branch -m: update all per-worktree HEADs

When renaming a branch, currently only the HEAD of current working tree
is updated, but it must update HEADs of all working trees which point at
the old branch.

This is the current behavior, /path/to/wt's HEAD is not updated:

  % git worktree list
  /path/to     2c3c5f2 [master]
  /path/to/wt  2c3c5f2 [oldname]
  % git branch -m master master2
  % git worktree list
  /path/to     2c3c5f2 [master2]
  /path/to/wt  2c3c5f2 [oldname]
  % git branch -m oldname newname
  % git worktree list
  /path/to     2c3c5f2 [master2]
  /path/to/wt  0000000 [oldname]

This patch fixes this issue by updating all relevant worktree HEADs
when renaming a branch.

Signed-off-by: Kazuki Yamaguchi <k@rhe.jp>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -344,3 +344,26 @@ void die_if_checked_out(const char *branch)
 		die(_("'%s' is already checked out at '%s'"), branch, existing);
 	}
 }
+
+int replace_each_worktree_head_symref(const char *oldref, const char *newref)
+{
+	int ret = 0;
+	struct worktree **worktrees = get_worktrees();
+	int i;
+
+	for (i = 0; worktrees[i]; i++) {
+		if (worktrees[i]->is_detached)
+			continue;
+		if (strcmp(oldref, worktrees[i]->head_ref))
+			continue;
+
+		if (set_worktree_head_symref(worktrees[i]->git_dir, newref)) {
+			ret = -1;
+			error(_("HEAD of working tree %s is not updated"),
+			      worktrees[i]->path);
+		}
+	}
+
+	free_worktrees(worktrees);
+	return ret;
+}

branch.h

@@ -60,4 +60,11 @@ extern int read_branch_desc(struct strbuf *, const char *branch_name);
  */
 extern void die_if_checked_out(const char *branch);
 
+/*
+ * Update all per-worktree HEADs pointing at the old ref to point the new ref.
+ * This will be used when renaming a branch. Returns 0 if successful, non-zero
+ * otherwise.
+ */
+extern int replace_each_worktree_head_symref(const char *oldref, const char *newref);
+
 #endif

builtin/branch.c

@@ -552,8 +552,7 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 	if (recovery)
 		warning(_("Renamed a misnamed branch '%s' away"), oldref.buf + 11);
 
-	/* no need to pass logmsg here as HEAD didn't really move */
-	if (!strcmp(oldname, head) && create_symref("HEAD", newref.buf, NULL))
+	if (replace_each_worktree_head_symref(oldref.buf, newref.buf))
 		die(_("Branch renamed to %s, but HEAD is not updated!"), newname);
 
 	strbuf_addf(&oldsection, "branch.%s", oldref.buf + 11);

t/t3200-branch.sh

@@ -126,7 +126,28 @@ test_expect_success 'git branch -M foo bar should fail when bar is checked out'
 test_expect_success 'git branch -M baz bam should succeed when baz is checked out' '
 	git checkout -b baz &&
 	git branch bam &&
-	git branch -M baz bam
+	git branch -M baz bam &&
+	test $(git rev-parse --abbrev-ref HEAD) = bam
+'
+
+test_expect_success 'git branch -M baz bam should succeed when baz is checked out as linked working tree' '
+	git checkout master &&
+	git worktree add -b baz bazdir &&
+	git worktree add -f bazdir2 baz &&
+	git branch -M baz bam &&
+	test $(git -C bazdir rev-parse --abbrev-ref HEAD) = bam &&
+	test $(git -C bazdir2 rev-parse --abbrev-ref HEAD) = bam
+'
+
+test_expect_success 'git branch -M baz bam should succeed within a worktree in which baz is checked out' '
+	git checkout -b baz &&
+	git worktree add -f bazdir3 baz &&
+	(
+		cd bazdir3 &&
+		git branch -M baz bam &&
+		test $(git rev-parse --abbrev-ref HEAD) = bam
+	) &&
+	test $(git rev-parse --abbrev-ref HEAD) = bam
 '
 
 test_expect_success 'git branch -M master should work when master is checked out' '