push: disallow --all and refspecs when remote.<name>.mirror is set

Pushes with --all, or refspecs are disallowed when --mirror is given
to 'git push', or when 'remote.<name>.mirror' is set in the config of
the repository, because they can have surprising
effects. 800a4ab399 ("push: check for errors earlier", 2018-05-16)
refactored this code to do that check earlier, so we can explicitly
check for the presence of flags, instead of their sideeffects.

However when 'remote.<name>.mirror' is set in the config, the
TRANSPORT_PUSH_MIRROR flag would only be set after we calling
'do_push()', so the checks would miss it entirely.

This leads to surprises for users [*1*].

Fix this by making sure we set the flag (if appropriate) before
checking for compatibility of the various options.

*1*: https://twitter.com/FiloSottile/status/1163918701462249472

Reported-by: Filippo Valsorda <filippo@ml.filippo.io>
Helped-by: Saleem Rashid
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/push.c

diff --git a/builtin/push.c b/builtin/push.c
index 8bb8a08..5896bde 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -382,30 +382,14 @@ static int push_with_options(struct transport *transport, struct refspec *rs,
 }
 
 static int do_push(const char *repo, int flags,
-		   const struct string_list *push_options)
+		   const struct string_list *push_options,
+		   struct remote *remote)
 {
 	int i, errs;
-	struct remote *remote = pushremote_get(repo);
 	const char **url;
 	int url_nr;
 	struct refspec *push_refspec = &rs;
 
-	if (!remote) {
-		if (repo)
-			die(_("bad repository '%s'"), repo);
-		die(_("No configured push destination.\n"
-		    "Either specify the URL from the command-line or configure a remote repository using\n"
-		    "\n"
-		    "    git remote add <name> <url>\n"
-		    "\n"
-		    "and then push using the remote name\n"
-		    "\n"
-		    "    git push <name>\n"));
-	}
-
-	if (remote->mirror)
-		flags |= (TRANSPORT_PUSH_MIRROR|TRANSPORT_PUSH_FORCE);
-
 	if (push_options->nr)
 		flags |= TRANSPORT_PUSH_OPTIONS;
 
@@ -545,6 +529,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	struct string_list push_options_cmdline = STRING_LIST_INIT_DUP;
 	struct string_list *push_options;
 	const struct string_list_item *item;
+	struct remote *remote;
 
 	struct option options[] = {
 		OPT__VERBOSITY(&verbosity),
@@ -599,20 +584,6 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 		die(_("--delete is incompatible with --all, --mirror and --tags"));
 	if (deleterefs && argc < 2)
 		die(_("--delete doesn't make sense without any refs"));
-	if (flags & TRANSPORT_PUSH_ALL) {
-		if (tags)
-			die(_("--all and --tags are incompatible"));
-		if (argc >= 2)
-			die(_("--all can't be combined with refspecs"));
-	}
-	if (flags & TRANSPORT_PUSH_MIRROR) {
-		if (tags)
-			die(_("--mirror and --tags are incompatible"));
-		if (argc >= 2)
-			die(_("--mirror can't be combined with refspecs"));
-	}
-	if ((flags & TRANSPORT_PUSH_ALL) && (flags & TRANSPORT_PUSH_MIRROR))
-		die(_("--all and --mirror are incompatible"));
 
 	if (recurse_submodules == RECURSE_SUBMODULES_CHECK)
 		flags |= TRANSPORT_RECURSE_SUBMODULES_CHECK;
@@ -629,11 +600,43 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 		set_refspecs(argv + 1, argc - 1, repo);
 	}
 
+	remote = pushremote_get(repo);
+	if (!remote) {
+		if (repo)
+			die(_("bad repository '%s'"), repo);
+		die(_("No configured push destination.\n"
+		    "Either specify the URL from the command-line or configure a remote repository using\n"
+		    "\n"
+		    "    git remote add <name> <url>\n"
+		    "\n"
+		    "and then push using the remote name\n"
+		    "\n"
+		    "    git push <name>\n"));
+	}
+
+	if (remote->mirror)
+		flags |= (TRANSPORT_PUSH_MIRROR|TRANSPORT_PUSH_FORCE);
+
+	if (flags & TRANSPORT_PUSH_ALL) {
+		if (tags)
+			die(_("--all and --tags are incompatible"));
+		if (argc >= 2)
+			die(_("--all can't be combined with refspecs"));
+	}
+	if (flags & TRANSPORT_PUSH_MIRROR) {
+		if (tags)
+			die(_("--mirror and --tags are incompatible"));
+		if (argc >= 2)
+			die(_("--mirror can't be combined with refspecs"));
+	}
+	if ((flags & TRANSPORT_PUSH_ALL) && (flags & TRANSPORT_PUSH_MIRROR))
+		die(_("--all and --mirror are incompatible"));
+
 	for_each_string_list_item(item, push_options)
 		if (strchr(item->string, '\n'))
 			die(_("push options must not have new line characters"));
 
-	rc = do_push(repo, flags, push_options);
+	rc = do_push(repo, flags, push_options, remote);
 	string_list_clear(&push_options_cmdline, 0);
 	string_list_clear(&push_options_config, 0);
 	if (rc == -1)

t/t5517-push-mirror.sh

diff --git a/t/t5517-push-mirror.sh b/t/t5517-push-mirror.sh
index c05a661..e4edd56 100755
--- a/t/t5517-push-mirror.sh
+++ b/t/t5517-push-mirror.sh
@@ -265,4 +265,14 @@
 
 '
 
+test_expect_success 'push to mirrored repository with refspec fails' '
+	mk_repo_pair &&
+	(
+		cd master &&
+		echo one >foo && git add foo && git commit -m one &&
+		git config --add remote.up.mirror true &&
+		test_must_fail git push up master
+	)
+'
+
 test_done