Merge branch 'js/early-config'

The start-up sequence of "git" needs to figure out some configured
settings before it finds and set itself up in the location of the
repository and was quite messy due to its "chicken-and-egg" nature.
The code has been restructured.

* js/early-config:
  setup.c: mention unresolved problems
  t1309: document cases where we would want early config not to die()
  setup_git_directory_gently_1(): avoid die()ing
  t1309: test read_early_config()
  read_early_config(): really discover .git/
  read_early_config(): avoid .git/config hack when unneeded
  setup: make read_early_config() reusable
  setup: introduce the discover_git_directory() function
  setup_git_directory_1(): avoid changing global state
  setup: prepare setup_discovered_git_dir() for the root directory
  setup_git_directory(): use is_dir_sep() helper
  t7006: replace dubious test

7 files changed, 313 insertions, 111 deletions

diff --git a/cache.h b/cache.h
index 26f336b00f..9b2157f591 100644
--- a/cache.h
+++ b/cache.h
@@ -518,6 +518,13 @@ extern void set_git_work_tree(const char *tree);
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
 extern void setup_work_tree(void);
+/*
+ * Find GIT_DIR of the repository that contains the current working directory,
+ * without changing the working directory or other global state. The result is
+ * appended to gitdir. The return value is either NULL if no repository was
+ * found, or pointing to the path inside gitdir's buffer.
+ */
+extern const char *discover_git_directory(struct strbuf *gitdir);
 extern const char *setup_git_directory_gently(int *);
 extern const char *setup_git_directory(void);
 extern char *prefix_path(const char *prefix, int len, const char *path);
@@ -1842,6 +1849,7 @@ extern int git_config_from_blob_sha1(config_fn_t fn, const char *name,
 				     const unsigned char *sha1, void *data);
 extern void git_config_push_parameter(const char *text);
 extern int git_config_from_parameters(config_fn_t fn, void *data);
+extern void read_early_config(config_fn_t cb, void *data);
 extern void git_config(config_fn_t fn, void *);
 extern int git_config_with_options(config_fn_t fn, void *,
 				   struct git_config_source *config_source,
diff --git a/config.c b/config.c
index bd286b3e36..eb7e310a11 100644
--- a/config.c
+++ b/config.c
@@ -1503,6 +1503,31 @@ static void configset_iter(struct config_set *cs, config_fn_t fn, void *data)
 	}
 }
 
+void read_early_config(config_fn_t cb, void *data)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	git_config_with_options(cb, data, NULL, 1);
+
+	/*
+	 * When setup_git_directory() was not yet asked to discover the
+	 * GIT_DIR, we ask discover_git_directory() to figure out whether there
+	 * is any repository config we should use (but unlike
+	 * setup_git_directory_gently(), no global state is changed, most
+	 * notably, the current working directory is still the same after the
+	 * call).
+	 */
+	if (!have_git_dir() && discover_git_directory(&buf)) {
+		struct git_config_source repo_config;
+
+		memset(&repo_config, 0, sizeof(repo_config));
+		strbuf_addstr(&buf, "/config");
+		repo_config.file = buf.buf;
+		git_config_with_options(cb, data, &repo_config, 1);
+	}
+	strbuf_release(&buf);
+}
+
 static void git_config_check_init(void);
 
 void git_config(config_fn_t fn, void *data)
diff --git a/pager.c b/pager.c
index ae79643363..73ca8bc3b1 100644
--- a/pager.c
+++ b/pager.c
@@ -43,37 +43,6 @@ static int core_pager_config(const char *var, const char *value, void *data)
 	return 0;
 }
 
-static void read_early_config(config_fn_t cb, void *data)
-{
-	git_config_with_options(cb, data, NULL, 1);
-
-	/*
-	 * Note that this is a really dirty hack that does the wrong thing in
-	 * many cases. The crux of the problem is that we cannot run
-	 * setup_git_directory() early on in git's setup, so we have no idea if
-	 * we are in a repository or not, and therefore are not sure whether
-	 * and how to read repository-local config.
-	 *
-	 * So if we _aren't_ in a repository (or we are but we would reject its
-	 * core.repositoryformatversion), we'll read whatever is in .git/config
-	 * blindly. Similarly, if we _are_ in a repository, but not at the
-	 * root, we'll fail to find .git/config (because it's really
-	 * ../.git/config, etc). See t7006 for a complete set of failures.
-	 *
-	 * However, we have historically provided this hack because it does
-	 * work some of the time (namely when you are at the top-level of a
-	 * valid repository), and would rarely make things worse (i.e., you do
-	 * not generally have a .git/config file sitting around).
-	 */
-	if (!startup_info->have_repository) {
-		struct git_config_source repo_config;
-
-		memset(&repo_config, 0, sizeof(repo_config));
-		repo_config.file = ".git/config";
-		git_config_with_options(cb, data, &repo_config, 1);
-	}
-}
-
 const char *git_pager(int stdout_is_tty)
 {
 	const char *pager;
diff --git a/setup.c b/setup.c
index 8f64fbdfb2..64f922a937 100644
--- a/setup.c
+++ b/setup.c
@@ -531,6 +531,7 @@ const char *read_gitfile_gently(const char *path, int *return_error_code)
 	ssize_t len;
 
 	if (stat(path, &st)) {
+		/* NEEDSWORK: discern between ENOENT vs other errors */
 		error_code = READ_GITFILE_ERR_STAT_FAILED;
 		goto cleanup_return;
 	}
@@ -721,8 +722,10 @@ static const char *setup_discovered_git_dir(const char *gitdir,
 	if (offset == cwd->len)
 		return NULL;
 
-	/* Make "offset" point to past the '/', and add a '/' at the end */
-	offset++;
+	/* Make "offset" point past the '/' (already the case for root dirs) */
+	if (offset != offset_1st_component(cwd->buf))
+		offset++;
+	/* Add a '/' at the end */
 	strbuf_addch(cwd, '/');
 	return cwd->buf + offset;
 }
@@ -816,50 +819,51 @@ static int canonicalize_ceiling_entry(struct string_list_item *item,
 	}
 }
 
+enum discovery_result {
+	GIT_DIR_NONE = 0,
+	GIT_DIR_EXPLICIT,
+	GIT_DIR_DISCOVERED,
+	GIT_DIR_BARE,
+	/* these are errors */
+	GIT_DIR_HIT_CEILING = -1,
+	GIT_DIR_HIT_MOUNT_POINT = -2,
+	GIT_DIR_INVALID_GITFILE = -3
+};
+
 /*
  * We cannot decide in this function whether we are in the work tree or
  * not, since the config can only be read _after_ this function was called.
+ *
+ * Also, we avoid changing any global state (such as the current working
+ * directory) to allow early callers.
+ *
+ * The directory where the search should start needs to be passed in via the
+ * `dir` parameter; upon return, the `dir` buffer will contain the path of
+ * the directory where the search ended, and `gitdir` will contain the path of
+ * the discovered .git/ directory, if any. If `gitdir` is not absolute, it
+ * is relative to `dir` (i.e. *not* necessarily the cwd).
  */
-static const char *setup_git_directory_gently_1(int *nongit_ok)
+static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
+							  struct strbuf *gitdir,
+							  int die_on_error)
 {
 	const char *env_ceiling_dirs = getenv(CEILING_DIRECTORIES_ENVIRONMENT);
 	struct string_list ceiling_dirs = STRING_LIST_INIT_DUP;
-	static struct strbuf cwd = STRBUF_INIT;
-	const char *gitdirenv, *ret;
-	char *gitfile;
-	int offset, offset_parent, ceil_offset = -1;
+	const char *gitdirenv;
+	int ceil_offset = -1, min_offset = has_dos_drive_prefix(dir->buf) ? 3 : 1;
 	dev_t current_device = 0;
 	int one_filesystem = 1;
 
 	/*
-	 * We may have read an incomplete configuration before
-	 * setting-up the git directory. If so, clear the cache so
-	 * that the next queries to the configuration reload complete
-	 * configuration (including the per-repo config file that we
-	 * ignored previously).
-	 */
-	git_config_clear();
-
-	/*
-	 * Let's assume that we are in a git repository.
-	 * If it turns out later that we are somewhere else, the value will be
-	 * updated accordingly.
-	 */
-	if (nongit_ok)
-		*nongit_ok = 0;
-
-	if (strbuf_getcwd(&cwd))
-		die_errno(_("Unable to read current working directory"));
-	offset = cwd.len;
-
-	/*
 	 * If GIT_DIR is set explicitly, we're not going
 	 * to do any discovery, but we still do repository
 	 * validation.
 	 */
 	gitdirenv = getenv(GIT_DIR_ENVIRONMENT);
-	if (gitdirenv)
-		return setup_explicit_git_dir(gitdirenv, &cwd, nongit_ok);
+	if (gitdirenv) {
+		strbuf_addstr(gitdir, gitdirenv);
+		return GIT_DIR_EXPLICIT;
+	}
 
 	if (env_ceiling_dirs) {
 		int empty_entry_found = 0;
@@ -867,15 +871,15 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
 		string_list_split(&ceiling_dirs, env_ceiling_dirs, PATH_SEP, -1);
 		filter_string_list(&ceiling_dirs, 0,
 				   canonicalize_ceiling_entry, &empty_entry_found);
-		ceil_offset = longest_ancestor_length(cwd.buf, &ceiling_dirs);
+		ceil_offset = longest_ancestor_length(dir->buf, &ceiling_dirs);
 		string_list_clear(&ceiling_dirs, 0);
 	}
 
-	if (ceil_offset < 0 && has_dos_drive_prefix(cwd.buf))
-		ceil_offset = 1;
+	if (ceil_offset < 0)
+		ceil_offset = min_offset - 2;
 
 	/*
-	 * Test in the following order (relative to the cwd):
+	 * Test in the following order (relative to the dir):
 	 * - .git (file containing "gitdir: <path>")
 	 * - .git/
 	 * - ./ (bare)
@@ -887,61 +891,155 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
 	 */
 	one_filesystem = !git_env_bool("GIT_DISCOVERY_ACROSS_FILESYSTEM", 0);
 	if (one_filesystem)
-		current_device = get_device_or_die(".", NULL, 0);
+		current_device = get_device_or_die(dir->buf, NULL, 0);
 	for (;;) {
-		gitfile = (char*)read_gitfile(DEFAULT_GIT_DIR_ENVIRONMENT);
-		if (gitfile)
-			gitdirenv = gitfile = xstrdup(gitfile);
-		else {
-			if (is_git_directory(DEFAULT_GIT_DIR_ENVIRONMENT))
-				gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
+		int offset = dir->len, error_code = 0;
+
+		if (offset > min_offset)
+			strbuf_addch(dir, '/');
+		strbuf_addstr(dir, DEFAULT_GIT_DIR_ENVIRONMENT);
+		gitdirenv = read_gitfile_gently(dir->buf, die_on_error ?
+						NULL : &error_code);
+		if (!gitdirenv) {
+			if (die_on_error ||
+			    error_code == READ_GITFILE_ERR_NOT_A_FILE) {
+				/* NEEDSWORK: fail if .git is not file nor dir */
+				if (is_git_directory(dir->buf))
+					gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
+			} else if (error_code != READ_GITFILE_ERR_STAT_FAILED)
+				return GIT_DIR_INVALID_GITFILE;
 		}
-
+		strbuf_setlen(dir, offset);
 		if (gitdirenv) {
-			ret = setup_discovered_git_dir(gitdirenv,
-						       &cwd, offset,
-						       nongit_ok);
-			free(gitfile);
-			return ret;
+			strbuf_addstr(gitdir, gitdirenv);
+			return GIT_DIR_DISCOVERED;
 		}
-		free(gitfile);
 
-		if (is_git_directory("."))
-			return setup_bare_git_dir(&cwd, offset, nongit_ok);
-
-		offset_parent = offset;
-		while (--offset_parent > ceil_offset && cwd.buf[offset_parent] != '/');
-		if (offset_parent <= ceil_offset)
-			return setup_nongit(cwd.buf, nongit_ok);
-		if (one_filesystem) {
-			dev_t parent_device = get_device_or_die("..", cwd.buf,
-								offset);
-			if (parent_device != current_device) {
-				if (nongit_ok) {
-					if (chdir(cwd.buf))
-						die_errno(_("Cannot come back to cwd"));
-					*nongit_ok = 1;
-					return NULL;
-				}
-				strbuf_setlen(&cwd, offset);
-				die(_("Not a git repository (or any parent up to mount point %s)\n"
-				"Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set)."),
-				    cwd.buf);
-			}
-		}
-		if (chdir("..")) {
-			strbuf_setlen(&cwd, offset);
-			die_errno(_("Cannot change to '%s/..'"), cwd.buf);
+		if (is_git_directory(dir->buf)) {
+			strbuf_addstr(gitdir, ".");
+			return GIT_DIR_BARE;
 		}
-		offset = offset_parent;
+
+		if (offset <= min_offset)
+			return GIT_DIR_HIT_CEILING;
+
+		while (--offset > ceil_offset && !is_dir_sep(dir->buf[offset]))
+			; /* continue */
+		if (offset <= ceil_offset)
+			return GIT_DIR_HIT_CEILING;
+
+		strbuf_setlen(dir, offset > min_offset ?  offset : min_offset);
+		if (one_filesystem &&
+		    current_device != get_device_or_die(dir->buf, NULL, offset))
+			return GIT_DIR_HIT_MOUNT_POINT;
 	}
 }
 
+const char *discover_git_directory(struct strbuf *gitdir)
+{
+	struct strbuf dir = STRBUF_INIT, err = STRBUF_INIT;
+	size_t gitdir_offset = gitdir->len, cwd_len;
+	struct repository_format candidate;
+
+	if (strbuf_getcwd(&dir))
+		return NULL;
+
+	cwd_len = dir.len;
+	if (setup_git_directory_gently_1(&dir, gitdir, 0) <= 0) {
+		strbuf_release(&dir);
+		return NULL;
+	}
+
+	/*
+	 * The returned gitdir is relative to dir, and if dir does not reflect
+	 * the current working directory, we simply make the gitdir absolute.
+	 */
+	if (dir.len < cwd_len && !is_absolute_path(gitdir->buf + gitdir_offset)) {
+		/* Avoid a trailing "/." */
+		if (!strcmp(".", gitdir->buf + gitdir_offset))
+			strbuf_setlen(gitdir, gitdir_offset);
+		else
+			strbuf_addch(&dir, '/');
+		strbuf_insert(gitdir, gitdir_offset, dir.buf, dir.len);
+	}
+
+	strbuf_reset(&dir);
+	strbuf_addf(&dir, "%s/config", gitdir->buf + gitdir_offset);
+	read_repository_format(&candidate, dir.buf);
+	strbuf_release(&dir);
+
+	if (verify_repository_format(&candidate, &err) < 0) {
+		warning("ignoring git dir '%s': %s",
+			gitdir->buf + gitdir_offset, err.buf);
+		strbuf_release(&err);
+		return NULL;
+	}
+
+	return gitdir->buf + gitdir_offset;
+}
+
 const char *setup_git_directory_gently(int *nongit_ok)
 {
+	static struct strbuf cwd = STRBUF_INIT;
+	struct strbuf dir = STRBUF_INIT, gitdir = STRBUF_INIT;
 	const char *prefix;
 
-	prefix = setup_git_directory_gently_1(nongit_ok);
+	/*
+	 * We may have read an incomplete configuration before
+	 * setting-up the git directory. If so, clear the cache so
+	 * that the next queries to the configuration reload complete
+	 * configuration (including the per-repo config file that we
+	 * ignored previously).
+	 */
+	git_config_clear();
+
+	/*
+	 * Let's assume that we are in a git repository.
+	 * If it turns out later that we are somewhere else, the value will be
+	 * updated accordingly.
+	 */
+	if (nongit_ok)
+		*nongit_ok = 0;
+
+	if (strbuf_getcwd(&cwd))
+		die_errno(_("Unable to read current working directory"));
+	strbuf_addbuf(&dir, &cwd);
+
+	switch (setup_git_directory_gently_1(&dir, &gitdir, 1)) {
+	case GIT_DIR_NONE:
+		prefix = NULL;
+		break;
+	case GIT_DIR_EXPLICIT:
+		prefix = setup_explicit_git_dir(gitdir.buf, &cwd, nongit_ok);
+		break;
+	case GIT_DIR_DISCOVERED:
+		if (dir.len < cwd.len && chdir(dir.buf))
+			die(_("Cannot change to '%s'"), dir.buf);
+		prefix = setup_discovered_git_dir(gitdir.buf, &cwd, dir.len,
+						  nongit_ok);
+		break;
+	case GIT_DIR_BARE:
+		if (dir.len < cwd.len && chdir(dir.buf))
+			die(_("Cannot change to '%s'"), dir.buf);
+		prefix = setup_bare_git_dir(&cwd, dir.len, nongit_ok);
+		break;
+	case GIT_DIR_HIT_CEILING:
+		prefix = setup_nongit(cwd.buf, nongit_ok);
+		break;
+	case GIT_DIR_HIT_MOUNT_POINT:
+		if (nongit_ok) {
+			*nongit_ok = 1;
+			strbuf_release(&cwd);
+			strbuf_release(&dir);
+			return NULL;
+		}
+		die(_("Not a git repository (or any parent up to mount point %s)\n"
+		      "Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set)."),
+		    dir.buf);
+	default:
+		die("BUG: unhandled setup_git_directory_1() result");
+	}
+
 	if (prefix)
 		setenv(GIT_PREFIX_ENVIRONMENT, prefix, 1);
 	else
@@ -950,6 +1048,9 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	startup_info->have_repository = !nongit_ok || !*nongit_ok;
 	startup_info->prefix = prefix;
 
+	strbuf_release(&dir);
+	strbuf_release(&gitdir);
+
 	return prefix;
 }
 
diff --git a/t/helper/test-config.c b/t/helper/test-config.c
index 83a4f2ab86..8e3ed6a76c 100644
--- a/t/helper/test-config.c
+++ b/t/helper/test-config.c
@@ -66,6 +66,16 @@ static int iterate_cb(const char *var, const char *value, void *data)
 	return 0;
 }
 
+static int early_config_cb(const char *var, const char *value, void *vdata)
+{
+	const char *key = vdata;
+
+	if (!strcmp(key, var))
+		printf("%s\n", value);
+
+	return 0;
+}
+
 int cmd_main(int argc, const char **argv)
 {
 	int i, val;
@@ -73,6 +83,11 @@ int cmd_main(int argc, const char **argv)
 	const struct string_list *strptr;
 	struct config_set cs;
 
+	if (argc == 3 && !strcmp(argv[1], "read_early_config")) {
+		read_early_config(early_config_cb, (void *)argv[2]);
+		return 0;
+	}
+
 	setup_git_directory();
 
 	git_configset_init(&cs);
diff --git a/t/t1309-early-config.sh b/t/t1309-early-config.sh
new file mode 100755
index 0000000000..b97357b8ab
--- /dev/null
+++ b/t/t1309-early-config.sh
@@ -0,0 +1,74 @@
+#!/bin/sh
+
+test_description='Test read_early_config()'
+
+. ./test-lib.sh
+
+test_expect_success 'read early config' '
+	test_config early.config correct &&
+	test-config read_early_config early.config >output &&
+	test correct = "$(cat output)"
+'
+
+test_expect_success 'in a sub-directory' '
+	test_config early.config sub &&
+	mkdir -p sub &&
+	(
+		cd sub &&
+		test-config read_early_config early.config
+	) >output &&
+	test sub = "$(cat output)"
+'
+
+test_expect_success 'ceiling' '
+	test_config early.config ceiling &&
+	mkdir -p sub &&
+	(
+		GIT_CEILING_DIRECTORIES="$PWD" &&
+		export GIT_CEILING_DIRECTORIES &&
+		cd sub &&
+		test-config read_early_config early.config
+	) >output &&
+	test -z "$(cat output)"
+'
+
+test_expect_success 'ceiling #2' '
+	mkdir -p xdg/git &&
+	git config -f xdg/git/config early.config xdg &&
+	test_config early.config ceiling &&
+	mkdir -p sub &&
+	(
+		XDG_CONFIG_HOME="$PWD"/xdg &&
+		GIT_CEILING_DIRECTORIES="$PWD" &&
+		export GIT_CEILING_DIRECTORIES XDG_CONFIG_HOME &&
+		cd sub &&
+		test-config read_early_config early.config
+	) >output &&
+	test xdg = "$(cat output)"
+'
+
+test_with_config () {
+	rm -rf throwaway &&
+	git init throwaway &&
+	(
+		cd throwaway &&
+		echo "$*" >.git/config &&
+		test-config read_early_config early.config
+	)
+}
+
+test_expect_success 'ignore .git/ with incompatible repository version' '
+	test_with_config "[core]repositoryformatversion = 999999" 2>err &&
+	grep "warning:.* Expected git repo version <= [1-9]" err
+'
+
+test_expect_failure 'ignore .git/ with invalid repository version' '
+	test_with_config "[core]repositoryformatversion = invalid"
+'
+
+
+test_expect_failure 'ignore .git/ with invalid config' '
+	test_with_config "["
+'
+
+test_done
diff --git a/t/t7006-pager.sh b/t/t7006-pager.sh
index c8dc665f2f..4f3794d415 100755
--- a/t/t7006-pager.sh
+++ b/t/t7006-pager.sh
@@ -360,27 +360,37 @@ test_pager_choices                       'git aliasedlog'
 test_default_pager        expect_success 'git -p aliasedlog'
 test_PAGER_overrides      expect_success 'git -p aliasedlog'
 test_core_pager_overrides expect_success 'git -p aliasedlog'
-test_core_pager_subdir    expect_failure 'git -p aliasedlog'
+test_core_pager_subdir    expect_success 'git -p aliasedlog'
 test_GIT_PAGER_overrides  expect_success 'git -p aliasedlog'
 
 test_default_pager        expect_success 'git -p true'
 test_PAGER_overrides      expect_success 'git -p true'
 test_core_pager_overrides expect_success 'git -p true'
-test_core_pager_subdir    expect_failure 'git -p true'
+test_core_pager_subdir    expect_success 'git -p true'
 test_GIT_PAGER_overrides  expect_success 'git -p true'
 
 test_default_pager        expect_success test_must_fail 'git -p request-pull'
 test_PAGER_overrides      expect_success test_must_fail 'git -p request-pull'
 test_core_pager_overrides expect_success test_must_fail 'git -p request-pull'
-test_core_pager_subdir    expect_failure test_must_fail 'git -p request-pull'
+test_core_pager_subdir    expect_success test_must_fail 'git -p request-pull'
 test_GIT_PAGER_overrides  expect_success test_must_fail 'git -p request-pull'
 
 test_default_pager        expect_success test_must_fail 'git -p'
 test_PAGER_overrides      expect_success test_must_fail 'git -p'
 test_local_config_ignored expect_failure test_must_fail 'git -p'
-test_no_local_config_subdir expect_success test_must_fail 'git -p'
 test_GIT_PAGER_overrides  expect_success test_must_fail 'git -p'
 
+test_expect_success TTY 'core.pager in repo config works and retains cwd' '
+	sane_unset GIT_PAGER &&
+	test_config core.pager "cat >cwd-retained" &&
+	(
+		cd sub &&
+		rm -f cwd-retained &&
+		test_terminal git -p rev-parse HEAD &&
+		test_path_is_file cwd-retained
+	)
+'
+
 test_doesnt_paginate      expect_failure test_must_fail 'git -p nonsense'
 
 test_pager_choices                       'git shortlog'