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GeezerVison is showing github.com — Fix TypeParams, TypeAlias compile by youknowone · Pull Request #5862 · RustPython/RustPython

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@youknowone

@youknowone youknowone commented Jun 28, 2025 •
edited by coderabbitai Bot
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Summary by CodeRabbit

  • Bug Fixes
    • Improved handling of type aliases with optional type parameters, ensuring correct behavior and compatibility with PEP 695 and CPython standards.
    • Fixed stack order and processing for type aliases, allowing both None and tuple type parameters as valid inputs.

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@coderabbitai

coderabbitai Bot commented Jun 28, 2025 •
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Walkthrough

The changes update the compilation and execution of Python's TypeAlias statements to correctly support optional type parameters per PEP 695. The compiler now manages type parameter scoping and stack order, while the virtual machine's execution logic accepts either None or a tuple for type parameters, matching CPython's behavior.

Changes

File(s) Change Summary
compiler/codegen/src/compile.rs Refactored Stmt::TypeAlias compilation to handle optional type parameters and ensure correct stack order.
vm/src/frame.rs Updated TypeAlias instruction handling to accept None or tuple for type parameters, matching CPython.

Poem

In the warren where type aliases dwell,
Now with tuples or None, all is well.
The stack is in order, the scope is just right,
Type parameters hop in, no error in sight!
With PEP 695, we leap and we bound—
Hooray for the changes, so robust and sound! 🐇


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  • compiler/codegen/src/compile.rs (1 hunks)
  • vm/src/frame.rs (1 hunks)
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@youknowone youknowone changed the title Compatibility utilities Fix TypeParams, TypeAlias compil Jun 28, 2025
@youknowone youknowone changed the title Fix TypeParams, TypeAlias compil Fix TypeParams, TypeAlias compile Jun 28, 2025
coderabbitai[bot]
coderabbitai Bot reviewed Jun 28, 2025
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Actionable comments posted: 1

🧹 Nitpick comments (2)
vm/src/frame.rs (1)

1269-1280: Use PyTupleRef::try_from_object for a cleaner & more permissive tuple-conversion

The new None || tuple handling looks correct 👍.
You can remove the manual downcast boilerplate (and transparently accept tuple sub-classes, mirroring CPython) by leaning on the existing helper:

-    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 type_params: PyTupleRef = if vm.is_none(&type_params_obj) {
+        // If None, use the shared empty tuple (CPython behaviour)
+        vm.ctx.empty_tuple.clone()
+    } else {
+        PyTupleRef::try_from_object(vm, type_params_obj)?
+    };

This keeps semantics identical while reducing code and aligning the acceptance rules with CPython’s (i.e. tuple subclasses are valid).

compiler/codegen/src/compile.rs (1)

1031-1076: LGTM! Solid PEP 695 TypeAlias implementation with minor optimization opportunity.

The TypeAlias compilation logic correctly handles both cases:

  • With type parameters: Proper symbol table management, type params compiled first (making them available for value expression), and correct stack order via Rotate2
  • Without type parameters: Clean path that uses None instead of empty tuple for CPython compatibility

The stack manipulation logic is sound and the comments clearly explain the PEP 695 compliance requirements.

Minor optimization: Consider avoiding the extra string clone:

                let name_string = name.id.to_string();
-                self.emit_load_const(ConstantData::Str {
-                    value: name_string.clone().into(),
-                });
+                self.emit_load_const(ConstantData::Str {
+                    value: name_string.as_str().into(),
+                });
📜 Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 07a04ac and 5efda1b.

📒 Files selected for processing (10)
  • compiler/codegen/src/compile.rs (1 hunks)
  • vm/src/builtins/dict.rs (1 hunks)
  • vm/src/builtins/memory.rs (2 hunks)
  • vm/src/builtins/tuple.rs (0 hunks)
  • vm/src/builtins/type.rs (4 hunks)
  • vm/src/builtins/union.rs (3 hunks)
  • vm/src/exceptions.rs (1 hunks)
  • vm/src/frame.rs (1 hunks)
  • vm/src/protocol/object.rs (1 hunks)
  • vm/src/types/structseq.rs (1 hunks)
💤 Files with no reviewable changes (1)
  • vm/src/builtins/tuple.rs
🧰 Additional context used
🧠 Learnings (2)
vm/src/builtins/memory.rs (2)
Learnt from: CR
PR: RustPython/RustPython#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-06-26T12:52:11.138Z
Learning: Minimize modifications to CPython standard library files in the Lib/ directory; bug fixes should be made through Rust code modifications whenever possible.
Learnt from: CR
PR: RustPython/RustPython#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-06-26T12:52:11.138Z
Learning: Follow Rust best practices for error handling and memory management in all RustPython Rust code.
vm/src/builtins/type.rs (2)
Learnt from: CR
PR: RustPython/RustPython#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-06-26T12:52:11.138Z
Learning: Use the macro system (such as 'pyclass', 'pymodule', 'pyfunction') when implementing Python functionality in Rust for RustPython.
Learnt from: CR
PR: RustPython/RustPython#0
File: .github/copilot-instructions.md:0-0
Timestamp: 2025-06-26T12:52:11.138Z
Learning: When implementing a Python module in Rust for RustPython, use the #[pymodule] attribute and expose functions and classes using #[pyfunction], #[pyclass], and #[pymethod] as appropriate.
⏰ Context from checks skipped due to timeout of 90000ms (4)
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🔇 Additional comments (15)
vm/src/builtins/type.rs (6)

161-168: New utility function for MRO-based subtype checking looks good.

The is_subtype_with_mro function provides a clean way to check subtype relationships by iterating through the MRO. The implementation correctly uses reference equality with item.is(b).


209-213: Proper implementation of CPython's PyType_Check equivalent.

The check method correctly implements downcasting to check if an object is an instance of PyType (or its subclass), matching CPython's PyType_Check macro behavior.


457-459: Well-implemented subtype checking method.

The is_subtype method properly uses the new is_subtype_with_mro utility with the MRO read guard. The implementation is clean and follows Rust patterns.


461-465: Correct implementation of exact type checking.

The check_exact method properly implements CPython's PyType_CheckExact behavior using downcast_ref_if_exact, which ensures the object is exactly a PyType and not a subclass.


470-470: Minor cleanup in type signature.

Removing the fully qualified path crate:: from the type parameter is a good cleanup - the unqualified PyObject is clearer and more consistent.


1244-1248: Excellent improvement to avoid recursion in subclass checking.

The change to use subclass.real_is_subclass(self.as_object(), vm) instead of calling fast_issubclass directly is a significant improvement. This matches CPython's behavior by using _PyObject_RealIsSubclass and prevents potential infinite recursion through __subclasscheck__.

vm/src/types/structseq.rs (1)

100-100: Proper replacement of fast_getitem with direct indexing.

The change from zelf.fast_getitem(i.into()) to zelf[i as usize].to_owned() correctly follows the systematic removal of the fast_getitem method. Direct indexing is more idiomatic and the .to_owned() maintains the same ownership semantics.

vm/src/protocol/object.rs (1)

407-407: Correct replacement of fast_getitem with direct indexing.

The change from tuple.fast_getitem(0).clone() to tuple[0].clone() properly replaces the method call with direct indexing. This is part of the systematic removal of fast_getitem and maintains the same semantics.

vm/src/builtins/memory.rs (2)

213-219: LGTM: Safe direct indexing replacement

The replacement of fast_getitem with direct indexing x[0].to_owned() is correct and safe. The bounds check if x.len() == 1 ensures the indexing won't panic, and the semantics are preserved.


1068-1074: LGTM: Consistent refactoring pattern

Same safe replacement pattern as the unpack_single method. Direct indexing with proper bounds checking maintains correctness while improving performance and consistency.

vm/src/exceptions.rs (1)

1669-1671: LGTM: Safe tuple element access

The replacement of fast_getitem with direct indexing location_tuple[i].to_owned() is safe due to the bounds check if location_tup_len > i. This change maintains consistency with the broader codebase refactoring effort.

vm/src/builtins/dict.rs (1)

238-243: LGTM: Clean refactoring from fast_getitem to direct indexing.

The replacement of fast_getitem calls with direct tuple indexing is correct and maintains the same semantics. The tuple has already been validated to have length 2, making direct indexing safe.

vm/src/builtins/union.rs (3)

43-46: LGTM: Useful addition for internal access.

The new get_args method provides direct access to the internal args tuple, aligning with CPython's _Py_union_args attribute. This is a reasonable addition for internal VM use.


202-202: LGTM: Correct refactoring from fast_getitem to direct indexing.

The replacement of args.fast_getitem(0) with args[0].to_owned() is safe since this code path is only reached when args.len() == 1.


220-220: LGTM: Consistent tuple access pattern.

The change from new_args.fast_getitem(0) to new_args[0].to_owned() maintains the same semantics and is safe in this context where we know the tuple is non-empty.

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Comment thread vm/src/protocol/object.rs Resolved

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@youknowone
youknowone force-pushed the patches branch from 5efda1b to def2cdf Compare June 28, 2025 20:02
@youknowone
Fix TypeParams, TypeAlias compile
fbc9e50
@youknowone
youknowone force-pushed the patches branch from 6d30ff8 to fbc9e50 Compare June 28, 2025 20:08
@youknowone
youknowone merged commit 28dff8a into RustPython:main Jun 29, 2025
@youknowone
youknowone deleted the patches branch June 29, 2025 02:24
This was referenced Jul 1, 2025
__type_params__ in __build_class__ #5883
Merged
typing __parameters__ __type_params__ #5909
Merged
@coderabbitai coderabbitai Bot mentioned this pull request Jul 11, 2025
typing TypeAlias #5945
Merged
@coderabbitai coderabbitai Bot mentioned this pull request Oct 21, 2025
Use PyStrRef for TypeAliasType name #6203
Merged
@coderabbitai coderabbitai Bot mentioned this pull request Feb 9, 2026
Upgrade typing from 3.14.2 and more impl #7057
Merged
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