Fix issue where working dir becomes wrong on subst drive on Windows. Fixes pytest-dev#5965

Author: fabioz

changelog/5965.bugfix.rst

@@ -0,0 +1 @@
+No longer resolve symlinks so that the current directory remains correct even with drives mapped with subst on Windows.

src/_pytest/config/__init__.py

@@ -208,7 +208,7 @@ def get_config(args=None, plugins=None):
     config = Config(
         pluginmanager,
         invocation_params=Config.InvocationParams(
-            args=args or (), plugins=plugins, dir=Path().resolve()
+            args=args or (), plugins=plugins, dir=Path.cwd()
         ),
     )
 
@@ -462,7 +462,13 @@ def _getconftestmodules(self, path):
         # and allow users to opt into looking into the rootdir parent
         # directories instead of requiring to specify confcutdir
         clist = []
-        for parent in directory.realpath().parts():
+        
+        p = directory
+        if sys.platform != 'win32':
+            # Only resolve symlinks if not on windows. See: #5965
+            p = p.realpath()
+
+        for parent in p.parts():
             if self._confcutdir and self._confcutdir.relto(parent):
                 continue
             conftestpath = parent.join("conftest.py")
@@ -771,7 +777,7 @@ def __init__(self, pluginmanager, *, invocation_params=None) -> None:
 
         if invocation_params is None:
             invocation_params = self.InvocationParams(
-                args=(), plugins=None, dir=Path().resolve()
+                args=(), plugins=None, dir=Path.cwd()
             )
 
         self.option = argparse.Namespace()

src/_pytest/fixtures.py

@@ -1288,7 +1288,10 @@ def getfixtureinfo(self, node, func, cls, funcargs=True):
     def pytest_plugin_registered(self, plugin):
         nodeid = None
         try:
-            p = py.path.local(plugin.__file__).realpath()
+            p = py.path.local(plugin.__file__)
+            if sys.platform != 'win32':
+                # Only resolve symlinks if not on windows. See: #5965
+                p = p.realpath()
         except AttributeError:
             pass
         else:

src/_pytest/main.py

@@ -642,7 +642,11 @@ def _parsearg(self, arg):
                     "file or package not found: " + arg + " (missing __init__.py?)"
                 )
             raise UsageError("file not found: " + arg)
-        fspath = fspath.realpath()
+
+        if sys.platform != 'win32':
+            # Only resolve symlinks if not on windows. See: #5965
+            fspath = fspath.realpath()
+
         return (fspath, parts)
 
     def matchnodes(self, matching, names):

testing/test_windows_subst.py

@@ -0,0 +1,95 @@
+import os.path
+import subprocess
+import sys
+from string import ascii_lowercase
+
+from py._path.local import LocalPath
+
+import pytest
+from _pytest import pytester
+from _pytest.fixtures import FixtureRequest
+
+
+class _SubstTmpdirFactory:
+    """
+    A temp dir factory which may do a subst on Windows drives.
+    """
+
+    def __init__(self, tmpdir, tmpdir_factory, subst):
+        self.tmpdir = tmpdir
+        self.tmpdir_factory = tmpdir_factory
+        self.subst = subst
+        self.subst_drives = {}
+
+    def _subst_path(self, filename):
+
+        if self.subst:
+            for c in ascii_lowercase[7:]:  # Create a subst drive from H-Z.
+                c += ":"
+                if not os.path.exists(c):
+                    drive = c
+                    break
+            else:
+                raise AssertionError("Unable to find suitable drive letter for subst.")
+
+            directory = os.path.dirname(filename)
+            basename = os.path.basename(filename)
+
+            args = ["subst", drive, directory]
+            subprocess.check_call(args)
+            assert os.path.exists(drive)
+            self.subst_drives[drive] = directory
+
+            filename = LocalPath(os.path.join(drive, basename))
+
+        return filename
+
+    def mktemp(self, name, numbered):
+        filename = self.tmpdir_factory.mktemp(name, numbered=numbered)
+        filename = self._subst_path(filename)
+        return filename
+
+    def unsubst(self):
+        for drive in self.subst_drives:
+            args = ["subst", "/D", drive]
+            subprocess.check_call(args)
+
+
+@pytest.fixture(params=[{"subst": True}, {"subst": False}])
+def _subst_tmpdir_factory(request: FixtureRequest, tmpdir, tmpdir_factory):
+    if sys.platform != "win32":
+        pytest.skip("Windows only test.")
+    factory = _SubstTmpdirFactory(tmpdir, tmpdir_factory, **request.param)
+    yield factory
+    factory.unsubst()
+
+
+@pytest.fixture
+def _custom_testdir(
+    request: FixtureRequest, _subst_tmpdir_factory
+) -> "pytester.Testdir":
+    return pytester.Testdir(request, _subst_tmpdir_factory)
+
+
+def test_windows_subst_resolve(_custom_testdir, _subst_tmpdir_factory) -> None:
+    """
+    Check that when we have a subst on Windows the errors reported are not
+    in the subst target.
+    See: https://github.com/pytest-dev/pytest/issues/5965
+    """
+    testdir = _custom_testdir
+    testdir.makepyfile(
+        """
+        import pytest
+        def test_foo():
+            raise AssertionError()
+        """
+    )
+    result = testdir.runpytest()
+
+    # i.e.: Make sure that the error is reported as a relative path, not as an
+    # absolute (resolved) path.
+    # See: https://github.com/pytest-dev/pytest/issues/5965
+    for _drive, directory in _subst_tmpdir_factory.subst_drives.items():
+        for line in result.stdout.lines:
+            assert directory.lower() not in line.lower()