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Relax alias restrictions. (#7190)

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Implement the alias rules from proposal #5389, wherein an alias is
permitted so long as the target has a constant value. While that
proposal is not yet accepted, this seems like a reasonable basis for
further iteration, and will be useful for the examples we're currently
pursuing.
This commit is contained in:
Richard Smith
2026-05-12 17:22:44 +00:00
committed by GitHub
parent d4063cad65
commit dd7cfdb149
35 changed files with 262 additions and 219 deletions
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toolchain/check/handle_alias.cpp
+9 -22
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@@ -46,29 +46,16 @@ auto HandleParseNode(Context& context, Parse::AliasId /*node_id*/) -> bool {
{.name_id = name_context.name_id_for_new_inst(),
.parent_scope_id = name_context.parent_scope_id});
auto alias_type_id = SemIR::TypeId::None;
auto alias_value_id = SemIR::InstId::None;
if (auto inst = context.insts().TryGetAs<SemIR::NameRef>(expr_id)) {
// Pass through name references, albeit changing the name in use.
alias_type_id = inst->type_id;
alias_value_id = inst->value_id;
} else if (auto inst =
context.insts().TryGetAs<SemIR::TypeLiteral>(expr_id)) {
// Treat type literals such as `type` or `bool` like name references.
alias_type_id = inst->type_id;
alias_value_id = inst->value_id;
} else {
CARBON_DIAGNOSTIC(AliasRequiresNameRef, Error,
"alias initializer must be a name reference");
context.emitter().Emit(expr_node, AliasRequiresNameRef);
alias_type_id = SemIR::ErrorInst::TypeId;
alias_value_id = SemIR::ErrorInst::InstId;
if (!context.constant_values().Get(expr_id).is_constant()) {
CARBON_DIAGNOSTIC(AliasRequiresConstantValue, Error,
"alias refers to a runtime value");
context.emitter().Emit(expr_node, AliasRequiresConstantValue);
}
auto alias_id =
AddInst<SemIR::AliasBinding>(context, name_context.loc_id,
{.type_id = alias_type_id,
.entity_name_id = entity_name_id,
.value_id = alias_value_id});
auto alias_id = AddInst<SemIR::AliasBinding>(
context, name_context.loc_id,
{.type_id = context.insts().Get(expr_id).type_id(),
.entity_name_id = entity_name_id,
.value_id = expr_id});
// Add the name of the binding to the current scope.
context.decl_name_stack().PopScope();