worktree.c: check whether branch is rebased in another worktree

This function find_shared_symref() is used in a couple places:

1) in builtin/branch.c: it's used to detect if a branch is checked out
   elsewhere and refuse to delete the branch.

2) in builtin/notes.c: it's used to detect if a note is being merged in
   another worktree

3) in branch.c, the function die_if_checked_out() is actually used by
   "git checkout" and "git worktree add" to see if a branch is already
   checked out elsewhere and refuse the operation.

In cases 1 and 3, if a rebase is ongoing, "HEAD" will be in detached
mode, find_shared_symref() fails to detect it and declares "no branch is
checked out here", which is not really what we want.

This patch tightens the test. If the given symref is "HEAD", we try to
detect if rebase is ongoing. If so return the branch being rebased. This
makes checkout and branch delete operations safer because you can't
checkout a branch being rebased in another place, or delete it.

Special case for checkout. If the current branch is being rebased,
git-rebase.sh may use "git checkout" to abort and return back to the
original branch. The updated test in find_shared_symref() will prevent
that and "git rebase --abort" will fail as a result.
find_shared_symref() and die_if_checked_out() have to learn a new
option ignore_current_worktree to loosen the test a bit.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -334,12 +334,12 @@ void remove_branch_state(void)
 	unlink(git_path_squash_msg());
 }
 
-void die_if_checked_out(const char *branch)
+void die_if_checked_out(const char *branch, int ignore_current_worktree)
 {
 	const struct worktree *wt;
 
 	wt = find_shared_symref("HEAD", branch);
-	if (!wt)
+	if (!wt || (ignore_current_worktree && wt->is_current))
 		return;
 	skip_prefix(branch, "refs/heads/", &branch);
 	die(_("'%s' is already checked out at '%s'"),

branch.h

@@ -58,7 +58,7 @@ extern int read_branch_desc(struct strbuf *, const char *branch_name);
  * worktree and die (with a message describing its checkout location) if
  * it is.
  */
-extern void die_if_checked_out(const char *branch);
+extern void die_if_checked_out(const char *branch, int ignore_current_worktree);
 
 /*
  * Update all per-worktree HEADs pointing at the old ref to point the new ref.

builtin/checkout.c

@@ -1111,7 +1111,7 @@ static int checkout_branch(struct checkout_opts *opts,
 		char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
 		if (head_ref &&
 		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
-			die_if_checked_out(new->path);
+			die_if_checked_out(new->path, 1);
 		free(head_ref);
 	}
 

builtin/worktree.c

@@ -205,7 +205,7 @@ static int add_worktree(const char *path, const char *refname,
 	if (!opts->detach && !strbuf_check_branch_ref(&symref, refname) &&
 		 ref_exists(symref.buf)) { /* it's a branch */
 		if (!opts->force)
-			die_if_checked_out(symref.buf);
+			die_if_checked_out(symref.buf, 0);
 	} else { /* must be a commit */
 		commit = lookup_commit_reference_by_name(refname);
 		if (!commit)
@@ -349,7 +349,7 @@ static int add(int ac, const char **av, const char *prefix)
 		if (!opts.force &&
 		    !strbuf_check_branch_ref(&symref, opts.new_branch) &&
 		    ref_exists(symref.buf))
-			die_if_checked_out(symref.buf);
+			die_if_checked_out(symref.buf, 0);
 		strbuf_release(&symref);
 	}
 

t/t2025-worktree-add.sh

@@ -4,6 +4,8 @@ test_description='test git worktree add'
 
 . ./test-lib.sh
 
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
 test_expect_success 'setup' '
 	test_commit init
 '
@@ -225,4 +227,40 @@ test_expect_success '"add" worktree with --checkout' '
 	test_cmp init.t swamp2/init.t
 '
 
+test_expect_success 'put a worktree under rebase' '
+	git worktree add under-rebase &&
+	(
+		cd under-rebase &&
+		set_fake_editor &&
+		FAKE_LINES="edit 1" git rebase -i HEAD^ &&
+		git worktree list | grep "under-rebase.*detached HEAD"
+	)
+'
+
+test_expect_success 'add a worktree, checking out a rebased branch' '
+	test_must_fail git worktree add new-rebase under-rebase &&
+	! test -d new-rebase
+'
+
+test_expect_success 'checking out a rebased branch from another worktree' '
+	git worktree add new-place &&
+	test_must_fail git -C new-place checkout under-rebase
+'
+
+test_expect_success 'not allow to delete a branch under rebase' '
+	(
+		cd under-rebase &&
+		test_must_fail git branch -D under-rebase
+	)
+'
+
+test_expect_success 'check out from current worktree branch ok' '
+	(
+		cd under-rebase &&
+		git checkout under-rebase &&
+		git checkout - &&
+		git rebase --abort
+	)
+'
+
 test_done

worktree.c

@@ -3,6 +3,7 @@
 #include "strbuf.h"
 #include "worktree.h"
 #include "dir.h"
+#include "wt-status.h"
 
 void free_worktrees(struct worktree **worktrees)
 {
@@ -215,6 +216,30 @@ const char *get_worktree_git_dir(const struct worktree *wt)
 		return git_common_path("worktrees/%s", wt->id);
 }
 
+static int is_worktree_being_rebased(const struct worktree *wt,
+				     const char *target)
+{
+	struct wt_status_state state;
+	int found_rebase;
+
+	memset(&state, 0, sizeof(state));
+	found_rebase = wt_status_check_rebase(wt, &state) &&
+		((state.rebase_in_progress ||
+		  state.rebase_interactive_in_progress) &&
+		 state.branch &&
+		 starts_with(target, "refs/heads/") &&
+		 !strcmp(state.branch, target + strlen("refs/heads/")));
+	free(state.branch);
+	free(state.onto);
+	return found_rebase;
+}
+
+/*
+ * note: this function should be able to detect shared symref even if
+ * HEAD is temporarily detached (e.g. in the middle of rebase or
+ * bisect). New commands that do similar things should update this
+ * function as well.
+ */
 const struct worktree *find_shared_symref(const char *symref,
 					  const char *target)
 {
@@ -231,6 +256,13 @@ const struct worktree *find_shared_symref(const char *symref,
 	for (i = 0; worktrees[i]; i++) {
 		struct worktree *wt = worktrees[i];
 
+		if (wt->is_detached && !strcmp(symref, "HEAD")) {
+			if (is_worktree_being_rebased(wt, target)) {
+				existing = wt;
+				break;
+			}
+		}
+
 		strbuf_reset(&path);
 		strbuf_reset(&sb);
 		strbuf_addf(&path, "%s/%s",