[mypyc] feat: add IndexOp support to constant_fold_expr

Author: BobTheBuidler

mypyc/irbuild/constant_fold.py

@@ -72,6 +72,15 @@ 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, IndexOp):
+        base = constant_fold_expr(builder, expr.base)
+        if base is not None:
+            index = constant_fold_expr(builder, expr.base)
+            if index is not None:
+                try:
+                    return base[index]
+                except Exception:
+                    return None
     return None