From c0552b359c5b5dc0c130b831ce0067af99149f27 Mon Sep 17 00:00:00 2001
From: Yu Watanabe <watanabe.yu+github@gmail.com>
Date: Mon, 17 Apr 2023 05:04:27 +0900
Subject: [PATCH] chase: make chaseat() provides absolute path also when dir_fd
 points to the root directory

Usually, we pass the file descriptor of the root directory to chaseat()
when `--root=` is not specified. Previously, even in such case, the
result was relative, and we need to prefix the path with "/" when we
want to pass the path to other functions that do not support dir_fd, or
log or show the path. That's inconvenient.
---
 src/basic/chase.c     |  5 +++--
 src/test/test-chase.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/basic/chase.c b/src/basic/chase.c
index eb4bda07a6f..a6a37978e8f 100644
--- a/src/basic/chase.c
+++ b/src/basic/chase.c
@@ -190,8 +190,9 @@ int chaseat(int dir_fd, const char *path, ChaseFlags flags, char **ret_path, int
                 return -ENOMEM;
 
         /* If we receive an absolute path together with AT_FDCWD, we need to return an absolute path, because
-         * a relative path would be interpreted relative to the current working directory. */
-        bool need_absolute = dir_fd == AT_FDCWD && path_is_absolute(path);
+         * a relative path would be interpreted relative to the current working directory. Also, let's make
+         * the result absolute when the file descriptor of the root directory is specified. */
+        bool need_absolute = (dir_fd == AT_FDCWD && path_is_absolute(path)) || dir_fd_is_root(dir_fd) > 0;
         if (need_absolute) {
                 done = strdup("/");
                 if (!done)
diff --git a/src/test/test-chase.c b/src/test/test-chase.c
index 1e98f5c6ed2..52ea21a54c6 100644
--- a/src/test/test-chase.c
+++ b/src/test/test-chase.c
@@ -442,6 +442,34 @@ TEST(chaseat) {
         assert_se(streq(result, "/usr"));
         result = mfree(result);
 
+        /* If the file descriptor points to the root directory, the result will be absolute. */
+
+        fd = open("/", O_CLOEXEC | O_DIRECTORY | O_PATH);
+        assert_se(fd >= 0);
+
+        assert_se(chaseat(fd, p, 0, &result, NULL) >= 0);
+        assert_se(streq(result, "/usr"));
+        result = mfree(result);
+
+        assert_se(chaseat(fd, p, CHASE_AT_RESOLVE_IN_ROOT, &result, NULL) >= 0);
+        assert_se(streq(result, "/usr"));
+        result = mfree(result);
+
+        fd = safe_close(fd);
+
+        /* If the file descriptor does not point to the root directory, the result will be relative. */
+
+        assert_se(chaseat(tfd, "abc", CHASE_AT_RESOLVE_IN_ROOT, NULL, NULL) == -ENOENT);
+        assert_se(chaseat(tfd, "/abc", CHASE_AT_RESOLVE_IN_ROOT, NULL, NULL) == -ENOENT);
+
+        assert_se(chaseat(tfd, "abc", CHASE_AT_RESOLVE_IN_ROOT | CHASE_NONEXISTENT, &result, NULL) >= 0);
+        assert_se(streq(result, "usr"));
+        result = mfree(result);
+
+        assert_se(chaseat(tfd, "/abc", CHASE_AT_RESOLVE_IN_ROOT | CHASE_NONEXISTENT, &result, NULL) >= 0);
+        assert_se(streq(result, "usr"));
+        result = mfree(result);
+
         /* Test that absolute path or not are the same when resolving relative to a directory file
          * descriptor and that we always get a relative path back. */