Walkthrough

The changes enhance the symbol table builder with context-aware error checking. New contextual state flags track whether expressions are processed within type parameters, annotations, type aliases, or inner comprehension loops. Error messages now reflect the precise context, and new validation logic prohibits named expressions in type parameters and detects inner-loop comprehension rebindings.

Changes

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• compile_type_param_bound_or_default #6005: Modifies scan_type_param_bound_or_default() and type-parameter-scoping logic, directly intersecting with this PR's type-parameter validation enhancements.
• Remove misplaced SymbolScope::TypeParams #5975: Modifies symbol table handling for type-parameter scopes and introduces context-aware error checks similar to this PR's approach.
• Refactor compile_function #6001: Modifies symbol table expression-scanning to restrict named expressions in type parameter scopes, aligning with this PR's validation goals.

Poem

🐰 A rabbit checks each context with care,
Named expressions forbidden in type-param air,
Comprehensions rebind? Not here, my friend!
With scope-aware errors, the mistakes we'll mend,
From bounds to defaults, precision's our way,
The symbol table grows wiser today!

Pre-merge checks and finishing touches

• 📝 Generate docstrings

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Reviewing files that changed from the base of the PR and between 37c47fc and 767c3e6.

• Lib/test/test_named_expressions.py is excluded by !Lib/**

• crates/codegen/src/symboltable.rs

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

**/*.rs: Follow the default rustfmt code style by running cargo fmt to format Rust code
Always run clippy to lint code (cargo clippy) before completing tasks and fix any warnings or lints introduced by changes
Follow Rust best practices for error handling and memory management
Use the macro system (pyclass, pymodule, pyfunction, etc.) when implementing Python functionality in Rust

Files:

• crates/codegen/src/symboltable.rs

crates/codegen/src/compile.rs (5)

• new (338-345)
• new (366-408)
• name (909-911)
• default (128-133)
• default (332-334)

crates/codegen/src/symboltable.rs (10)

588-592: LGTM!

The new error path correctly handles the case where a named expression in a comprehension is encountered within a type parameter scope. The error message aligns with CPython's behavior.

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624-631: LGTM!

The new state tracking fields are well-documented and appropriately typed. Using &'static str for scope_info is efficient for the string literal error message contexts.

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770-774: LGTM!

The save-and-restore pattern correctly handles nested annotations and properly restores the previous state after scanning.

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1043-1056: LGTM!

The in_type_alias flag is correctly scoped to the value expression only, not the name being defined. The save-and-restore pattern properly handles nested type aliases.

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1093-1126: LGTM!

The context-aware validation logic correctly prioritizes specific scope info over general context flags. The error messages are clear and include source locations for better diagnostics.

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1472-1477: LGTM!

The inner loop target tracking correctly identifies non-first generators in comprehensions.

Note: If scan_expression returns an error, in_comp_inner_loop_target won't be reset, but since errors propagate up and terminate symbol table building, this is acceptable.

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1501-1527: LGTM!

The function properly manages scope lifecycle with cleanup happening before returning the result, ensuring scope_info is restored and leave_scope is called even when scan_expression fails.

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1530-1548: LGTM!

The duplicate type parameter detection is correctly implemented with clear error messages and proper source locations.

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1567-1621: LGTM!

The scope naming and context info are well-structured, correctly distinguishing between TypeVar bounds vs. constraints based on tuple expressions, and providing meaningful scope names for each type parameter variant.

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1760-1775: LGTM!

The inner loop conflict check correctly implements PEP 572's restriction, preventing comprehension inner loops from rebinding variables that were previously used as named expression targets.

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