Don't crash with --pyargs and a filename that looks like a modu… (#5503)

Don't crash with --pyargs and a filename that looks like a module

src/_pytest/main.py

@@ -631,7 +631,10 @@ class Session(nodes.FSCollector):
         """Convert a dotted module name to path."""
         try:
             spec = importlib.util.find_spec(x)
-        except (ValueError, ImportError):
+        # AttributeError: looks like package module, but actually filename
+        # ImportError: module does not exist
+        # ValueError: not a module name
+        except (AttributeError, ImportError, ValueError):
             return x
         if spec is None or spec.origin in {None, "namespace"}:
             return x

testing/acceptance_test.py

@@ -646,6 +646,12 @@ class TestInvocationVariants:
         # should only configure once
         assert result.outlines.count("configuring") == 1
 
+    def test_pyargs_filename_looks_like_module(self, testdir):
+        testdir.tmpdir.join("conftest.py").ensure()
+        testdir.tmpdir.join("t.py").write("def test(): pass")
+        result = testdir.runpytest("--pyargs", "t.py")
+        assert result.ret == ExitCode.OK
+
     def test_cmdline_python_package(self, testdir, monkeypatch):
         import warnings