prune --worktrees: fix expire vs worktree existence condition

`git prune --worktrees` was pruning worktrees which were non-existent OR
expired, while it rather should prune those which are orphaned AND
expired, as git-checkout documentation describes. Fix it.

Add test 'not prune proper checkouts', which uses valid but expired
worktree.

Modify test 'not prune recent checkouts' to remove the worktree before
pruning - link in worktrees still must survive. In older form it is
useless because would pass always when the other test passes.
Signed-off-by: NMax Kirillov <max@max630.net>
Acked-by: NDuy Nguyen <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/prune.c

@@ -120,11 +120,15 @@ static int prune_worktree(const char *id, struct strbuf *reason)
 		if (!stat(git_path("worktrees/%s/link", id), &st_link) &&
 		    st_link.st_nlink > 1)
 			return 0;
-		strbuf_addf(reason, _("Removing worktrees/%s: gitdir file points to non-existent location"), id);
-		return 1;
+		if (st.st_mtime <= expire) {
+			strbuf_addf(reason, _("Removing worktrees/%s: gitdir file points to non-existent location"), id);
+			return 1;
+		} else {
+			return 0;
+		}
 	}
 	free(path);
-	return st.st_mtime <= expire;
+	return 0;
 }
 
 static void prune_worktrees(void)

t/t2026-prune-linked-checkouts.sh

@@ -4,6 +4,10 @@ test_description='prune $GIT_DIR/worktrees'
 
 . ./test-lib.sh
 
+test_expect_success initialize '
+	git commit --allow-empty -m init
+'
+
 test_expect_success 'prune --worktrees on normal repo' '
 	git prune --worktrees &&
 	test_must_fail git prune --worktrees abc
@@ -77,8 +81,16 @@ test_expect_success 'not prune recent checkouts' '
 	mkdir zz &&
 	mkdir -p .git/worktrees/jlm &&
 	echo "$(pwd)"/zz >.git/worktrees/jlm/gitdir &&
+	rmdir zz &&
 	git prune --worktrees --verbose --expire=2.days.ago &&
 	test -d .git/worktrees/jlm
 '
 
+test_expect_success 'not prune proper checkouts' '
+	test_when_finished rm -r .git/worktrees &&
+	git checkout "--to=$PWD/nop" --detach master &&
+	git prune --worktrees &&
+	test -d .git/worktrees/nop
+'
+
 test_done