Merge pull request #4153 from asottile/syntax_warning_filename

Display the filename when encountering `SyntaxWarning`.

changelog/4152.bugfix.rst

@@ -0,0 +1 @@
+Display the filename when encountering ``SyntaxWarning``.

src/_pytest/assertion/rewrite.py

@@ -398,7 +398,7 @@ def _rewrite_test(config, fn):
             finally:
                 del state._indecode
     try:
-        tree = ast.parse(source)
+        tree = ast.parse(source, filename=fn.strpath)
     except SyntaxError:
         # Let this pop up again in the real import.
         state.trace("failed to parse: %r" % (fn,))