[PATCH 38/43] Allow to undo setup_git_directory_gently() gracefully (and fix alias code)

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

unset_git_directory() can only clean up things as long as
set_git_dir() has not been called because set_git_dir() sets internal
state itself. Even worse, set_git_dir() may override $GIT_DIR env
variable.

Add unset_git_env() to undo set_git_dir(), allow unset_git_directory()
to undo a succesful setup_git_directory_gently().

While at there, fix alias handling code regarding git_dir {,un-}setup,
use unset_git_directory() instead of just chdir() back.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 cache.h       |    1 +
 environment.c |   20 ++++++++++++++++++++
 git.c         |   11 +++++------
 setup.c       |    2 ++
 4 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/cache.h b/cache.h
index bdcd1ec..137edac 100644
--- a/cache.h
+++ b/cache.h
@@ -422,6 +422,7 @@ extern void setup_work_tree(void);
 extern const char *setup_git_directory_gently(int *);
 extern const char *setup_git_directory(void);
 extern void unset_git_directory(const char *prefix);
+extern void unset_git_env();
 extern const char *prefix_path(const char *prefix, int len, const char *path);
 extern const char *prefix_filename(const char *prefix, int len, const char *path);
 extern int check_filename(const char *prefix, const char *name);
diff --git a/environment.c b/environment.c
index c36c902..6127025 100644
--- a/environment.c
+++ b/environment.c
@@ -62,6 +62,7 @@ char *git_work_tree_cfg;
 static char *work_tree;
 
 static const char *git_dir;
+static const char *original_git_dir;
 static char *git_object_dir, *git_index_file, *git_refs_dir, *git_graft_file;
 
 /*
@@ -81,6 +82,20 @@ const char * const local_repo_env[LOCAL_REPO_ENV_SIZE + 1] = {
 	NULL
 };
 
+void unset_git_env(void)
+{
+	git_dir = NULL;
+	if (original_git_dir)
+		setenv(GIT_DIR_ENVIRONMENT, original_git_dir, 1);
+	else
+		unsetenv(GIT_DIR_ENVIRONMENT);
+	git_object_dir = NULL;
+	git_refs_dir = NULL;
+	git_index_file = NULL;
+	git_graft_file = NULL;
+	read_replace_refs = 1;
+}
+
 static void setup_git_env(void)
 {
 	git_dir = getenv(GIT_DIR_ENVIRONMENT);
@@ -184,6 +199,11 @@ char *get_graft_file(void)
 
 int set_git_dir(const char *path)
 {
+	static int original_git_dir_set = 0;
+	if (!original_git_dir_set) {
+		original_git_dir = getenv(GIT_DIR_ENVIRONMENT);
+		original_git_dir_set = 1;
+	}
 	if (setenv(GIT_DIR_ENVIRONMENT, path, 1))
 		return error("Could not set GIT_DIR to '%s'", path);
 	setup_git_env();
diff --git a/git.c b/git.c
index d60f792..17482dd 100644
--- a/git.c
+++ b/git.c
@@ -146,14 +146,13 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 static int handle_alias(int *argcp, const char ***argv)
 {
 	int envchanged = 0, ret = 0, saved_errno = errno;
-	const char *subdir;
 	int count, option_count;
 	const char **new_argv;
 	const char *alias_command;
 	char *alias_string;
 	int unused_nongit;
 
-	subdir = setup_git_directory_gently(&unused_nongit);
+	setup_git_directory_gently(&unused_nongit);
 
 	alias_command = (*argv)[0];
 	alias_string = alias_lookup(alias_command);
@@ -210,8 +209,7 @@ static int handle_alias(int *argcp, const char ***argv)
 		ret = 1;
 	}
 
-	if (subdir && chdir(subdir))
-		die_errno("Cannot change to '%s'", subdir);
+	unset_git_directory(startup_info->prefix);
 
 	errno = saved_errno;
 
@@ -240,8 +238,6 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv)
 	int status;
 	struct stat st;
 
-	memset(&git_startup_info, 0, sizeof(git_startup_info));
-	startup_info = &git_startup_info;
 	startup_info->help = argc == 2 && !strcmp(argv[1], "-h");
 	if (!startup_info->help) {
 		if (p->option & RUN_SETUP)
@@ -486,6 +482,9 @@ int main(int argc, const char **argv)
 {
 	const char *cmd;
 
+	memset(&git_startup_info, 0, sizeof(git_startup_info));
+	startup_info = &git_startup_info;
+
 	cmd = git_extract_argv0_path(argv[0]);
 	if (!cmd)
 		cmd = "git-help";
diff --git a/setup.c b/setup.c
index 858cf6b..b0269aa 100644
--- a/setup.c
+++ b/setup.c
@@ -336,6 +336,8 @@ void unset_git_directory(const char *prefix)
 		die("Cannot change to '%s'", prefix);
 
 	if (startup_info) {
+		if (startup_info->have_repository)
+			unset_git_env();
 		startup_info->prefix = NULL;
 		startup_info->have_repository = 0;
 	}
-- 
1.7.0.rc1.541.g2da82.dirty