Fix `sys.modules` for failed imports in Python 2.7

Newly imported modules with compile and/or run-time errors were not being
removed from `sys.modules`.  This commit modifies the Python 2.7 loader so that
it follows Python's failed-initial-import logic and removes the module from
`sys.modules`.

hy/importer.py

@@ -293,7 +293,8 @@ else:
                     mod_type == imp.PKG_DIRECTORY and
                     os.path.isfile(pkg_path)):
 
-                if fullname in sys.modules:
+                was_in_sys = fullname in sys.modules
+                if was_in_sys:
                     mod = sys.modules[fullname]
                 else:
                     mod = sys.modules.setdefault(
@@ -311,7 +312,15 @@ else:
 
                 mod.__name__ = fullname
 
-                self.exec_module(mod, fullname=fullname)
+                try:
+                    self.exec_module(mod, fullname=fullname)
+                except Exception:
+                    # Follow Python 2.7 logic and only remove a new, bad
+                    # module; otherwise, leave the old--and presumably
+                    # good--module in there.
+                    if not was_in_sys:
+                        del sys.modules[fullname]
+                    raise
 
             if mod is None:
                 self._reopen()
@@ -385,7 +394,7 @@ else:
                     self.code = self.byte_compile_hy(fullname)
 
             if self.code is None:
-              super(HyLoader, self).get_code(fullname=fullname)
+                super(HyLoader, self).get_code(fullname=fullname)
 
             return self.code
 

tests/importer/test_importer.py

@@ -5,7 +5,6 @@
 import os
 import sys
 import ast
-import imp
 import tempfile
 import runpy
 import importlib
@@ -15,12 +14,16 @@ from fractions import Fraction
 import pytest
 
 import hy
-from hy._compat import bytes_type
 from hy.errors import HyTypeError
 from hy.lex import LexException
 from hy.compiler import hy_compile
 from hy.importer import hy_parse, HyLoader, cache_from_source
 
+try:
+    from importlib import reload
+except ImportError:
+    from imp import reload
+
 
 def test_basics():
     "Make sure the basics of the importer work"
@@ -85,6 +88,15 @@ def test_import_error_reporting():
     assert _import_error_test() is not None
 
 
+def test_import_error_cleanup():
+    "Failed initial imports should not leave dead modules in `sys.modules`."
+
+    with pytest.raises(hy.errors.HyMacroExpansionError):
+        importlib.import_module('tests.resources.fails')
+
+    assert 'tests.resources.fails' not in sys.modules
+
+
 @pytest.mark.skipif(sys.dont_write_bytecode,
                     reason="Bytecode generation is suppressed")
 def test_import_autocompiles():
@@ -127,7 +139,13 @@ def test_eval():
 
 
 def test_reload():
-    """Copied from CPython's `test_import.py`"""
+    """Generate a test module, confirm that it imports properly (and puts the
+    module in `sys.modules`), then modify the module so that it produces an
+    error when reloaded.  Next, fix the error, reload, and check that the
+    module is updated and working fine.  Rinse, repeat.
+
+    This test is adapted from CPython's `test_import.py`.
+    """
 
     def unlink(filename):
         os.unlink(source)
@@ -160,7 +178,7 @@ def test_reload():
             f.write("(setv b (// 20 0))")
 
         with pytest.raises(ZeroDivisionError):
-            imp.reload(mod)
+            reload(mod)
 
         # But we still expect the module to be in sys.modules.
         mod = sys.modules.get(TESTFN)
@@ -178,7 +196,7 @@ def test_reload():
             f.write("(setv a 11)")
             f.write("(setv b (// 20 1))")
 
-        imp.reload(mod)
+        reload(mod)
 
         mod = sys.modules.get(TESTFN)
         assert mod is not None
@@ -186,15 +204,17 @@ def test_reload():
         assert mod.a == 11
         assert mod.b == 20
 
-        # Now cause a LexException
+        # Now cause a `LexException`, and confirm that the good module and its
+        # contents stick around.
         unlink(source)
 
         with open(source, "w") as f:
+            # Missing paren...
             f.write("(setv a 11")
             f.write("(setv b (// 20 1))")
 
         with pytest.raises(LexException):
-            imp.reload(mod)
+            reload(mod)
 
         mod = sys.modules.get(TESTFN)
         assert mod is not None
@@ -209,7 +229,7 @@ def test_reload():
             f.write("(setv a 12)")
             f.write("(setv b (// 10 1))")
 
-        imp.reload(mod)
+        reload(mod)
 
         mod = sys.modules.get(TESTFN)
         assert mod is not None
@@ -219,8 +239,9 @@ def test_reload():
 
     finally:
         del sys.path[0]
+        if TESTFN in sys.modules:
+            del sys.modules[TESTFN]
         unlink(source)
-        del sys.modules[TESTFN]
 
 
 def test_circular():

tests/resources/fails.hy

@@ -0,0 +1,5 @@
+"This module produces an error when imported."
+(defmacro a-macro [x]
+  (+ x 1))
+
+(print (a-macro 'blah))