bpo-32797: linecache should search for sources if loader doesn't find…

… them

Lib/linecache.py

@@ -104,15 +104,13 @@ def updatecache(filename, module_globals=None):
             except (ImportError, OSError):
                 pass
             else:
-                if data is None:
-                    # No luck, the PEP302 loader cannot find the source
-                    # for this module.
-                    return []
-                cache[filename] = (
-                    len(data), None,
-                    [line+'\n' for line in data.splitlines()], fullname
-                )
-                return cache[filename][2]
+                # If data is None, then the PEP302 loader didn't find
+                # sources. In that case, we still continue searching for
+                # the sources by filename (bpo-32797).
+                if data is not None:
+                    lines = [line + '\n' for line in data.splitlines()]
+                    cache[filename] = (len(data), None, lines, fullname)
+                    return lines
 
         # Try looking through the module search path, which is only useful
         # when handling a relative filename.

Lib/test/test_linecache.py

@@ -237,6 +237,17 @@ def raise_memoryerror(*args, **kwargs):
         self.assertEqual(lines3, [])
         self.assertEqual(linecache.getlines(FILENAME), lines)
 
+    def test_loader_get_source(self):
+        from types import ModuleType
+        from importlib.machinery import ExtensionFileLoader
+        mod = ModuleType("fake_io")
+        mod_globals = mod.__dict__
+        mod_globals["__loader__"] = ExtensionFileLoader("fake_io", "")
+
+        # bpo-32797: this should return the source code of "io.py" even
+        # though the loader's get_source() returns None.
+        self.assertTrue(linecache.getlines("io.py", mod_globals))
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2018-04-30-13-59-32.bpo-32797.6wOAdd.rst

@@ -0,0 +1,2 @@
+linecache continues searching for the source file by filename if the ``get_source``
+method of the ``__loader__`` returns ``None``.