[PATCH v2 8/8] Use the early config machinery to expand aliases

[Johannes Schindelin <johannes.schindelin@gmx.de>]

We already taught alias_lookup() to use the early config if the .git/
directory was not yet discovered, of course, however, since we called
setup_git_directory_gently() before expanding the alias (if any), we
only used the early config code path only if outside of any Git-managed
directory.

With this commit, we finally switch over to really using the early
config code path.

Rather than just chdir()ing into the indicated directory in case of an
alias expanding to a shell command, we simply set up the .git/ directory
so that e.g. GIT_PREFIX is set as expected.

This change also fixes a known issue where Git tried to read the pager
config from an incorrect path in a subdirectory of a Git worktree if an
alias expanded to a shell command.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 git.c            | 59 +++++++-------------------------------------------------
 t/t7006-pager.sh |  2 +-
 2 files changed, 8 insertions(+), 53 deletions(-)

diff --git a/git.c b/git.c
index 4163beaead4..6511595d467 100644
--- a/git.c
+++ b/git.c
@@ -16,50 +16,6 @@ const char git_more_info_string[] =
 	   "to read about a specific subcommand or concept.");
 
 static int use_pager = -1;
-static char *orig_cwd;
-static const char *env_names[] = {
-	GIT_DIR_ENVIRONMENT,
-	GIT_WORK_TREE_ENVIRONMENT,
-	GIT_IMPLICIT_WORK_TREE_ENVIRONMENT,
-	GIT_PREFIX_ENVIRONMENT
-};
-static char *orig_env[4];
-static int save_restore_env_balance;
-
-static void save_env_before_alias(void)
-{
-	int i;
-
-	assert(save_restore_env_balance == 0);
-	save_restore_env_balance = 1;
-	orig_cwd = xgetcwd();
-	for (i = 0; i < ARRAY_SIZE(env_names); i++) {
-		orig_env[i] = getenv(env_names[i]);
-		orig_env[i] = xstrdup_or_null(orig_env[i]);
-	}
-}
-
-static void restore_env(int external_alias)
-{
-	int i;
-
-	assert(save_restore_env_balance == 1);
-	save_restore_env_balance = 0;
-	if (!external_alias && orig_cwd && chdir(orig_cwd))
-		die_errno("could not move to %s", orig_cwd);
-	free(orig_cwd);
-	for (i = 0; i < ARRAY_SIZE(env_names); i++) {
-		if (external_alias &&
-		    !strcmp(env_names[i], GIT_PREFIX_ENVIRONMENT))
-			continue;
-		if (orig_env[i]) {
-			setenv(env_names[i], orig_env[i], 1);
-			free(orig_env[i]);
-		} else {
-			unsetenv(env_names[i]);
-		}
-	}
-}
 
 static void commit_pager_choice(void) {
 	switch (use_pager) {
@@ -245,36 +201,37 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 
 static int handle_alias(int *argcp, const char ***argv)
 {
+	struct strbuf cdup_dir = STRBUF_INIT;
 	int envchanged = 0, ret = 0, saved_errno = errno;
 	int count, option_count;
 	const char **new_argv;
 	const char *alias_command;
 	char *alias_string;
-	int unused_nongit;
-
-	save_env_before_alias();
-	setup_git_directory_gently(&unused_nongit);
 
 	alias_command = (*argv)[0];
-	alias_string = alias_lookup(alias_command, NULL);
+	alias_string = alias_lookup(alias_command, &cdup_dir);
 	if (alias_string) {
 		if (alias_string[0] == '!') {
 			struct child_process child = CHILD_PROCESS_INIT;
 
+			if (cdup_dir.len)
+				setup_git_directory();
+
 			commit_pager_choice();
-			restore_env(1);
 
 			child.use_shell = 1;
 			argv_array_push(&child.args, alias_string + 1);
 			argv_array_pushv(&child.args, (*argv) + 1);
 
 			ret = run_command(&child);
+			strbuf_release(&cdup_dir);
 			if (ret >= 0)   /* normal exit */
 				exit(ret);
 
 			die_errno("While expanding alias '%s': '%s'",
 			    alias_command, alias_string + 1);
 		}
+		strbuf_release(&cdup_dir);
 		count = split_cmdline(alias_string, &new_argv);
 		if (count < 0)
 			die("Bad alias.%s string: %s", alias_command,
@@ -308,8 +265,6 @@ static int handle_alias(int *argcp, const char ***argv)
 		ret = 1;
 	}
 
-	restore_env(0);
-
 	errno = saved_errno;
 
 	return ret;
diff --git a/t/t7006-pager.sh b/t/t7006-pager.sh
index 83881ec3a0c..20b4d83c281 100755
--- a/t/t7006-pager.sh
+++ b/t/t7006-pager.sh
@@ -391,7 +391,7 @@ test_expect_success TTY 'core.pager in repo config works and retains cwd' '
 	)
 '
 
-test_expect_failure TTY 'core.pager is found via alias in subdirectory' '
+test_expect_success TTY 'core.pager is found via alias in subdirectory' '
 	sane_unset GIT_PAGER &&
 	test_config core.pager "cat >via-alias" &&
 	(
-- 
2.13.0.windows.1.460.g13f583bedb5