[PATCH] submodule_init: die cleanly on submodules without url defined

[Jeff King]

When we init a submodule, we try to die when it has no URL
defined:

  url = xstrdup(sub->url);
  if (!url)
          die(...);

But that's clearly nonsense. xstrdup() will never return
NULL, and if sub->url is NULL, we'll segfault.

These two bits of code need to be flipped, so we check
sub->url before looking at it.

Signed-off-by: Jeff King <p...@peff.net>
---
The bug is from the original submodule--helper, so it first appeared in
v2.9.x.

 builtin/submodule--helper.c | 6 +++---
 t/t7400-submodule-basic.sh  | 8 ++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 36e423182..566a5b6a6 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -376,12 +376,12 @@ static void init_submodule(const char *path, const char 
*prefix, int quiet)
        strbuf_reset(&sb);
        strbuf_addf(&sb, "submodule.%s.url", sub->name);
        if (git_config_get_string(sb.buf, &url)) {
-               url = xstrdup(sub->url);
-
-               if (!url)
+               if (!sub->url)
                        die(_("No url found for submodule path '%s' in 
.gitmodules"),
                                displaypath);
 
+               url = xstrdup(sub->url);
+
                /* Possibly a url relative to parent */
                if (starts_with_dot_dot_slash(url) ||
                    starts_with_dot_slash(url)) {
diff --git a/t/t7400-submodule-basic.sh b/t/t7400-submodule-basic.sh
index c2706fe47..1b8f1dbd3 100755
--- a/t/t7400-submodule-basic.sh
+++ b/t/t7400-submodule-basic.sh
@@ -38,6 +38,14 @@ test_expect_success 'submodule update aborts on missing 
.gitmodules file' '
        test_i18ngrep "Submodule path .sub. not initialized" actual
 '
 
+test_expect_success 'submodule update aborts on missing gitmodules url' '
+       test_when_finished "git update-index --remove sub" &&
+       git update-index --add --cacheinfo 160000,$(git rev-parse HEAD),sub &&
+       test_when_finished "rm -f .gitmodules" &&
+       git config -f .gitmodules submodule.s.path sub &&
+       test_must_fail git submodule init
+'
+
 test_expect_success 'configuration parsing' '
        test_when_finished "rm -f .gitmodules" &&
        cat >.gitmodules <<-\EOF &&
-- 
2.13.0.rc0.459.g06dc2b676