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Diagnose explicit Self in extend in the parse node handler (Refactor Impl construction 1/7) (#6465)

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We encode the state of looking that the parent scope is a Class into a
type so that we can avoid extra lookups. Then use that in refactoring
where diagnostics are generated for an explicit `Self` in an `extend
impl` declaration.

We add tests that we don't double-diagnose the Self type when it's
already an error, and make the behaviour of `extend require` match that
of `extend impl as`.

This avoids some fragile/complex parse-node lookups (such as
`context.parse_tree_and_subtrees().ExtractAs<Parse::ImplTypeAs>`) by
using the parse node at the point where we are handling it instead of
much later.

This is part of #6420 which is being split up into a chain of smaller
PRs.
This commit is contained in:
Dana Jansens
2025-12-09 20:38:50 +00:00
committed by GitHub
parent 154e4012c4
commit 2d38978756
10 changed files with 160 additions and 61 deletions
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toolchain/check/impl.cpp
+1 -41
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@@ -399,24 +399,10 @@ static auto TryAsClassScope(Context& context, SemIR::NameScopeId scope_id)
return context.insts().TryGetAs<SemIR::ClassDecl>(scope.inst_id());
}
auto GetImplDefaultSelfType(Context& context) -> SemIR::TypeId {
auto parent_scope_id = context.decl_name_stack().PeekParentScopeId();
if (auto class_decl = TryAsClassScope(context, parent_scope_id)) {
return context.classes().Get(class_decl->class_id).self_type_id;
}
// TODO: This is also valid in a mixin.
return SemIR::TypeId::None;
}
// Process an `extend impl` declaration by extending the impl scope with the
// `impl`'s scope.
static auto ExtendImpl(Context& context, Parse::NodeId extend_node,
SemIR::LocId loc_id, SemIR::ImplId impl_id,
Parse::NodeId self_type_node_id,
SemIR::TypeId self_type_id,
SemIR::LocId implicit_params_loc_id,
SemIR::TypeInstId constraint_type_inst_id,
SemIR::TypeId constraint_type_id) -> bool {
@@ -443,31 +429,6 @@ static auto ExtendImpl(Context& context, Parse::NodeId extend_node,
const auto& impl = context.impls().Get(impl_id);
if (context.parse_tree().node_kind(self_type_node_id) ==
Parse::NodeKind::ImplTypeAs) {
CARBON_DIAGNOSTIC(ExtendImplSelfAs, Error,
"cannot `extend` an `impl` with an explicit self type");
auto diag = context.emitter().Build(extend_node, ExtendImplSelfAs);
// If the explicit self type is not the default, just bail out.
if (self_type_id != GetImplDefaultSelfType(context)) {
diag.Emit();
parent_scope.set_has_error();
return false;
}
// The explicit self type is the same as the default self type, so suggest
// removing it and recover as if it were not present.
if (auto self_as =
context.parse_tree_and_subtrees().ExtractAs<Parse::ImplTypeAs>(
self_type_node_id)) {
CARBON_DIAGNOSTIC(ExtendImplSelfAsDefault, Note,
"remove the explicit `Self` type here");
diag.Note(self_as->type_expr, ExtendImplSelfAsDefault);
}
diag.Emit();
}
if (impl.witness_id == SemIR::ErrorInst::InstId) {
parent_scope.set_has_error();
} else {
@@ -618,8 +579,7 @@ auto StartImplDecl(Context& context, SemIR::LocId loc_id,
stored_impl_info.generic_id)});
}
if (!ExtendImpl(context, extend_impl->extend_node_id, loc_id,
impl_decl.impl_id, extend_impl->self_type_node_id,
self_type_id, implicit_params_loc_id, constraint_id,
impl_decl.impl_id, implicit_params_loc_id, constraint_id,
extend_impl->constraint_type_id)) {
// Don't allow the invalid impl to be used.
FillImplWitnessWithErrors(context, stored_impl_info);