fix(typecheck): accept intersections in class assignments

[lewis6991]

• allow intersection types to be checked against class refs
• add tests for intersection<->class assignment behavior
• update intersection docs (EN/CN) and overload docs
• keep annotation tests aligned with intersection semantics

[gemini-code-assist]

Summary of Changes

Hello @lewis6991, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the type analysis capabilities by enabling the type checker to properly handle assignments involving intersection types and class definitions. It ensures that complex type compositions, where properties from multiple types are merged, are correctly validated against class structures, leading to more robust and accurate type inference.

Highlights

• Enhanced Type Checking for Intersections: The type checker now correctly processes intersection types when assigned to or from class references, improving the accuracy of type analysis.
• New Test Cases: Comprehensive tests have been added to validate the behavior of intersection type assignments, including property merging and policy-based overwrites.
• Updated Documentation: The English and Chinese documentation for intersection types has been expanded to clarify their order-sensitive nature and field conflict resolution.
• Code Refactoring: Introduced an intersection_to_object utility and integrated it into the type checking logic for LuaType::Def, LuaType::Ref, and LuaType::Intersection cases.

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Changelog

• crates/emmylua_code_analysis/src/compilation/test/annotation_test.rs
  • Added test_merge_right_mapped_type to verify property merging in intersection types.
  • Added test_extend_with_policy_overwrite to test explicit policy-based property overwrites in intersection types.
• crates/emmylua_code_analysis/src/diagnostic/test/assign_type_mismatch_test.rs
  • Introduced test_intersection_assign_to_class to check type mismatch when assigning an intersection to a class.
  • Introduced test_intersection_assign_from_class to check type mismatch when assigning a class to an intersection.
• crates/emmylua_code_analysis/src/semantic/type_check/complex_type/intersection_type_check.rs
  • Modified check_intersection_type_compact to convert LuaType::Def and LuaType::Ref intersection components into object types for type checking.
  • Imported intersection_to_object utility.
• crates/emmylua_code_analysis/src/semantic/type_check/mod.rs
  • Added intersection_utils module.
• crates/emmylua_code_analysis/src/semantic/type_check/ref_type.rs
  • Updated check_ref_class to handle LuaType::Intersection by converting it to an object type for comparison.
  • Imported intersection_to_object utility.
• docs/emmylua_doc/annotations_CN/type.md
  • Added detailed explanation for intersection types, including order sensitivity and field conflict resolution.
• docs/emmylua_doc/annotations_EN/overload.md
  • Minor formatting adjustment (added a blank line).
• docs/emmylua_doc/annotations_EN/type.md
  • Added detailed explanation for intersection types, including order sensitivity and field conflict resolution.

Activity

• The pull request was opened by lewis6991 with a clear description outlining the intent to allow intersection types to be checked against class references, add relevant tests, and update documentation.

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[gemini-code-assist]

Code Review

This pull request successfully implements type checking for assignments involving intersection types and class references. The changes are well-supported by new tests that cover various scenarios, including property overwriting based on intersection order. The documentation for intersection types has also been updated in both English and Chinese, which is a great addition for users. The core logic changes in intersection_type_check.rs and ref_type.rs correctly handle the conversion of intersection types to object types for comparison. I have one suggestion to improve code style for consistency. Overall, this is a great enhancement.

[gemini-code-assist]

For better readability and consistency with idiomatic Rust, you can refactor this if block to be an expression. This avoids the explicit return and makes the code flow similar to the new logic in ref_type.rs.

            if let Some(object_type) = intersection_to_object(context.db, source_intersection) {
                let object_type = LuaType::Object(Arc::new(object_type));
                check_general_type_compact(
                    context,
                    &object_type,
                    compact_type,
                    check_guard.next_level()?,
                )
            } else {
                Err(TypeCheckFailReason::TypeNotMatch)
            }

[xuhuanzy]

You should install the Git hooks first. The hooks include some basic checks to prevent failures in basic GitHub Actions checks.

Also, regarding AI usage, I recommend using gpt-5.2 in Codex (don’t use gpt-5.2-codex), with the reasoning effort set to xhigh. For backend work, Codex’s capabilities far exceed CC.

[lewis6991]

Ah ok, I have been using gpt-5.2-codex. I'll try gpt-5.2.

[xuhuanzy]

gpt-5.2-codex trades quality for speed, and its output quality is very poor. It should only be used for asking questions, not for generating code.

[xuhuanzy]

You can use gpt-5.2 to improve the previous PR.

From what I’ve seen, code generated by gpt-5.2 is usually two tiers better than gpt-5.2-codex, and most importantly, it tends to take edge cases into account.

[lewis6991]

The previous PR already handles some pretty whacky edge cases (with tests). I can try though.