[PATCH v3] builtin/push: call set_refspecs after validating remote

[Karthik Nayak <karthik.188@gmail.com>]

When an end-user runs "git push" with an empty string for the remote
repository name, e.g.

    $ git push '' main

"git push" fails with a BUG(). Even though this is a nonsense request
that we want to fail, we shouldn't hit a BUG().  Instead we want to give
a sensible error message, e.g., 'bad repository'".

This is because since 9badf97c42 (remote: allow resetting url list,
2024-06-14), we reset the remote URL if the provided URL is empty. When
a user of 'remotes_remote_get' tries to fetch a remote with an empty
repo name, the function initializes the remote via 'make_remote'. But
the remote is still not a valid remote, since the URL is empty, so it
tries to add the URL alias using 'add_url_alias'. This in-turn will call
'add_url', but since the URL is empty we call 'strvec_clear' on the
`remote->url`. Back in 'remotes_remote_get', we again check if the
remote is valid, which fails, so we return 'NULL' for the 'struct
remote *' value.

The 'builtin/push.c' code, calls 'set_refspecs' before validating the
remote. This worked with empty repo names earlier since we would get a
remote, albeit with an empty URL. With the new changes, we get a 'NULL'
remote value, this causes the check for remote to fail and raises the
BUG in 'set_refspecs'.

Do a simple fix by doing remote validation first. Also add a test to
validate the bug fix. With this, we can also now directly pass remote to
'set_refspecs' instead of it trying to lazily obtain it.

Helped-by: Jeff King <peff@peff.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---

Changes from v2:
- Updated the commit message to talk more about the user
experience at the start.
- Added another test to also check targeted refspec.

Range-diff against v2:
1:  fd9a9387e9 ! 1:  845be99dd6 builtin/push: call set_refspecs after validating remote
    @@ Metadata
      ## Commit message ##
         builtin/push: call set_refspecs after validating remote
     
    -    Since 9badf97c42 (remote: allow resetting url list, 2024-06-14), we
    -    reset the remote URL if the provided URL is empty. When a user of
    -    'remotes_remote_get' tries to fetch a remote with an empty repo name,
    -    the function initializes the remote via 'make_remote'. But the remote is
    -    still not a valid remote, since the URL is empty, so it tries to add the
    -    URL alias using 'add_url_alias'. This in-turn will call 'add_url', but
    -    since the URL is empty we call 'strvec_clear' on the `remote->url`. Back
    -    in 'remotes_remote_get', we again check if the remote is valid, which
    -    fails, so we return 'NULL' for the 'struct remote *' value
    +    When an end-user runs "git push" with an empty string for the remote
    +    repository name, e.g.
    +
    +        $ git push '' main
    +
    +    "git push" fails with a BUG(). Even though this is a nonsense request
    +    that we want to fail, we shouldn't hit a BUG().  Instead we want to give
    +    a sensible error message, e.g., 'bad repository'".
    +
    +    This is because since 9badf97c42 (remote: allow resetting url list,
    +    2024-06-14), we reset the remote URL if the provided URL is empty. When
    +    a user of 'remotes_remote_get' tries to fetch a remote with an empty
    +    repo name, the function initializes the remote via 'make_remote'. But
    +    the remote is still not a valid remote, since the URL is empty, so it
    +    tries to add the URL alias using 'add_url_alias'. This in-turn will call
    +    'add_url', but since the URL is empty we call 'strvec_clear' on the
    +    `remote->url`. Back in 'remotes_remote_get', we again check if the
    +    remote is valid, which fails, so we return 'NULL' for the 'struct
    +    remote *' value.
     
         The 'builtin/push.c' code, calls 'set_refspecs' before validating the
         remote. This worked with empty repo names earlier since we would get a
    @@ Commit message
         'set_refspecs' instead of it trying to lazily obtain it.
     
         Helped-by: Jeff King <peff@peff.net>
    +    Helped-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
     
      ## builtin/push.c ##
    @@ t/t5529-push-errors.sh: test_expect_success 'detect missing sha1 expressions ear
      	test_cmp expect rp-ran
      '
      
    -+# We need to use an existing local_ref so that the remote is mapped to
    -+# it in 'builtin/push.c:set_refspecs()'.
    -+test_expect_success 'detect empty remote' '
    ++# We use an existing local_ref, since it follows a different flow in
    ++# 'builtin/push.c:set_refspecs()' and we want to test that regression.
    ++test_expect_success 'detect empty remote with existing local ref' '
     +	test_must_fail git push "" main 2> stderr &&
     +	grep "fatal: bad repository ${SQ}${SQ}" stderr
     +'
    ++
    ++# While similar to the previous test, here we want to ensure that
    ++# even targeted refspecs are handled.
    ++test_expect_success 'detect empty remote with targeted refspec' '
    ++	test_must_fail git push "" HEAD:refs/heads/main 2> stderr &&
    ++	grep "fatal: bad repository ${SQ}${SQ}" stderr
    ++'
     +
      test_expect_success 'detect ambiguous refs early' '
      	git branch foo &&

 builtin/push.c         | 21 +++++++--------------
 t/t5529-push-errors.sh | 17 +++++++++++++++++
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/builtin/push.c b/builtin/push.c
index 8260c6e46a..7a67398124 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -96,9 +96,8 @@ static void refspec_append_mapped(struct refspec *refspec, const char *ref,
 	refspec_append(refspec, ref);
 }
 
-static void set_refspecs(const char **refs, int nr, const char *repo)
+static void set_refspecs(const char **refs, int nr, struct remote *remote)
 {
-	struct remote *remote = NULL;
 	struct ref *local_refs = NULL;
 	int i;
 
@@ -124,17 +123,10 @@ static void set_refspecs(const char **refs, int nr, const char *repo)
 				local_refs = get_local_heads();
 
 			/* Does "ref" uniquely name our ref? */
-			if (count_refspec_match(ref, local_refs, &matched) != 1) {
+			if (count_refspec_match(ref, local_refs, &matched) != 1)
 				refspec_append(&rs, ref);
-			} else {
-				/* lazily grab remote */
-				if (!remote)
-					remote = remote_get(repo);
-				if (!remote)
-					BUG("must get a remote for repo '%s'", repo);
-
+			else
 				refspec_append_mapped(&rs, ref, remote, matched);
-			}
 		} else
 			refspec_append(&rs, ref);
 	}
@@ -630,10 +622,8 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	if (tags)
 		refspec_append(&rs, "refs/tags/*");
 
-	if (argc > 0) {
+	if (argc > 0)
 		repo = argv[0];
-		set_refspecs(argv + 1, argc - 1, repo);
-	}
 
 	remote = pushremote_get(repo);
 	if (!remote) {
@@ -649,6 +639,9 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 		    "    git push <name>\n"));
 	}
 
+	if (argc > 0)
+		set_refspecs(argv + 1, argc - 1, remote);
+
 	if (remote->mirror)
 		flags |= (TRANSPORT_PUSH_MIRROR|TRANSPORT_PUSH_FORCE);
 
diff --git a/t/t5529-push-errors.sh b/t/t5529-push-errors.sh
index 0247137cb3..17d7257892 100755
--- a/t/t5529-push-errors.sh
+++ b/t/t5529-push-errors.sh
@@ -2,6 +2,9 @@
 
 test_description='detect some push errors early (before contacting remote)'
 
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
 TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
@@ -38,6 +41,20 @@ test_expect_success 'detect missing sha1 expressions early' '
 	test_cmp expect rp-ran
 '
 
+# We use an existing local_ref, since it follows a different flow in
+# 'builtin/push.c:set_refspecs()' and we want to test that regression.
+test_expect_success 'detect empty remote with existing local ref' '
+	test_must_fail git push "" main 2> stderr &&
+	grep "fatal: bad repository ${SQ}${SQ}" stderr
+'
+
+# While similar to the previous test, here we want to ensure that
+# even targeted refspecs are handled.
+test_expect_success 'detect empty remote with targeted refspec' '
+	test_must_fail git push "" HEAD:refs/heads/main 2> stderr &&
+	grep "fatal: bad repository ${SQ}${SQ}" stderr
+'
+
 test_expect_success 'detect ambiguous refs early' '
 	git branch foo &&
 	git tag foo &&
-- 
2.45.2