refactor: replace 27 positional-argument `infer/hir.rs` signatures with an inference context

[shunichironomura]

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Summary

27 functions in crates/graphcal-compiler/src/tir/dim_check/infer/hir.rs (5283 lines) carry #[expect(clippy::too_many_arguments, ...)], each threading the same ambient parameter bundle. The context struct that solves this already exists one directory up and is already used by two sibling modules — the infer/ submodule was simply never migrated.

Current shape

#[expect(clippy::too_many_arguments, reason = "mirrors syntax inference context")]
fn infer_hir_type(
    expr: &hir::Expr,
    owner_decl_name: Option<&ResolvedDeclName>,
    declared_types: &HashMap<ScopedName, DeclaredType>,
    local_types: &HirLocalTypes<'_>,
    dag: &crate::tir::typed::DagTIR,
    tir: &crate::tir::typed::TIR,
    registry: &SemanticRegistry,
    builtin_fns: &crate::registry::builtins::BuiltinFunctions,
    src: &NamedSource<Arc<String>>,
) -> Result<InferredType, GraphcalError>

The reason strings are themselves the tell: "mirrors syntax inference context", "mirrors infer_hir_type's signature". There is a context object; it just is not reified here.

Affected functions include infer_hir_type, infer_hir_type_inner, infer_arg, infer_hir_fn_call, infer_hir_binop, infer_hir_if, infer_hir_for_comp, infer_hir_index_access, infer_hir_field_access, infer_hir_constructor_call, infer_hir_scan, infer_hir_unfold, infer_hir_match, infer_hir_dag_call and others.

Mechanically, in this one file: 85 bare registry, threading lines and 69 bare builtin_fns, threading lines.

The remedy already exists

crates/graphcal-compiler/src/tir/dim_check/mod.rs:282:

/// Per-DAG context bundle threaded through the dimension-check passes.
///
/// Bundles the read-only inputs that every per-declaration check needs
/// (declared types, the locals scope, TIR, registry, builtins, source)
/// so individual helpers take a single `&DimCheckContext` instead of
/// six positional arguments.
#[derive(Clone, Copy)]
struct DimCheckContext<'a> {
    cancellation: &'a crate::cancellation::CancellationToken,
    materialized_shapes: &'a infer::hir::MaterializedShapeCollector,
    declared_types: &'a HashMap<ScopedName, DeclaredType>,
    dag: Option<&'a crate::tir::typed::DagTIR>,
    tir: &'a crate::tir::typed::TIR,
    registry: &'a SemanticRegistry,
    builtin_fns: &'a crate::registry::builtins::BuiltinFunctions,
    src: &'a NamedSource<Arc<String>>,
}

It is already used by dim_check/mod.rs and dim_check/plot.rs.

Suggested fix

Introduce an InferCtx<'a> (or reuse/extend DimCheckContext) carrying the invariant fields, leaving only the genuinely varying arguments (expr, local_types, owner_decl_name) positional.

Expected effect: ~27 #[expect] attributes and several hundred argument-threading lines removed from the largest non-test file in the compiler.

Sequencing note

This is the largest diff of the review's findings and touches the file most likely to conflict with other in-flight work. Worth landing alone, on its own branch, with no behavioural change — the 2926-test suite is the oracle.

Provenance

Found during a full-workspace code review at 6e462341a (v0.0.1-alpha.27). Baseline at that commit: cargo clippy --workspace --all-targets clean, cargo test --workspace 2926 passed / 0 failed, cargo deny check advisories ok.