Type-check primitives, let/var bindings, and blocks #48

Merged

jacksonopp merged 3 commits from us/2-type-check-primitives-let-var-blocks into main

2026-08-31 20:36:33 +00:00

jacksonopp commented

2026-08-27 02:50:44 +00:00

Owner

Closes #2.

Summary

Adds crates/twill-check/src/ty.rs: Ty (unsized primitive types), Scope
(a stack of frames for let/var binding and lexical shadowing), and the
checker walk (resolve_type_expr, check_let, check_expr, check_stmt).
Resolves TypeExpr::Named for the five primitives (Int/Float/Bool/
String/Unit); other TypeExpr variants are recognized but not yet
resolvable, reported as "not supported yet" rather than "unknown".
Checks let/var bindings: annotation vs. inferred-value mismatches,
redeclaration within the same block, and undefined-variable lookups.
Types Expr::Block Rust-style: the trailing expression's type (checked
while its own frame is still active, so it can see the block's own
bindings), or Ty::Unit if there's no trailing expression.
DiagnosticKind on diagnostic.rs's Diagnostic gives every diagnostic
structured data (Ty/Symbol/TypeExpr payloads) alongside a rendered
message, instead of ad hoc strings.
Wires a new #[salsa::tracked] check(db, file) -> Vec<Diagnostic> query
into queries.rs, alongside the existing lower query.
docs/type-checker-design.md: records the design decisions made along the
way (scope representation, diagnostic shape, query plumbing, etc.) per its
own living-doc convention.

Test plan

cargo test -p twill-check - 101 tests passing, including new unit
tests for Scope/resolve_type_expr/check_expr/check_let in ty.rs, and
end-to-end tests against check() in queries.rs (valid bindings,
mismatches, redeclaration, undefined variables, block
scoping/trailing-type behavior).

Closes #2. ## Summary - Adds `crates/twill-check/src/ty.rs`: `Ty` (unsized primitive types), `Scope` (a stack of frames for let/var binding and lexical shadowing), and the checker walk (`resolve_type_expr`, `check_let`, `check_expr`, `check_stmt`). - Resolves `TypeExpr::Named` for the five primitives (`Int`/`Float`/`Bool`/ `String`/`Unit`); other `TypeExpr` variants are recognized but not yet resolvable, reported as "not supported yet" rather than "unknown". - Checks `let`/`var` bindings: annotation vs. inferred-value mismatches, redeclaration within the same block, and undefined-variable lookups. - Types `Expr::Block` Rust-style: the trailing expression's type (checked while its own frame is still active, so it can see the block's own bindings), or `Ty::Unit` if there's no trailing expression. - `DiagnosticKind` on `diagnostic.rs`'s `Diagnostic` gives every diagnostic structured data (`Ty`/`Symbol`/`TypeExpr` payloads) alongside a rendered message, instead of ad hoc strings. - Wires a new `#[salsa::tracked] check(db, file) -> Vec<Diagnostic>` query into `queries.rs`, alongside the existing `lower` query. - `docs/type-checker-design.md`: records the design decisions made along the way (scope representation, diagnostic shape, query plumbing, etc.) per its own living-doc convention. ## Test plan - [x] `cargo test -p twill-check` - 101 tests passing, including new unit tests for Scope/resolve_type_expr/check_expr/check_let in ty.rs, and end-to-end tests against check() in queries.rs (valid bindings, mismatches, redeclaration, undefined variables, block scoping/trailing-type behavior).

jacksonopp added 3 commits

2026-08-27 02:50:44 +00:00