feat(syntax,semantic,lowering): support tuple struct syntax (struct Foo(T1, T2))

[orizi]

Summary

Adds support for tuple struct syntax in Cairo, allowing structs to be defined with positional, unnamed fields using parentheses: struct Foo(pub u32, u64). This introduces a new StructBody enum in the AST with two variants — StructBodyBraces (the existing { field: Type } form) and StructBodyParens (the new (Type, Type) form) — replacing the flat lbrace/members/rbrace fields on ItemStruct.

New AST nodes StructArgMember, StructArgMemberList, StructBodyBraces, and StructBodyParens are added to the syntax spec and generated code. The parser is extended to detect a leading ( after the struct name and parse a StructArgMemberList instead of a MemberList.

On the semantic side, StructDefinitionData gains a positional_tys field (a Vec<(TypeId, Visibility)>) populated for tuple structs. Two new Salsa queries — struct_positional_types and concrete_struct_positional_types — expose these types with generic substitution applied. type_members is updated to return TupleElement-kinded members (keyed by stringified index, e.g. "0", "1") for tuple structs, enabling member access expressions like p.0.

Lowering is updated so that TupleElement access on a concrete struct type fetches positional types via concrete_struct_positional_types rather than assuming the container is always a TypeLongId::Tuple.

The MemberId::struct_id parent pointer traversal is corrected from 2 levels to 3 levels up to account for the new StructBodyBraces intermediate node.

All call sites that previously called struct_ast.members(db) directly are updated to first match on StructBody::Braces, gracefully skipping or returning early for tuple structs.

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Type of change

Please check one:

• Bug fix (fixes incorrect behavior)
• New feature
• Performance improvement
• Documentation change with concrete technical impact
• Style, wording, formatting, or typo-only change

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Why is this change needed?

Cairo previously only supported braced struct syntax. Tuple structs (positional, unnamed fields) are a common pattern in Rust-like languages and are needed to support use cases where field names are unnecessary or where struct types should behave similarly to tuples with named types.

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What was the behavior or documentation before?

Structs could only be declared with named fields inside braces: struct Foo { x: u32, y: u64 }. The ItemStruct AST node directly held lbrace, members, and rbrace children.

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What is the behavior or documentation after?

Structs can additionally be declared with positional fields inside parentheses: struct Foo(pub u32, u64). Fields are accessed by numeric index (e.g., foo.0). The ItemStruct AST node now holds a single body child of type StructBody, which is either StructBodyBraces or StructBodyParens.

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Related issue or discussion (if any)

N/A

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Additional context

Parser test data snapshots (test1, test2, attrs) are updated to reflect the new StructBodyBraces wrapper node in the AST. A new unit test test_tuple_struct verifies positional type extraction, visibility, and type_members behavior for tuple structs.

[reviewable-StarkWare]

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[orizi]

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• feat(syntax,semantic,lowering): support tuple struct syntax (struct Foo(T1, T2)) #9885 👈 (View in Graphite)
• feat(semantic): support tuple member access via v.0 syntax (#7608) #9884
• refactor(semantic): introduce TypeMember abstraction for unified struct/tuple member access #9883
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