Lower twill-parser's borrowed AST to an owned/interned tree

jacksonopp commented

2026-08-20 19:06:07 +00:00

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twill-parser's Expr<'src> is zero-copy, borrowing from the source &str. Salsa's tracked-struct outputs need to be cheaply Eq/hashable for early-cutoff, and threading twill-parser's 'src lifetime through salsa's 'db-bound tracked structs fights the framework for no benefit.

Decided in #1's discussion: immediately after parsing, lower the borrowed Spanned<Expr<'src>> into an owned tree, and intern identifiers as a Symbol type (via salsa::interned) from the start rather than starting with plain owned Strings. Reasoning: interned symbols give stable identity across revisions, which is what makes structural Eq on the lowered tree actually early-cutoff unrelated queries, and Step 2's type checker will want Symbol-shaped identifiers for the symbol table anyway -- deferring interning just means redoing this once Step 2 lands.

Scope: define the lowering module/pass and the Symbol interned type; everything else in the lowered tree stays plain owned data for now.

twill-parser's Expr<'src> is zero-copy, borrowing from the source &str. Salsa's tracked-struct outputs need to be cheaply Eq/hashable for early-cutoff, and threading twill-parser's 'src lifetime through salsa's 'db-bound tracked structs fights the framework for no benefit. Decided in #1's discussion: immediately after parsing, lower the borrowed Spanned<Expr<'src>> into an owned tree, and intern identifiers as a Symbol type (via salsa::interned) from the start rather than starting with plain owned Strings. Reasoning: interned symbols give stable identity across revisions, which is what makes structural Eq on the lowered tree actually early-cutoff unrelated queries, and Step 2's type checker will want Symbol-shaped identifiers for the symbol table anyway -- deferring interning just means redoing this once Step 2 lands. Scope: define the lowering module/pass and the Symbol interned type; everything else in the lowered tree stays plain owned data for now.

jacksonopp added this to the Step 2: Core Type Checker milestone

2026-08-20 19:06:07 +00:00

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2026-08-20 19:06:07 +00:00

jacksonopp referenced this issue

2026-08-20 19:06:17 +00:00

Design the checker crate skeleton (crates/twill-check) #1

jacksonopp added this to the twill project

2026-08-20 19:06:38 +00:00

jacksonopp referenced this issue