extend<record T: {...}> T: Aspect is accepted, then never applies

LIMIT-COHERENCE-001

A blanket aspect impl bounded by a row (extend<record T: { x: f64, .. }> T: A) passes coherence, but a call through the bound never dispatches to it; the same class of mistake is rejected outright for the equivalent non-generic form.

Lifecycle

known

Owner

metel-frontend

Scope

architecture/spec/coherence.md#coherence

Origin

metel-core#1241

Affects · linked records

spec.declarations.aspects.aspect-implementation-coherence.legality-1language spec rule

metel-frontend/src/pipeline/coherence/mod.rscode path

limitationKnown limitations ↗

Limitation

Reproduced against current develop:

aspect A { fun f(self) -> i64; }
extend<record T: { x: f64, .. }> T: A { fun f(self) -> i64 { 1 } }
fun main() {
    let r := { x = 1.0, y = 2.0 };
    println(r.f().to_string());
}

Coherence accepts the extend. The call fails: [T0002] type error: cannot infer receiver type for method call; add a type annotation — the impl is never found. The direct, non-generic form of the same mistake (extend { x: f64 }: A { … }) is rejected outright since metel-core#239, with a clear message ("cannot extend an anonymous record type"). This generic, row-bounded form slips through the same class of check.

This is a different case from GAP-DECLARATIONS-001 (no local aspect impl for a tuple or anonymous record target) and GAP-TYPES-004 (extend<row R> does not parse at all): here the extend uses the ordinary, already-supported record T: { .. } bound and is accepted, then silently does nothing.

Impact

The extend declares an impl that silently has no effect; the program compiles and then fails at the call site with a diagnostic that does not name the real cause.

Affects

• spec.declarations.aspects.aspect-implementation-coherence.legality-1
• metel-frontend/src/pipeline/coherence/mod.rs

Resolution

None yet; tracked as metel-core#1241. Either the impl is made to apply, or (matching metel-core#239's precedent) the extend is rejected at the declaration site with a message naming the real cause.