RFC-0173 generic-body checking was incomplete
Limitation
RFC-0173 makes the definition-time check the contract for a generic body: each declared
parameter is rigid, and a use is allowed only if the declared bounds entail it. The completed
implementation (metel-core#1364) keeps row decompositions as symbolic facts through generic
calls and generalized schemes; checks direct and where all bound forwarding; makes
conditional-impl visibility depend on declared entailment; and records solver provenance so a
rigidity mismatch (T0001) points at the causal expression. A construction disagreement is
I0010, never a call-site type error. Operators on bare parameters remain the separate
language-level gap GAP-TYPES-005.
Impact
At the time, a generic function could over-constrain its parameters or use an entitlement that only a concrete caller supplied. Row-polymorphic code was affected most because a remainder could collapse into its source row. The completed implementation enforces the RFC-0173 contract at the definition.
Affects
spec.types.generics.rigid-type-parameters.legality-1spec.types.generics.rigid-type-parameters.legality-2spec.types.generics.rigid-type-parameters.dynamics-1
Resolution
Resolved by metel-core#1364 and ADR-0058. LIMIT-EVALUATION-001 (the per-call
reconstruction) remains a separate implementation boundary; its failure mode is guarded by
I0010 and the differential fixture sweep specified in ADR-0058.