sequencer: pass absolute GIT_DIR to exec commands

When we replaced the old shell script based interactive rebase in
commmit 18633e1a22 ("rebase -i: use the rebase--helper builtin",
2017-02-09) we introduced a regression of functionality in that the
GIT_DIR would be sent to the environment of the exec command as-is.

This generally meant that it would be passed as "GIT_DIR=.git", which
causes problems for any exec command that wants to run git commands in
a subdirectory.

This isn't a very large regression, since it is not that likely that the
exec command will run a git command, and even less likely that it will
need to do so in a subdir. This regression was discovered by a build
system which uses git-describe to find the current version of the build
system, and happened to do so from the src/ sub directory of the
project.

Fix this by passing in the absolute path of the git directory into the
child environment.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -1821,12 +1821,15 @@ static int error_failed_squash(struct commit *commit,
 
 static int do_exec(const char *command_line)
 {
+	struct argv_array child_env = ARGV_ARRAY_INIT;
 	const char *child_argv[] = { NULL, NULL };
 	int dirty, status;
 
 	fprintf(stderr, "Executing: %s\n", command_line);
 	child_argv[0] = command_line;
-	status = run_command_v_opt(child_argv, RUN_USING_SHELL);
+	argv_array_pushf(&child_env, "GIT_DIR=%s", absolute_path(get_git_dir()));
+	status = run_command_v_opt_cd_env(child_argv, RUN_USING_SHELL, NULL,
+					  child_env.argv);
 
 	/* force re-reading of the cache */
 	if (discard_cache() < 0 || read_cache() < 0)
@@ -1856,6 +1859,8 @@ static int do_exec(const char *command_line)
 		status = 1;
 	}
 
+	argv_array_clear(&child_env);
+
 	return status;
 }
 

t/t3404-rebase-interactive.sh

@@ -108,6 +108,17 @@ test_expect_success 'rebase -i with the exec command runs from tree root' '
 	rm -fr subdir
 '
 
+test_expect_success 'rebase -i with exec allows git commands in subdirs' '
+	test_when_finished "rm -rf subdir" &&
+	test_when_finished "git rebase --abort ||:" &&
+	git checkout master &&
+	mkdir subdir && (cd subdir &&
+	set_fake_editor &&
+	FAKE_LINES="1 exec_cd_subdir_&&_git_rev-parse_--is-inside-work-tree" \
+		git rebase -i HEAD^
+	)
+'
+
 test_expect_success 'rebase -i with the exec command checks tree cleanness' '
 	git checkout master &&
 	set_fake_editor &&