prefix_path: show gitdir if worktree unavailable

If there is no worktree at present, we can still hint the user about
Git's current directory by showing them the absolute path to the Git
directory. Even though the Git directory doesn't make it as easy to
locate the worktree in question, it can still help a user figure out
what's going on while developing a script.

This fixes a segmentation fault introduced in e0020b2f
("prefix_path: show gitdir when arg is outside repo", 2020-02-14).

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
[jc: added minimum tests, with help from Szeder Gábor]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pathspec.c

@@ -438,9 +438,13 @@ static void init_pathspec_item(struct pathspec_item *item, unsigned flags,
 	} else {
 		match = prefix_path_gently(prefix, prefixlen,
 					   &prefixlen, copyfrom);
-		if (!match)
+		if (!match) {
+			const char *hint_path = get_git_work_tree();
+			if (!hint_path)
+				hint_path = get_git_dir();
 			die(_("%s: '%s' is outside repository at '%s'"), elt,
-			    copyfrom, absolute_path(get_git_work_tree()));
+			    copyfrom, absolute_path(hint_path));
+		}
 	}
 
 	item->match = match;

setup.c

@@ -120,9 +120,13 @@ char *prefix_path_gently(const char *prefix, int len,
 char *prefix_path(const char *prefix, int len, const char *path)
 {
 	char *r = prefix_path_gently(prefix, len, NULL, path);
-	if (!r)
+	if (!r) {
+		const char *hint_path = get_git_work_tree();
+		if (!hint_path)
+			hint_path = get_git_dir();
 		die(_("'%s' is outside repository at '%s'"), path,
-		    absolute_path(get_git_work_tree()));
+		    absolute_path(hint_path));
+	}
 	return r;
 }
 

t/t6136-pathspec-in-bare.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+test_description='diagnosing out-of-scope pathspec'
+
+. ./test-lib.sh
+
+test_expect_success 'setup a bare and non-bare repository' '
+	test_commit file1 &&
+	git clone --bare . bare
+'
+
+test_expect_success 'log and ls-files in a bare repository' '
+	(
+		cd bare &&
+		test_must_fail git log -- .. >out 2>err &&
+		test_must_be_empty out &&
+		test_i18ngrep "outside repository" err &&
+
+		test_must_fail git ls-files -- .. >out 2>err &&
+		test_must_be_empty out &&
+		test_i18ngrep "outside repository" err
+	)
+'
+
+test_expect_success 'log and ls-files in .git directory' '
+	(
+		cd .git &&
+		test_must_fail git log -- .. >out 2>err &&
+		test_must_be_empty out &&
+		test_i18ngrep "outside repository" err &&
+
+		test_must_fail git ls-files -- .. >out 2>err &&
+		test_must_be_empty out &&
+		test_i18ngrep "outside repository" err
+	)
+'
+
+test_done