Don't crash on unexpected PY2 except syntax (#4011)

Rather than supporting esoteric forms like `except Ex, (err, info)` we just generate an error. At least it should no longer be possible to generate a crash this way.

Author: gvanrossum

mypy/fastparse2.py

@@ -586,15 +586,16 @@ def try_handler(self,
                     orelse: List[ast27.stmt],
                     finalbody: List[ast27.stmt],
                     lineno: int) -> TryStmt:
-        def produce_name(item: ast27.ExceptHandler) -> Optional[NameExpr]:
+        vs = []  # type: List[Optional[NameExpr]]
+        for item in handlers:
             if item.name is None:
-                return None
+                vs.append(None)
             elif isinstance(item.name, ast27.Name):
-                return NameExpr(item.name.id)
+                vs.append(NameExpr(item.name.id))
             else:
-                raise RuntimeError("'{}' has non-Name name.".format(ast27.dump(item)))
-
-        vs = [produce_name(h) for h in handlers]
+                self.fail("Sorry, `except <expr>, <anything but a name>` is not supported",
+                          item.lineno, item.col_offset)
+                vs.append(None)
         types = [self.visit(h.type) for h in handlers]
         handlers_ = [self.as_required_block(h.body, h.lineno) for h in handlers]
 

test-data/unit/check-python2.test

@@ -77,6 +77,21 @@ except BaseException, e:
     e() # E: "BaseException" not callable
 [builtins_py2 fixtures/exception.pyi]
 
+[case testTryExceptUnsupported]
+try:
+    pass
+except BaseException, (e, f):  # E: Sorry, `except <expr>, <anything but a name>` is not supported
+    pass
+try:
+    pass
+except BaseException, [e, f, g]:  # E: Sorry, `except <expr>, <anything but a name>` is not supported
+    pass
+try:
+    pass
+except BaseException, e[0]:  # E: Sorry, `except <expr>, <anything but a name>` is not supported
+    pass
+[builtins_py2 fixtures/exception.pyi]
+
 [case testAlternateNameSuggestions]
 class Foo(object):
     def say_hello(self):