[mypyc] Remangle redefined names produced by async with (#16408)

Fixes mypyc/mypyc#1001.

---------

Co-authored-by: Jelle Zijlstra <[email protected]>

Author: ichard26

mypyc/irbuild/builder.py

@@ -1246,14 +1246,15 @@ def add_var_to_env_class(
     ) -> AssignmentTarget:
         # First, define the variable name as an attribute of the environment class, and then
         # construct a target for that attribute.
-        self.fn_info.env_class.attributes[var.name] = rtype
-        attr_target = AssignmentTargetAttr(base.curr_env_reg, var.name)
+        name = remangle_redefinition_name(var.name)
+        self.fn_info.env_class.attributes[name] = rtype
+        attr_target = AssignmentTargetAttr(base.curr_env_reg, name)
 
         if reassign:
             # Read the local definition of the variable, and set the corresponding attribute of
             # the environment class' variable to be that value.
             reg = self.read(self.lookup(var), self.fn_info.fitem.line)
-            self.add(SetAttr(base.curr_env_reg, var.name, reg, self.fn_info.fitem.line))
+            self.add(SetAttr(base.curr_env_reg, name, reg, self.fn_info.fitem.line))
 
         # Override the local definition of the variable to instead point at the variable in
         # the environment class.

mypyc/test-data/run-async.test

@@ -143,3 +143,31 @@ async def foo() -> AsyncIterable[int]:
 yields, val = run_generator(async_iter(foo()))
 assert yields == (0,1,2), yields
 assert val == 'lol no', val
+
+[case testAsyncWithVarReuse]
+class ConMan:
+    async def __aenter__(self) -> int:
+        return 1
+    async def __aexit__(self, *exc: object):
+        pass
+
+class ConManB:
+    async def __aenter__(self) -> int:
+        return 2
+    async def __aexit__(self, *exc: object):
+        pass
+
+async def x() -> None:
+    value = 2
+    async with ConMan() as f:
+        value += f
+    assert value == 3, value
+    async with ConManB() as f:
+        value += f
+    assert value == 5, value
+
+[typing fixtures/typing-full.pyi]
+[file driver.py]
+import asyncio
+import native
+asyncio.run(native.x())