push: suggest <remote> <branch> for a slash slip

When pushing the 'main' branch to the remote 'origin', i.e.,

    $ git push origin main

it is easy to mistakenly write

    $ git push origin/main

That is parsed as the repository to push to, and since 'origin/main'
is neither a configured remote nor a path it dies with:

    fatal: 'origin/main' does not appear to be a git repository

Often 'origin/main' does not exist as a repository, so the command
fails without doing any harm, but it gives no hint that a space was
meant instead of a slash and can leave the user puzzled.

When the argument is not an existing path or configured remote but
its part before the first slash names one, suggest the intended
'<remote> <branch>' form:

    $ git push origin main

The suggestion is shown as advice so it can be silenced with
advice.pushRepoLooksLikeRef.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/advice.adoc

@@ -90,6 +90,11 @@ all advice messages.
 		Shown when linkgit:git-push[1] rejects a forced update of
 		a branch when its remote-tracking ref has updates that we
 		do not have locally.
+	pushRepoLooksLikeRef::
+		Shown when the repository given to linkgit:git-push[1] is not
+		a configured remote but looks like a `<remote>/<branch>` ref,
+		suggesting that the remote and branch be given as separate
+		arguments.
 	pushUnqualifiedRefname::
 		Shown when linkgit:git-push[1] gives up trying to
 		guess based on the source and destination refs what

advice.c

@@ -69,6 +69,7 @@ static struct {
 	[ADVICE_PUSH_NON_FF_CURRENT]			= { "pushNonFFCurrent" },
 	[ADVICE_PUSH_NON_FF_MATCHING]			= { "pushNonFFMatching" },
 	[ADVICE_PUSH_REF_NEEDS_UPDATE]			= { "pushRefNeedsUpdate" },
+	[ADVICE_PUSH_REPO_LOOKS_LIKE_REF]		= { "pushRepoLooksLikeRef" },
 	[ADVICE_PUSH_UNQUALIFIED_REF_NAME]		= { "pushUnqualifiedRefName" },
 	[ADVICE_PUSH_UPDATE_REJECTED]			= { "pushUpdateRejected" },
 	[ADVICE_PUSH_UPDATE_REJECTED_ALIAS]		= { "pushNonFastForward" }, /* backwards compatibility */

advice.h

@@ -36,6 +36,7 @@ enum advice_type {
 	ADVICE_PUSH_NON_FF_CURRENT,
 	ADVICE_PUSH_NON_FF_MATCHING,
 	ADVICE_PUSH_REF_NEEDS_UPDATE,
+	ADVICE_PUSH_REPO_LOOKS_LIKE_REF,
 	ADVICE_PUSH_UNQUALIFIED_REF_NAME,
 	ADVICE_PUSH_UPDATE_REJECTED,
 	ADVICE_PUSH_UPDATE_REJECTED_ALIAS,

builtin/push.c

@@ -8,6 +8,7 @@
 #include "advice.h"
 #include "branch.h"
 #include "config.h"
+#include "dir.h"
 #include "environment.h"
 #include "gettext.h"
 #include "hex.h"
@@ -662,6 +663,29 @@ static int push_multiple(struct string_list *list,
 	return result;
 }
 
+static void die_if_repo_looks_like_ref(const char *repo)
+{
+	const char *slash = strchr(repo, '/');
+	struct strbuf name = STRBUF_INIT;
+	int code;
+
+	if (!slash || !slash[1] || file_exists(repo))
+		return;
+
+	strbuf_add(&name, repo, slash - repo);
+	if (!remote_is_configured(remote_get(name.buf), 0)) {
+		strbuf_release(&name);
+		return;
+	}
+
+	code = die_message(_("'%s' is not a valid push target"), repo);
+	advise_if_enabled(ADVICE_PUSH_REPO_LOOKS_LIKE_REF,
+			  _("Did you mean to use: git push %s %s?"),
+			  name.buf, slash + 1);
+	strbuf_release(&name);
+	exit(code);
+}
+
 int cmd_push(int argc,
 	     const char **argv,
 	     const char *prefix,
@@ -744,6 +768,11 @@ int cmd_push(int argc,
 
 	if (repo) {
 		if (!add_remote_or_group(repo, &remote_group)) {
+			struct remote *r;
+
+			if (advice_enabled(ADVICE_PUSH_REPO_LOOKS_LIKE_REF))
+				die_if_repo_looks_like_ref(repo);
+
 			/*
 			 * Not a configured remote name or group name.
 			 * Try treating it as a direct URL or path, e.g.
@@ -753,7 +782,7 @@ int cmd_push(int argc,
 			 * from the URL so the loop below can handle it
 			 * identically to a named remote.
 			 */
-			struct remote *r = pushremote_get(repo);
+			r = pushremote_get(repo);
 			if (!r)
 				die(_("bad repository '%s'"), repo);
 			string_list_append(&remote_group, r->name);

t/t5529-push-errors.sh

@@ -54,6 +54,37 @@ test_expect_success 'detect empty remote with targeted refspec' '
 	grep "fatal: bad repository ${SQ}${SQ}" stderr
 '
 
+test_expect_success 'suggest <remote> <branch> for a <remote>/<branch> slip' '
+	test_must_fail git push origin/main 2>stderr &&
+	grep "${SQ}origin/main${SQ} is not a valid push target" stderr &&
+	grep "hint: Did you mean to use: git push origin main?" stderr &&
+	test_must_fail git -c advice.pushRepoLooksLikeRef=false push origin/main 2>stderr &&
+	! grep "Did you mean" stderr
+'
+
+test_expect_success 'suggest <remote> <branch> when the branch has slashes' '
+	test_must_fail git push origin/feature/x 2>stderr &&
+	grep "hint: Did you mean to use: git push origin feature/x?" stderr
+'
+
+test_expect_success 'no suggestion when prefix is not a configured remote' '
+	test_must_fail git push not-a-remote/main 2>stderr &&
+	! grep "Did you mean" stderr
+'
+
+test_expect_success 'no suggestion for a trailing slash with no branch' '
+	test_must_fail git push origin/ 2>stderr &&
+	! grep "Did you mean" stderr
+'
+
+test_expect_success 'no suggestion when the argument is an existing path' '
+	test_when_finished "rm -rf origin" &&
+	git init --bare origin/main &&
+	git push origin/main HEAD:refs/heads/pushed 2>stderr &&
+	! grep "Did you mean" stderr &&
+	git -C origin/main rev-parse --verify refs/heads/pushed
+'
+
 test_expect_success 'detect ambiguous refs early' '
 	git branch foo &&
 	git tag foo &&