[PATCH] setup: only die on invalid .git under RUN_SETUP

[Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>]

Change RUN_SETUP_GENTLY to stop dying if e.g. the .git is "not a
repo". This means that we now recover in cases like:

    $ echo "gitdir: /foo/bar" > .git
    $ git ls-remote https://github.com/torvalds/linux
    [... ls-remote output ...]

But not (as intended):

    $ git rev-parse HEAD
    fatal: not a git repository: /foo/bar

The relevant setup_git_directory_gently_1() invocation was added in
01017dce546 (setup_git_directory_gently_1(): avoid die()ing,
2017-03-13), but I could reproduce this as far back as Git v1.8.0. I
don't know if this ever worked, but it should.

Let's also use the compiler to check enum arms for us, instead of
having a "default" fall-though case, this changes code added in
ce9b8aab5d9 (setup_git_directory_1(): avoid changing global state,
2017-03-13).

Reported-by: Tom Cook <tom.k.cook@xxxxxxxxx>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 setup.c            | 27 ++++++++++++++++++++++-----
 t/t0002-gitfile.sh |  8 ++++++--
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/setup.c b/setup.c
index eb9367ca5c..6ff145d58b 100644
--- a/setup.c
+++ b/setup.c
@@ -1033,7 +1033,8 @@ enum discovery_result {
 	/* these are errors */
 	GIT_DIR_HIT_CEILING = -1,
 	GIT_DIR_HIT_MOUNT_POINT = -2,
-	GIT_DIR_INVALID_GITFILE = -3
+	GIT_DIR_INVALID_GITFILE = -3,
+	GIT_DIR_GITFILE_NOT_A_REPO = -4,
 };
 
 /*
@@ -1118,8 +1119,11 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 				/* 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)
+			} else if (error_code == READ_GITFILE_ERR_NOT_A_REPO) {
+				return GIT_DIR_GITFILE_NOT_A_REPO;
+			} else if (error_code != READ_GITFILE_ERR_STAT_FAILED) {
 				return GIT_DIR_INVALID_GITFILE;
+			}
 		}
 		strbuf_setlen(dir, offset);
 		if (gitdirenv) {
@@ -1209,6 +1213,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	struct strbuf dir = STRBUF_INIT, gitdir = STRBUF_INIT;
 	const char *prefix = NULL;
 	struct repository_format repo_fmt = REPOSITORY_FORMAT_INIT;
+	int die_on_error = !nongit_ok;
+	enum discovery_result discovery;
 
 	/*
 	 * We may have read an incomplete configuration before
@@ -1231,7 +1237,9 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		die_errno(_("Unable to read current working directory"));
 	strbuf_addbuf(&dir, &cwd);
 
-	switch (setup_git_directory_gently_1(&dir, &gitdir, 1)) {
+	discovery = setup_git_directory_gently_1(&dir, &gitdir, die_on_error);
+
+	switch (discovery) {
 	case GIT_DIR_EXPLICIT:
 		prefix = setup_explicit_git_dir(gitdir.buf, &cwd, &repo_fmt, nongit_ok);
 		break;
@@ -1259,6 +1267,16 @@ const char *setup_git_directory_gently(int *nongit_ok)
 			    dir.buf);
 		*nongit_ok = 1;
 		break;
+	case GIT_DIR_GITFILE_NOT_A_REPO:
+		if (!nongit_ok)
+			die(_("not a git repository: %s"), dir.buf);
+		*nongit_ok = 1;
+		break;
+	case GIT_DIR_INVALID_GITFILE:
+		if (!nongit_ok)
+			die(_("invalid .git file: %s"), dir.buf);
+		*nongit_ok = 1;
+		break;
 	case GIT_DIR_NONE:
 		/*
 		 * As a safeguard against setup_git_directory_gently_1 returning
@@ -1266,8 +1284,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		 * set startup_info->have_repository to 1 when we did nothing to
 		 * find a repository.
 		 */
-	default:
-		BUG("unhandled setup_git_directory_1() result");
+		BUG("setup_git_directory_1() should not return GIT_DIR_NONE");
 	}
 
 	/*
diff --git a/t/t0002-gitfile.sh b/t/t0002-gitfile.sh
index 8440e6add1..176dc8c9dc 100755
--- a/t/t0002-gitfile.sh
+++ b/t/t0002-gitfile.sh
@@ -21,13 +21,17 @@ test_expect_success 'initial setup' '
 test_expect_success 'bad setup: invalid .git file format' '
 	echo "gitdir $REAL" >.git &&
 	test_must_fail git rev-parse 2>.err &&
-	test_i18ngrep "invalid gitfile format" .err
+	test_i18ngrep "invalid gitfile format" .err &&
+
+	git ls-remote "file://$REAL"
 '
 
 test_expect_success 'bad setup: invalid .git file path' '
 	echo "gitdir: $REAL.not" >.git &&
 	test_must_fail git rev-parse 2>.err &&
-	test_i18ngrep "not a git repository" .err
+	test_i18ngrep "not a git repository" .err &&
+
+	git ls-remote "file://$REAL"
 '
 
 test_expect_success 'final setup + check rev-parse --git-dir' '
-- 
2.32.0.954.g5a3a1483ade