Repair compilation error for nested module level comprehensions.

Closes #1906.

Cython/Compiler/ExprNodes.py

@@ -7949,8 +7949,7 @@ class ScopedExprNode(ExprNode):
         generate_inner_evaluation_code(code)
 
         # normal (non-error) exit
-        for entry in py_entries:
-            code.put_var_xdecref_clear(entry)
+        self._generate_vars_cleanup(code, py_entries)
 
         # error/loop body exit points
         exit_scope = code.new_label('exit_scope')
@@ -7959,8 +7958,7 @@ class ScopedExprNode(ExprNode):
                                  list(zip(code.get_loop_labels(), old_loop_labels))):
             if code.label_used(label):
                 code.put_label(label)
-                for entry in py_entries:
-                    code.put_var_xdecref_clear(entry)
+                self._generate_vars_cleanup(code, py_entries)
                 code.put_goto(old_label)
         code.put_label(exit_scope)
         code.putln('} /* exit inner scope */')
@@ -7968,6 +7966,14 @@ class ScopedExprNode(ExprNode):
         code.set_loop_labels(old_loop_labels)
         code.error_label = old_error_label
 
+    def _generate_vars_cleanup(self, code, py_entries):
+        for entry in py_entries:
+            if entry.is_cglobal:
+                code.put_var_gotref(entry)
+                code.put_decref_set(entry.cname, "Py_None")
+            else:
+                code.put_var_xdecref_clear(entry)
+
 
 class ComprehensionNode(ScopedExprNode):
     # A list/set/dict comprehension

Cython/Compiler/Symtab.py

@@ -1704,7 +1704,10 @@ class LocalScope(Scope):
         # Return None if not found.
         entry = Scope.lookup(self, name)
         if entry is not None:
-            if entry.scope is not self and entry.scope.is_closure_scope:
+            entry_scope = entry.scope
+            while entry_scope.is_genexpr_scope:
+                entry_scope = entry_scope.outer_scope
+            if entry_scope is not self and entry_scope.is_closure_scope:
                 if hasattr(entry.scope, "scope_class"):
                     raise InternalError("lookup() after scope class created.")
                 # The actual c fragment for the different scopes differs
@@ -1740,8 +1743,12 @@ class GeneratorExpressionScope(Scope):
     is_genexpr_scope = True
 
     def __init__(self, outer_scope):
-        name = outer_scope.global_scope().next_id(Naming.genexpr_id_ref)
-        Scope.__init__(self, name, outer_scope, outer_scope)
+        parent_scope = outer_scope
+        # TODO: also ignore class scopes?
+        while parent_scope.is_genexpr_scope:
+            parent_scope = parent_scope.parent_scope
+        name = parent_scope.global_scope().next_id(Naming.genexpr_id_ref)
+        Scope.__init__(self, name, outer_scope, parent_scope)
         self.directives = outer_scope.directives
         self.genexp_prefix = "%s%d%s" % (Naming.pyrex_prefix, len(name), name)
 
@@ -1768,7 +1775,10 @@ class GeneratorExpressionScope(Scope):
         cname = '%s%s' % (self.genexp_prefix, self.parent_scope.mangle(Naming.var_prefix, name or self.next_id()))
         entry = self.declare(name, cname, type, pos, visibility)
         entry.is_variable = True
-        entry.is_local = True
+        if self.parent_scope.is_module_scope:
+            entry.is_cglobal = True
+        else:
+            entry.is_local = True
         entry.in_subscope = True
         self.var_entries.append(entry)
         self.entries[name] = entry

tests/run/dictcomp.pyx

@@ -57,3 +57,35 @@ def sorted(it):
     l = list(it)
     l.sort()
     return l
+
+
+# Copied from sre_compile.py in CPython 3.7.  Previously failed to detect variable initialisation.
+_equivalences = (
+    # LATIN SMALL LETTER I, LATIN SMALL LETTER DOTLESS I
+    (0x69, 0x131), # iı
+    # LATIN SMALL LETTER S, LATIN SMALL LETTER LONG S
+    (0x73, 0x17f), # sſ
+    # MICRO SIGN, GREEK SMALL LETTER MU
+    (0xb5, 0x3bc), # µμ
+    # COMBINING GREEK YPOGEGRAMMENI, GREEK SMALL LETTER IOTA, GREEK PROSGEGRAMMENI
+    (0x345, 0x3b9, 0x1fbe), # \u0345ιι
+    # ...
+)
+
+_ignorecase_fixes = {
+    i: tuple(j for j in t if i != j)
+    for t in _equivalences for i in t
+}
+
+def nested_tuple():
+    """
+    >>> modlevel, funclevel = nested_tuple()
+    >>> modlevel == funclevel or (modlevel, funclevel)
+    True
+    """
+    inner_ignorecase_fixes = {
+        i: tuple(j for j in t if i != j)
+        for t in _equivalences for i in t
+    }
+
+    return sorted(_ignorecase_fixes.items()), sorted(inner_ignorecase_fixes.items())