wt-status: avoid passing NULL worktree

In preparation for removing the repository argument from
worktree_git_path() add a function to construct a "struct worktree"
from a "struct repository" using its "gitdir" and "worktree"
members. This function is then used to avoid passing a NULL worktree to
wt_status_check_bisect() and wt_status_check_rebase(). In general the
"struct worktree" returned may not correspond to the "current" worktree
defined by is_current_worktree() as that function uses "the_repository"
rather than "wt->repo" when deciding which worktree is "current". In
practice the "struct repository" we pass corresponds to "the_repository"
as we only ever operate on a single repository at the moment.

wt_status_check_bisect() and wt_status_check_rebase() have the following
callers:

 - branch.c:prepare_checked_out_branches() which loops over all
   worktrees.

 - worktree.c:is_worktree_being_rebased() which is called from
   builtin/branch.c:reject_rebase_or_bisect_branch() that loops over all
   worktrees and worktree.c:is_shared_symref() which dereferences wt
   earlier in the function.

 - wt-status:wt_status_get_state() which is updated to avoid passing a
   NULL worktree by this patch.

This updates the only callers that pass a NULL worktree to
worktree_git_path(). A new test is added to check that "git status"
detects a rebase in a linked worktree.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: phillipwood

t/t7512-status-help.sh

@@ -594,6 +594,15 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'rebase in a linked worktree' '
+	test_might_fail git rebase --abort &&
+	git worktree add wt &&
+	test_when_finished "test_might_fail git -C wt rebase --abort;
+				git worktree remove wt" &&
+	GIT_SEQUENCE_EDITOR="echo break >" git -C wt rebase -i HEAD &&
+	git -C wt status >actual &&
+	test_grep "interactive rebase in progress" actual
+'
 
 test_expect_success 'prepare am_session' '
 	git reset --hard main &&

worktree.c

@@ -66,6 +66,26 @@ static int is_current_worktree(struct worktree *wt)
 	return is_current;
 }
 
+struct worktree *get_worktree_from_repository(struct repository *repo)
+{
+	struct worktree *wt = xcalloc(1, sizeof(*wt));
+	char *gitdir = absolute_pathdup(repo->gitdir);
+	char *commondir = absolute_pathdup(repo->commondir);
+
+	wt->repo = repo;
+	wt->path = absolute_pathdup(repo->worktree ? repo->worktree
+						   : repo->gitdir);
+	wt->is_bare = !repo->worktree;
+	if (fspathcmp(gitdir, commondir))
+		wt->id = xstrdup(find_last_dir_sep(gitdir) + 1);
+	wt->is_current = is_current_worktree(wt);
+	add_head_info(wt);
+
+	free(gitdir);
+	free(commondir);
+	return wt;
+}
+
 /*
 * When in a secondary worktree, and when extensions.worktreeConfig
 * is true, only $commondir/config and $commondir/worktrees/<id>/

worktree.h

@@ -38,6 +38,12 @@ struct worktree **get_worktrees(void);
  */
 struct worktree **get_worktrees_without_reading_head(void);
 
+/*
+ * Construct a struct worktree corresponding to repo->gitdir and
+ * repo->worktree.
+ */
+struct worktree *get_worktree_from_repository(struct repository *repo);
+
 /*
  * Returns 1 if linked worktrees exist, 0 otherwise.
  */

wt-status.c

@@ -1723,6 +1723,9 @@ int wt_status_check_rebase(const struct worktree *wt,
 {
 	struct stat st;
 
+	if (!wt)
+		BUG("wt_status_check_rebase() called with NULL worktree");
+
 	if (!stat(worktree_git_path(the_repository, wt, "rebase-apply"), &st)) {
 		if (!stat(worktree_git_path(the_repository, wt, "rebase-apply/applying"), &st)) {
 			state->am_in_progress = 1;
@@ -1750,6 +1753,9 @@ int wt_status_check_bisect(const struct worktree *wt,
 {
 	struct stat st;
 
+	if (!wt)
+		BUG("wt_status_check_bisect() called with NULL worktree");
+
 	if (!stat(worktree_git_path(the_repository, wt, "BISECT_LOG"), &st)) {
 		state->bisect_in_progress = 1;
 		state->bisecting_from = get_branch(wt, "BISECT_START");
@@ -1795,18 +1801,19 @@ void wt_status_get_state(struct repository *r,
 	struct stat st;
 	struct object_id oid;
 	enum replay_action action;
+	struct worktree *wt = get_worktree_from_repository(r);
 
 	if (!stat(git_path_merge_head(r), &st)) {
-		wt_status_check_rebase(NULL, state);
+		wt_status_check_rebase(wt, state);
 		state->merge_in_progress = 1;
-	} else if (wt_status_check_rebase(NULL, state)) {
+	} else if (wt_status_check_rebase(wt, state)) {
 		;		/* all set */
 	} else if (refs_ref_exists(get_main_ref_store(r), "CHERRY_PICK_HEAD") &&
 		   !repo_get_oid(r, "CHERRY_PICK_HEAD", &oid)) {
 		state->cherry_pick_in_progress = 1;
 		oidcpy(&state->cherry_pick_head_oid, &oid);
 	}
-	wt_status_check_bisect(NULL, state);
+	wt_status_check_bisect(wt, state);
 	if (refs_ref_exists(get_main_ref_store(r), "REVERT_HEAD") &&
 	    !repo_get_oid(r, "REVERT_HEAD", &oid)) {
 		state->revert_in_progress = 1;
@@ -1824,6 +1831,8 @@ void wt_status_get_state(struct repository *r,
 	if (get_detached_from)
 		wt_status_get_detached_from(r, state);
 	wt_status_check_sparse_checkout(r, state);
+
+	free_worktree(wt);
 }
 
 static void wt_longstatus_print_state(struct wt_status *s)