Don't fail if imp can't find the source for a .pyc file. #2038

AUTHORS

@@ -101,6 +101,7 @@ Michael Birtwell
 Michael Droettboom
 Michael Seifert
 Mike Lundy
+Ned Batchelder
 Nicolas Delaby
 Oleg Pidsadnyi
 Oliver Bestwalter

CHANGELOG.rst

@@ -5,12 +5,17 @@
 
 *
 
-*
+* Cope gracefully with a .pyc file with no matching .py file (`#2038`_). Thanks
+  `@nedbat`_.
 
 *
 
 *
 
+.. _@nedbat: https://github.com/nedbat
+
+.. _#2038: https://github.com/pytest-dev/pytest/issues/2038
+
 
 3.0.4
 =====

_pytest/assertion/rewrite.py

@@ -80,7 +80,12 @@ class AssertionRewritingHook(object):
             tp = desc[2]
             if tp == imp.PY_COMPILED:
                 if hasattr(imp, "source_from_cache"):
-                    fn = imp.source_from_cache(fn)
+                    try:
+                        fn = imp.source_from_cache(fn)
+                    except ValueError:
+                        # Python 3 doesn't like orphaned but still-importable
+                        # .pyc files.
+                        fn = fn[:-1]
                 else:
                     fn = fn[:-1]
             elif tp != imp.PY_SOURCE:

testing/test_assertrewrite.py

@@ -1,7 +1,10 @@
+import glob
 import os
+import py_compile
 import stat
 import sys
 import zipfile
+
 import py
 import pytest
 
@@ -480,6 +483,31 @@ def test_rewritten():
         monkeypatch.setenv("PYTHONDONTWRITEBYTECODE", "1")
         assert testdir.runpytest_subprocess().ret == 0
 
+    def test_orphaned_pyc_file(self, testdir):
+        if sys.version_info < (3, 0) and hasattr(sys, 'pypy_version_info'):
+            pytest.skip("pypy2 doesn't run orphaned pyc files")
+
+        testdir.makepyfile("""
+            import orphan
+            def test_it():
+                assert orphan.value == 17
+            """)
+        testdir.makepyfile(orphan="""
+            value = 17
+            """)
+        py_compile.compile("orphan.py")
+        os.remove("orphan.py")
+
+        # Python 3 puts the .pyc files in a __pycache__ directory, and will
+        # not import from there without source.  It will import a .pyc from
+        # the source location though.
+        if not os.path.exists("orphan.pyc"):
+            pycs = glob.glob("__pycache__/orphan.*.pyc")
+            assert len(pycs) == 1
+            os.rename(pycs[0], "orphan.pyc")
+
+        assert testdir.runpytest().ret == 0
+
     @pytest.mark.skipif('"__pypy__" in sys.modules')
     def test_pyc_vs_pyo(self, testdir, monkeypatch):
         testdir.makepyfile("""