[mypyc] Remangle names produced by allow-redefinition (#11175)

Fixes mypyc/mypyc#702 by replacing "'" with "__redef__",
although this assumes nothing else will ever use demangling
for now.

Only locals need any fix; a run testcase was added to verify
that it works already for globals, and since the fix for locals
is on the ir level only an ir testcase is added.

Author: jhance

mypyc/irbuild/builder.py

@@ -1066,7 +1066,12 @@ def add_local(self, symbol: SymbolNode, typ: RType, is_arg: bool = False) -> 'Re
             is_arg: is this a function argument
         """
         assert isinstance(symbol, SymbolNode)
-        reg = Register(typ, symbol.name, is_arg=is_arg, line=symbol.line)
+        reg = Register(
+            typ,
+            remangle_redefinition_name(symbol.name),
+            is_arg=is_arg,
+            line=symbol.line,
+        )
         self.symtables[-1][symbol] = AssignmentTargetRegister(reg)
         if is_arg:
             self.builder.args.append(reg)
@@ -1203,3 +1208,14 @@ def get_default() -> Value:
                         GetAttr(builder.fn_info.callable_class.self_reg, name, arg.line))
             assert isinstance(target, AssignmentTargetRegister)
             builder.assign_if_null(target.register, get_default, arg.initializer.line)
+
+
+def remangle_redefinition_name(name: str) -> str:
+    """Remangle names produced by mypy when allow-redefinition is used and a name
+    is used with multiple types within a single block.
+
+    We only need to do this for locals, because the name is used as the name of the register;
+    for globals, the name itself is stored in a register for the purpose of doing dict
+    lookups.
+    """
+    return name.replace("'", "__redef__")

mypyc/test-data/irbuild-basic.test

@@ -3745,3 +3745,27 @@ L3:
     goto L1
 L4:
     return 1
+[case testLocalRedefinition]
+# mypy: allow-redefinition
+def f() -> None:
+    i = 0
+    i += 1
+    i = "foo"
+    i += i
+    i = 0.0
+[out]
+def f():
+    i, r0 :: int
+    r1, i__redef__, r2 :: str
+    r3, i__redef____redef__ :: float
+L0:
+    i = 0
+    r0 = CPyTagged_Add(i, 2)
+    i = r0
+    r1 = 'foo'
+    i__redef__ = r1
+    r2 = CPyStr_Append(i__redef__, i__redef__)
+    i__redef__ = r2
+    r3 = 0.0
+    i__redef____redef__ = r3
+    return 1

mypyc/test-data/run-misc.test

@@ -1089,3 +1089,14 @@ class A:
 class B(A):
     def _(arg): pass
     def _(arg): pass
+
+[case testGlobalRedefinition_toplevel]
+# mypy: allow-redefinition
+i = 0
+i += 1
+i = "foo"
+i += i
+i = b"foo"
+
+def test_redefinition() -> None:
+    assert i == b"foo"