[PATCH] branch: report kind of checkout when rejecting delete

["René Scharfe" <l.s.r@web.de>]

git branch refuses to delete branches that are currently checked out
with a message like this: "error: cannot delete branch 'foo' used by
worktree at '/path/of/worktree'".  This can be confusing with internal
checkouts, e.g. if one tries to delete a branch associated with an
active bisect run.

Mention the kind of internal checkout, if any, to spare the user from
remembering that they might have forgotten a bisect or rebase.  To do
that, register the checkout reason in a strintmap alongside the existing
strmap that stores the worktree path.

Suggested-by: stsp <stsp2@yandex.ru>
Signed-off-by: René Scharfe <l.s.r@web.de>
---
Original message:
https://lore.kernel.org/git/cae34516-5437-49d3-8d39-16f4059a81a8@yandex.ru/

 branch.c          | 48 ++++++++++++++++++++++++++---------------------
 branch.h          | 15 +++++++++++++++
 builtin/branch.c  | 31 +++++++++++++++++++++++++++---
 t/t3200-branch.sh |  4 ++--
 4 files changed, 72 insertions(+), 26 deletions(-)

diff --git a/branch.c b/branch.c
index 243db7d0fc..aaa54f1b62 100644
--- a/branch.c
+++ b/branch.c
@@ -384,6 +384,16 @@ int validate_branchname(const char *name, struct strbuf *ref)
 
 static int initialized_checked_out_branches;
 static struct strmap current_checked_out_branches = STRMAP_INIT;
+static struct strintmap current_checked_out_branch_kinds = STRINTMAP_INIT;
+
+static void register_checked_out_branch(const char *refname, const char *path,
+					enum branch_checkout_kind kind)
+{
+	char *old = strmap_put(&current_checked_out_branches, refname,
+			       xstrdup(path));
+	free(old);
+	strintmap_set(&current_checked_out_branch_kinds, refname, kind);
+}
 
 static void prepare_checked_out_branches(void)
 {
@@ -397,7 +407,7 @@ static void prepare_checked_out_branches(void)
 	worktrees = get_worktrees();
 
 	while (worktrees[i]) {
-		char *old, *wt_gitdir;
+		char *wt_gitdir;
 		struct wt_status_state state = { 0 };
 		struct worktree *wt = worktrees[i++];
 		struct string_list update_refs = STRING_LIST_INIT_DUP;
@@ -405,22 +415,17 @@ static void prepare_checked_out_branches(void)
 		if (wt->is_bare)
 			continue;
 
-		if (wt->head_ref) {
-			old = strmap_put(&current_checked_out_branches,
-					 wt->head_ref,
-					 xstrdup(wt->path));
-			free(old);
-		}
+		if (wt->head_ref)
+			register_checked_out_branch(wt->head_ref, wt->path,
+				BRANCH_CHECKOUT_KIND_CHECKOUT);
 
 		if (wt_status_check_rebase(wt, &state) &&
 		    (state.rebase_in_progress || state.rebase_interactive_in_progress) &&
 		    state.branch) {
 			struct strbuf ref = STRBUF_INIT;
 			strbuf_addf(&ref, "refs/heads/%s", state.branch);
-			old = strmap_put(&current_checked_out_branches,
-					 ref.buf,
-					 xstrdup(wt->path));
-			free(old);
+			register_checked_out_branch(ref.buf, wt->path,
+				BRANCH_CHECKOUT_KIND_REBASE);
 			strbuf_release(&ref);
 		}
 		wt_status_state_free_buffers(&state);
@@ -429,10 +434,8 @@ static void prepare_checked_out_branches(void)
 		    state.bisecting_from) {
 			struct strbuf ref = STRBUF_INIT;
 			strbuf_addf(&ref, "refs/heads/%s", state.bisecting_from);
-			old = strmap_put(&current_checked_out_branches,
-					 ref.buf,
-					 xstrdup(wt->path));
-			free(old);
+			register_checked_out_branch(ref.buf, wt->path,
+				BRANCH_CHECKOUT_KIND_BISECT);
 			strbuf_release(&ref);
 		}
 		wt_status_state_free_buffers(&state);
@@ -441,12 +444,9 @@ static void prepare_checked_out_branches(void)
 		if (!sequencer_get_update_refs_state(wt_gitdir,
 						     &update_refs)) {
 			struct string_list_item *item;
-			for_each_string_list_item(item, &update_refs) {
-				old = strmap_put(&current_checked_out_branches,
-						 item->string,
-						 xstrdup(wt->path));
-				free(old);
-			}
+			for_each_string_list_item(item, &update_refs)
+				register_checked_out_branch(item->string, wt->path,
+					BRANCH_CHECKOUT_KIND_UPDATE_REF);
 			string_list_clear(&update_refs, 1);
 		}
 
@@ -462,6 +462,12 @@ const char *branch_checked_out(const char *refname)
 	return strmap_get(&current_checked_out_branches, refname);
 }
 
+enum branch_checkout_kind branch_checkout_kind(const char *refname)
+{
+	prepare_checked_out_branches();
+	return strintmap_get(&current_checked_out_branch_kinds, refname);
+}
+
 /*
  * Check if a branch 'name' can be created as a new branch; die otherwise.
  * 'force' can be used when it is OK for the named branch already exists.
diff --git a/branch.h b/branch.h
index 3dc6e2a0ff..d1073fe1cd 100644
--- a/branch.h
+++ b/branch.h
@@ -15,6 +15,14 @@ enum branch_track {
 	BRANCH_TRACK_SIMPLE,
 };
 
+enum branch_checkout_kind {
+	BRANCH_CHECKOUT_KIND_UNSPECIFIED = 0,
+	BRANCH_CHECKOUT_KIND_CHECKOUT,
+	BRANCH_CHECKOUT_KIND_REBASE,
+	BRANCH_CHECKOUT_KIND_BISECT,
+	BRANCH_CHECKOUT_KIND_UPDATE_REF,
+};
+
 /* Functions for acting on the information about branches. */
 
 /**
@@ -106,6 +114,13 @@ void create_branches_recursively(struct repository *r, const char *name,
  */
 const char *branch_checked_out(const char *refname);
 
+/*
+ * If the branch at 'refname' is currently checked out in a worktree,
+ * then return the kind of checkout, i.e. whether it was done by an
+ * actual checkout or a rebase etc.
+ */
+enum branch_checkout_kind branch_checkout_kind(const char *refname);
+
 /*
  * Check if 'name' can be a valid name for a branch; die otherwise.
  * Return 1 if the named branch already exists; return 0 otherwise.
diff --git a/builtin/branch.c b/builtin/branch.c
index dede60d27b..3223347129 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -266,9 +266,34 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 		if (kinds == FILTER_REFS_BRANCHES) {
 			const char *path;
 			if ((path = branch_checked_out(name))) {
-				error(_("cannot delete branch '%s' "
-					"used by worktree at '%s'"),
-				      bname.buf, path);
+				int kind = branch_checkout_kind(name);
+				switch (kind) {
+				case BRANCH_CHECKOUT_KIND_CHECKOUT:
+					error(_("cannot delete branch '%s' "
+						"used by worktree at '%s'"),
+					      bname.buf, path);
+					break;
+				case BRANCH_CHECKOUT_KIND_REBASE:
+					error(_("cannot delete branch '%s' "
+						"used by worktree at '%s' "
+						"for rebase"),
+					      bname.buf, path);
+					break;
+				case BRANCH_CHECKOUT_KIND_BISECT:
+					error(_("cannot delete branch '%s' "
+						"used by worktree at '%s' "
+						"for bisect"),
+					      bname.buf, path);
+					break;
+				case BRANCH_CHECKOUT_KIND_UPDATE_REF:
+					error(_("cannot delete branch '%s' "
+						"used by worktree at '%s' "
+						"for update-ref"),
+					      bname.buf, path);
+					break;
+				default:
+					BUG("invalid checkout kind %d", kind);
+				}
 				ret = 1;
 				continue;
 			}
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index e2682a83a0..e5df493b66 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -930,7 +930,7 @@ test_expect_success 'deleting currently checked out branch fails' '
 	git worktree add -b my7 my7 &&
 	test_must_fail git -C my7 branch -d my7 &&
 	test_must_fail git branch -d my7 2>actual &&
-	grep "^error: cannot delete branch .my7. used by worktree at " actual &&
+	test_grep "^error: cannot delete branch '"'"'my7'"'"' used by worktree at '"'.*'\$"'" actual &&
 	rm -r my7 &&
 	git worktree prune
 '
@@ -941,7 +941,7 @@ test_expect_success 'deleting in-use branch fails' '
 	git -C my7 bisect start HEAD HEAD~2 &&
 	test_must_fail git -C my7 branch -d my7 &&
 	test_must_fail git branch -d my7 2>actual &&
-	grep "^error: cannot delete branch .my7. used by worktree at " actual &&
+	test_grep "^error: cannot delete branch '"'"'my7'"'"' used by worktree at '"'.*' for bisect\$"'" actual &&
 	rm -r my7 &&
 	git worktree prune
 '
-- 
2.55.0