[mypyc] Fix name lookup when class var and module var have the same name (#21594)

Disambiguate using the Var node, since the short name itself is not
enough to disambiguate between global variable and class variable
with the same name.

Fixes mypyc/mypyc#1201.

Author: JukkaL

mypyc/irbuild/builder.py

@@ -251,11 +251,11 @@ def __init__(
 
         self.visitor = visitor
 
-        # Class body context: tracks ClassVar names defined so far when processing
+        # Class body context: tracks ClassVars defined so far when processing
         # a class body, so that intra-class references (e.g. C = A | B where A is
         # a ClassVar defined earlier in the same class) can be resolved correctly.
         # Without this, mypyc looks up such names in module globals, which fails.
-        self.class_body_classvars: dict[str, None] = {}
+        self.class_body_classvars: dict[Var, None] = {}
         self.class_body_obj: Value | None = None
         self.class_body_ir: ClassIR | None = None
 

mypyc/irbuild/classdef.py

@@ -26,6 +26,7 @@
     TempNode,
     TypeInfo,
     TypeParam,
+    Var,
     is_class_var,
 )
 from mypy.types import Instance, UnboundType, get_proper_type
@@ -186,7 +187,8 @@ def transform_class_def(builder: IRBuilder, cdef: ClassDef) -> None:
             cls_builder.add_attr(lvalue, stmt)
             # Track this ClassVar so subsequent class body statements can reference it.
             if is_class_var(lvalue) or stmt.is_final_def:
-                builder.class_body_classvars[lvalue.name] = None
+                assert isinstance(lvalue.node, Var), lvalue.node
+                builder.class_body_classvars[lvalue.node] = None
 
         elif isinstance(stmt, ExpressionStmt) and isinstance(stmt.expr, StrExpr):
             # Docstring. Ignore

mypyc/irbuild/expression.py

@@ -232,7 +232,11 @@ def transform_name_expr(builder: IRBuilder, expr: NameExpr) -> Value:
     # If we're evaluating a class body and this name is a ClassVar defined earlier
     # in the same class, load it from the class being built (type object for ext classes,
     # class dict for non-ext classes) instead of module globals.
-    if builder.class_body_obj is not None and expr.name in builder.class_body_classvars:
+    if (
+        builder.class_body_obj is not None
+        and isinstance(expr.node, Var)
+        and expr.node in builder.class_body_classvars
+    ):
         if builder.class_body_ir is not None and builder.class_body_ir.is_ext_class:
             return builder.py_get_attr(builder.class_body_obj, expr.name, expr.line)
         else:

mypyc/test-data/run-classes.test

@@ -1113,6 +1113,24 @@ assert f() == 10
 A.x = 200
 assert f() == 200
 
+[case testClassVarDoesNotShadowMethodGlobal]
+from typing import ClassVar
+from testutil import assertRaises
+
+class E(Exception):
+    pass
+
+class C:
+    E: ClassVar[type[E]] = E
+
+    def m(self, b: bytes) -> None:
+        if not b:
+            raise E()
+
+def test_class_var_does_not_shadow_method_global() -> None:
+    with assertRaises(E):
+        C().m(b"")
+
 [case testInitSubclassWithClassVar]
 from typing import ClassVar