From 70fa9845a17b308fa5b9b88b9befa5243a3c7ef3 Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Thu, 2 Oct 2025 02:27:18 -0400
Subject: [PATCH 1/3] [mypyc] feat: add CastExpr support to
 `constant_fold_expr`

---
 mypy/constant_fold.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mypy/constant_fold.py b/mypy/constant_fold.py
index 4582b2a7396d..7709debb4f57 100644
--- a/mypy/constant_fold.py
+++ b/mypy/constant_fold.py
@@ -8,6 +8,7 @@
 from typing import Final, Union
 
 from mypy.nodes import (
+    CastExpr,
     ComplexExpr,
     Expression,
     FloatExpr,
@@ -73,6 +74,8 @@ def constant_fold_expr(expr: Expression, cur_mod_id: str) -> ConstantValue | Non
         value = constant_fold_expr(expr.expr, cur_mod_id)
         if value is not None:
             return constant_fold_unary_op(expr.op, value)
+    elif isinstance(expr, CastExpr):
+        return constant_fold_expr(expr.expr, cur_mod_id)
     return None
 
 

From 2d177e973ec31be9daf873b76454460feafdf668 Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Thu, 2 Oct 2025 02:29:57 -0400
Subject: [PATCH 2/3] Update constant_fold.py

---
 mypyc/irbuild/constant_fold.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mypyc/irbuild/constant_fold.py b/mypyc/irbuild/constant_fold.py
index 12a4b15dd40c..73eb5777cbeb 100644
--- a/mypyc/irbuild/constant_fold.py
+++ b/mypyc/irbuild/constant_fold.py
@@ -15,6 +15,7 @@
 from mypy.constant_fold import constant_fold_binary_op, constant_fold_unary_op
 from mypy.nodes import (
     BytesExpr,
+    CastExpr,
     ComplexExpr,
     Expression,
     FloatExpr,
@@ -72,6 +73,8 @@ def constant_fold_expr(builder: IRBuilder, expr: Expression) -> ConstantValue |
         value = constant_fold_expr(builder, expr.expr)
         if value is not None and not isinstance(value, bytes):
             return constant_fold_unary_op(expr.op, value)
+    elif isinstance(expr, CastExpr):
+        return constant_fold_expr(builder, expr.expr)
     return None
 
 

From a8f50cef0eb899217083db83ece1506506337f78 Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Fri, 3 Oct 2025 17:44:42 -0400
Subject: [PATCH 3/3] Update expression.py

---
 mypyc/irbuild/expression.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mypyc/irbuild/expression.py b/mypyc/irbuild/expression.py
index 59ecc4ac2c5c..7d278a3bee02 100644
--- a/mypyc/irbuild/expression.py
+++ b/mypyc/irbuild/expression.py
@@ -518,6 +518,7 @@ def translate_super_method_call(builder: IRBuilder, expr: CallExpr, callee: Supe
     return builder.builder.call(decl, arg_values, arg_kinds, arg_names, expr.line)
 
 
+@folding_candidate
 def translate_cast_expr(builder: IRBuilder, expr: CastExpr) -> Value:
     src = builder.accept(expr.expr)
     target_type = builder.type_to_rtype(expr.type)