Suggest the intended form when a remote/branch slip is given

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/branch.c

@@ -957,6 +957,23 @@ int cmd_branch(int argc,
 		if (!refs_ref_exists(get_main_ref_store(the_repository), branch->refname)) {
 			if (!argc || branch_checked_out(branch->refname))
 				die(_("no commit on branch '%s' yet"), branch->name);
+			if (argc == 1 && !strchr(new_upstream, '/') &&
+			    remote_is_configured(remote_get(new_upstream), 0)) {
+				struct strbuf remote_ref = STRBUF_INIT;
+
+				strbuf_addf(&remote_ref, "refs/remotes/%s/%s",
+					    new_upstream, argv[0]);
+				if (refs_ref_exists(get_main_ref_store(the_repository),
+						    remote_ref.buf)) {
+					int code = die_message(_("--set-upstream-to takes a single <remote>/<branch> argument"));
+					advise_if_enabled(ADVICE_SET_UPSTREAM_FAILURE,
+							  _("Did you mean to use: git branch --set-upstream-to=%s/%s?"),
+							  new_upstream, argv[0]);
+					strbuf_release(&remote_ref);
+					exit(code);
+				}
+				strbuf_release(&remote_ref);
+			}
 			die(_("branch '%s' does not exist"), branch->name);
 		}
 

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"
@@ -744,6 +745,29 @@ int cmd_push(int argc,
 
 	if (repo) {
 		if (!add_remote_or_group(repo, &remote_group)) {
+			const char *slash = strchr(repo, '/');
+			struct remote *r;
+
+			/*
+			 * A "<remote>/<branch>" argument that does not name
+			 * a path is likely a slip for the separate
+			 * "<remote> <branch>" form, so suggest that instead.
+			 */
+			if (slash && slash[1] && !file_exists(repo)) {
+				struct strbuf name = STRBUF_INIT;
+
+				strbuf_add(&name, repo, slash - repo);
+				if (remote_is_configured(remote_get(name.buf), 0)) {
+					int 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);
+				}
+				strbuf_release(&name);
+			}
+
 			/*
 			 * Not a configured remote name or group name.
 			 * Try treating it as a direct URL or path, e.g.
@@ -753,7 +777,7 @@ 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/t3200-branch.sh

@@ -1022,6 +1022,44 @@ test_expect_success '--set-upstream-to fails on a missing dst branch' '
 	test_cmp expect err
 '
 
+test_expect_success '--set-upstream-to suggests <remote>/<branch> on slip' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	git update-ref refs/remotes/slip-remote/slip-feature HEAD &&
+	test_must_fail git branch --set-upstream-to slip-remote slip-feature 2>err &&
+	test_grep "takes a single <remote>/<branch> argument" err &&
+	test_grep "hint: Did you mean to use: git branch --set-upstream-to=slip-remote/slip-feature?" err &&
+	test_must_fail git -c advice.setUpstreamFailure=false \
+		branch --set-upstream-to slip-remote slip-feature 2>err &&
+	test_grep ! "Did you mean" err
+'
+
+test_expect_success '--set-upstream-to does not suggest when no matching remote ref' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	test_must_fail git branch --set-upstream-to slip-remote no-such-branch 2>err &&
+	test_grep "branch ${SQ}no-such-branch${SQ} does not exist" err &&
+	test_grep ! "Did you mean" err
+'
+
+test_expect_success '--set-upstream-to to a local branch is not mistaken for a slip' '
+	git branch slip-local-upstream &&
+	git branch slip-local-target &&
+	git branch --set-upstream-to=slip-local-upstream slip-local-target 2>err &&
+	test_grep ! "Did you mean" err &&
+	echo refs/heads/slip-local-upstream >expect &&
+	git config branch.slip-local-target.merge >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--set-upstream-to slip suggestion keeps a slashed branch name' '
+	test_when_finished "git remote remove slip-remote" &&
+	git remote add slip-remote . &&
+	git update-ref refs/remotes/slip-remote/slip/feature HEAD &&
+	test_must_fail git branch --set-upstream-to slip-remote slip/feature 2>err &&
+	test_grep "hint: Did you mean to use: git branch --set-upstream-to=slip-remote/slip/feature?" err
+'
+
 test_expect_success '--set-upstream-to fails on a missing src branch' '
 	test_must_fail git branch --set-upstream-to does-not-exist main 2>err &&
 	test_grep "the requested upstream branch '"'"'does-not-exist'"'"' does not exist" err

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 &&