✨ feat: add type predicate-based narrowing for union types in if/elif branches#1367
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✨ feat: add type predicate-based narrowing for union types in if/elif branches#1367
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harehare
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Mar 1, 2026
harehare
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- Implements ConditionNarrowings and TypeNarrowing tracking in constraint generation
- Applies narrowed types to Ref symbols in then/else branches after unification
- Supports is_string, is_number, is_bool, is_none, is_array, is_dict predicates
- Handles negation, logical AND/OR, and compound conditions
- Adds integration tests for type narrowing behavior
…pes in if/elif branches - Implements ConditionNarrowings and TypeNarrowing tracking in constraint generation - Applies narrowed types to Ref symbols in then/else branches after unification - Supports is_string, is_number, is_bool, is_none, is_array, is_dict predicates - Handles negation, logical AND/OR, and compound conditions - Adds integration tests for type narrowing behavior
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Pull request overview
Adds type predicate-based narrowing to mq-typechecker so union-typed variables can be treated as more specific types within if/elif branch scopes after unification, enabling better operator/builtin checking behind runtime guards.
Changes:
- Track predicate-derived narrowings during constraint generation and apply them post-unification to
Refsymbols within branch subtrees. - Introduce
TypeNarrowing/NarrowingEntrystorage in the inference context and addType::subtractto compute complement types. - Add integration tests exercising basic narrowing scenarios (predicates, negation,
&&, and union narrowing across branches).
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.
Show a summary per file
| File | Description |
|---|---|
| crates/mq-typechecker/src/constraint.rs | Extracts predicate narrowings from condition expressions and records them for later application. |
| crates/mq-typechecker/src/infer.rs | Adds data structures and context plumbing to store collected narrowings. |
| crates/mq-typechecker/src/lib.rs | Applies recorded narrowings post-unification by overriding Ref symbol types in branch scopes. |
| crates/mq-typechecker/src/types.rs | Adds Type::subtract to compute complement types for union narrowing. |
| crates/mq-typechecker/tests/integration_test.rs | Adds integration tests for the narrowing behavior. |
…nd match patterns
…narrowing analysis
…and improve error handling
… builtin preloading
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