%c%s",
+		repo_dir, GIT_PATH_LIST_SEPARATOR, repo_dir);
+	env_cd_pass("attr");
+	env_cd_fail("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+	cl_setenv_printf("GIT_CEILING_DIRECTORIES", "%s%c%s/sub/sub",
+		repo_dir, GIT_PATH_LIST_SEPARATOR, repo_dir);
+	env_cd_pass("attr");
+	env_cd_fail("attr/sub");
+	env_cd_fail("attr/sub/sub");
+
+	cl_setenv("GIT_CEILING_DIRECTORIES", NULL);
+
+        /* Index files */
+	cl_setenv("GIT_INDEX_FILE", cl_fixture("gitgit.index"));
+	cl_git_pass(git_repository_open_ext(&repo, "attr", GIT_REPOSITORY_OPEN_FROM_ENV, NULL));
+	cl_git_pass(git_repository_index(&index, repo));
+	cl_assert_equal_s(git_index_path(index), cl_fixture("gitgit.index"));
+	cl_assert_equal_i(git_index_entrycount(index), 1437);
+	git_index_free(index);
+	git_repository_free(repo);
+	cl_setenv("GIT_INDEX_FILE", NULL);
+
+        /* Namespaces */
+	cl_setenv("GIT_NAMESPACE", "some-namespace");
+	cl_git_pass(git_repository_open_ext(&repo, "attr", GIT_REPOSITORY_OPEN_FROM_ENV, NULL));
+	cl_assert_equal_s(git_repository_get_namespace(repo), "some-namespace");
+	git_repository_free(repo);
+	cl_setenv("GIT_NAMESPACE", NULL);
+
+        /* Object directories and alternates */
+	env_check_objects(true, false, false);
+
+	cl_setenv("GIT_OBJECT_DIRECTORY", t_obj);
+	env_check_objects(false, true, false);
+	cl_setenv("GIT_OBJECT_DIRECTORY", NULL);
+
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", t_obj);
+	env_check_objects(true, true, false);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", NULL);
+
+	cl_setenv("GIT_OBJECT_DIRECTORY", p_obj);
+	env_check_objects(false, false, true);
+	cl_setenv("GIT_OBJECT_DIRECTORY", NULL);
+
+	cl_setenv("GIT_OBJECT_DIRECTORY", t_obj);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", p_obj);
+	env_check_objects(false, true, true);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", NULL);
+	cl_setenv("GIT_OBJECT_DIRECTORY", NULL);
+
+	cl_setenv_printf("GIT_ALTERNATE_OBJECT_DIRECTORIES",
+			"%s%c%s", t_obj, GIT_PATH_LIST_SEPARATOR, p_obj);
+	env_check_objects(true, true, true);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", NULL);
+
+	cl_setenv_printf("GIT_ALTERNATE_OBJECT_DIRECTORIES",
+			"%s%c%s", p_obj, GIT_PATH_LIST_SEPARATOR, t_obj);
+	env_check_objects(true, true, true);
+	cl_setenv("GIT_ALTERNATE_OBJECT_DIRECTORIES", NULL);
+
+	cl_fixture_cleanup("peeled.git");
+	cl_fixture_cleanup("testrepo.git");
+	cl_fixture_cleanup("attr");
+}