Less dishonest COME_FROMs

Addresses all of the problems seen in 3.7 datetime.py.

However we limit COME_FROMs only to forward jumps, not back (which in the case of Python code right now means looping) jumps.

uncompyle6/parsers/parse36.py

@@ -33,6 +33,10 @@ class Python36Parser(Python35Parser):
         """
         sstmt ::= sstmt RETURN_LAST
 
+        cf_for_iter  ::= _come_froms FOR_ITER
+        list_for     ::= expr cf_for_iter store list_iter jb_or_c
+        genexpr_func ::= LOAD_FAST cf_for_iter store comp_iter JUMP_BACK
+
         # 3.6 redoes how return_closure works. FIXME: Isolate to LOAD_CLOSURE
         return_closure   ::= LOAD_CLOSURE DUP_TOP STORE_NAME RETURN_VALUE RETURN_LAST
 

uncompyle6/scanners/scanner3.py

@@ -811,7 +811,13 @@ class Scanner3(Scanner):
                             self.fixed_jumps[offset] = fix or match[-1]
                             return
                     else:
+                        if self.version < 3.6:
+                            # FIXME: this is putting in COME_FROMs in the wrong place.
+                            # Fix up grammar so we don't need to do this.
+                            # See cf_for_iter use in parser36.py
                             self.fixed_jumps[offset] = match[-1]
+                        else:
+                            self.fixed_jumps[offset] = target
                         return
             # op == POP_JUMP_IF_TRUE
             else:

uncompyle6/semantics/pysource.py

@@ -1433,7 +1433,7 @@ class SourceWalker(GenericASTTraversal, object):
             assert node[n].kind.startswith('CALL_FUNCTION')
 
             if node[n].kind.startswith('CALL_FUNCTION_KW'):
-                # 3.6+ starts does this
+                # 3.6+ starts doing this
                 kwargs = node[n-1].attr
                 assert isinstance(kwargs, tuple)
                 i = n - (len(kwargs)+1)