From fbc9e5031d1ef1a8bd6572485f099ce918110aa2 Mon Sep 17 00:00:00 2001
From: Jeong YunWon <jeong@youknowone.org>
Date: Sun, 29 Jun 2025 04:10:51 +0900
Subject: [PATCH] Fix TypeParams, TypeAlias compile

---
 compiler/codegen/src/compile.rs | 26 ++++++++++++++++++++++----
 vm/src/frame.rs                 | 16 ++++++++++++----
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/compiler/codegen/src/compile.rs b/compiler/codegen/src/compile.rs
index 2e7e5a4ad5..71b94cdb96 100644
--- a/compiler/codegen/src/compile.rs
+++ b/compiler/codegen/src/compile.rs
@@ -1042,14 +1042,32 @@ impl Compiler<'_> {
                     )));
                 };
                 let name_string = name.id.to_string();
-                if type_params.is_some() {
-                    self.push_symbol_table();
-                }
-                self.compile_expression(value)?;
+
+                // For PEP 695 syntax, we need to compile type_params first
+                // so that they're available when compiling the value expression
                 if let Some(type_params) = type_params {
+                    self.push_symbol_table();
+
+                    // Compile type params first to define T1, T2, etc.
                     self.compile_type_params(type_params)?;
+                    // Stack now has type_params tuple at top
+
+                    // Compile value expression (can now see T1, T2)
+                    self.compile_expression(value)?;
+                    // Stack: [type_params_tuple, value]
+
+                    // We need [value, type_params_tuple] for TypeAlias instruction
+                    emit!(self, Instruction::Rotate2);
+
                     self.pop_symbol_table();
+                } else {
+                    // No type params - push value first, then None (not empty tuple)
+                    self.compile_expression(value)?;
+                    // Push None for type_params (matching CPython)
+                    self.emit_load_const(ConstantData::None);
                 }
+
+                // Push name last
                 self.emit_load_const(ConstantData::Str {
                     value: name_string.clone().into(),
                 });
diff --git a/vm/src/frame.rs b/vm/src/frame.rs
index 7f10a348f2..3a02d582a1 100644
--- a/vm/src/frame.rs
+++ b/vm/src/frame.rs
@@ -1266,10 +1266,18 @@ impl ExecutingFrame<'_> {
             }
             bytecode::Instruction::TypeAlias => {
                 let name = self.pop_value();
-                let type_params: PyTupleRef = self
-                    .pop_value()
-                    .downcast()
-                    .map_err(|_| vm.new_type_error("Type params must be a tuple."))?;
+                let type_params_obj = self.pop_value();
+
+                // CPython allows None or tuple for type_params
+                let type_params: PyTupleRef = if vm.is_none(&type_params_obj) {
+                    // If None, use empty tuple (matching CPython's behavior)
+                    vm.ctx.empty_tuple.clone()
+                } else {
+                    type_params_obj
+                        .downcast()
+                        .map_err(|_| vm.new_type_error("Type params must be a tuple."))?
+                };
+
                 let value = self.pop_value();
                 let type_alias = typing::TypeAliasType::new(name, type_params, value);
                 self.push_value(type_alias.into_ref(&vm.ctx).into());