fix #8464 wrong root dir when -c is passed (#8537)

fix #8464 wrong root dir when -c is passed

AUTHORS

@@ -5,6 +5,7 @@ Contributors include::
 
 Aaron Coleman
 Abdeali JK
+Abdelrahman Elbehery
 Abhijeet Kasurde
 Adam Johnson
 Adam Uhlir

changelog/8464.bugfix.rst

@@ -0,0 +1 @@
+``-c <config file>`` now also properly defines ``rootdir`` as the directory that contains ``<config file>``.

doc/en/reference/customize.rst

@@ -145,6 +145,8 @@ Finding the ``rootdir``
 
 Here is the algorithm which finds the rootdir from ``args``:
 
+- If ``-c`` is passed in the command-line, use that as configuration file, and its directory as ``rootdir``.
+
 - Determine the common ancestor directory for the specified ``args`` that are
   recognised as paths that exist in the file system. If no such paths are
   found, the common ancestor directory is set to the current working directory.
@@ -160,7 +162,7 @@ Here is the algorithm which finds the rootdir from ``args``:
   ``setup.cfg`` in each of the specified ``args`` and upwards. If one is
   matched, it becomes the ``configfile`` and its directory becomes the ``rootdir``.
 
-- If no ``configfile`` was found, use the already determined common ancestor as root
+- If no ``configfile`` was found and no configuration argument is passed, use the already determined common ancestor as root
   directory. This allows the use of pytest in structures that are not part of
   a package and don't have any particular configuration file.
 

src/_pytest/config/findpaths.py

@@ -176,7 +176,7 @@ def determine_setup(
         inipath: Optional[Path] = inipath_
         inicfg = load_config_dict_from_file(inipath_) or {}
         if rootdir_cmd_arg is None:
-            rootdir = get_common_ancestor(dirs)
+            rootdir = inipath_.parent
     else:
         ancestor = get_common_ancestor(dirs)
         rootdir, inipath, inicfg = locate_config([ancestor])

testing/test_config.py

@@ -1405,6 +1405,26 @@ class TestRootdir:
         assert inipath == p
         assert ini_config == {"x": "10"}
 
+    def test_explicit_config_file_sets_rootdir(
+        self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        tests_dir = tmp_path / "tests"
+        tests_dir.mkdir()
+
+        monkeypatch.chdir(tmp_path)
+
+        # No config file is explicitly given: rootdir is determined to be cwd.
+        rootpath, found_inipath, *_ = determine_setup(None, [str(tests_dir)])
+        assert rootpath == tmp_path
+        assert found_inipath is None
+
+        # Config file is explicitly given: rootdir is determined to be inifile's directory.
+        inipath = tmp_path / "pytest.ini"
+        inipath.touch()
+        rootpath, found_inipath, *_ = determine_setup(str(inipath), [str(tests_dir)])
+        assert rootpath == tmp_path
+        assert found_inipath == inipath
+
     def test_with_arg_outside_cwd_without_inifile(
         self, tmp_path: Path, monkeypatch: MonkeyPatch
     ) -> None: