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Explorer: move subtyping logic to TypeChecker (#2484)

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Addresses comments from this discussion: https://github.com/carbon-language/carbon-lang/pull/2460#discussion_r1046444433

Features:
* Move subtyping logic from Interpreter to TypeChecker, exposing subtyping as a series of access to `.base`.
    * Excludes function parameter conversion, which is still done in ::Convert due to parameters conversion being handled differently.

Changes:
* Add new `class BaseAccessExpression : public MemberAccessExpression`, allowing rewrites
* Handle `BaseAccessExpression` expression type in Interpreter
* Move subtyping logic to `TypeChecker::ImplicitlyConvert`
This commit is contained in:
Adrien Leravat
2022-12-21 19:01:02 -08:00
committed by GitHub
parent 6accdfff77
commit 026c4b9dc3
15 changed files with 226 additions and 5 deletions
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explorer/interpreter/interpreter.cpp
+32
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@@ -453,6 +453,18 @@ auto Interpreter::StepLvalue() -> ErrorOr<Success> {
return todo_.FinishAction(arena_->New<LValue>(field));
}
}
case ExpressionKind::BaseAccessExpression: {
const auto& access = cast<BaseAccessExpression>(exp);
if (act.pos() == 0) {
// Get LValue for expression.
return todo_.Spawn(std::make_unique<LValAction>(&access.object()));
} else {
// Append `.base` element to the address, and return the new LValue.
Address object = cast<LValue>(*act.results()[0]).address();
Address base = object.ElementAddress(&access.element());
return todo_.FinishAction(arena_->New<LValue>(base));
}
}
case ExpressionKind::IndexExpression: {
if (act.pos() == 0) {
// { {e[i] :: C, E, F} :: S, H}
@@ -884,6 +896,8 @@ auto Interpreter::Convert(Nonnull<const Value*> value,
CARBON_CHECK(pointee->kind() == Value::Kind::NominalClassValue)
<< "Unexpected pointer type";
// Conversion logic for subtyping for function arguments only.
// TODO: Drop when able to rewrite subtyping in TypeChecker for arguments.
const auto* dest_ptr = cast<PointerType>(destination_type);
std::optional<Nonnull<const NominalClassValue*>> class_subobj =
cast<NominalClassValue>(pointee);
@@ -1268,6 +1282,21 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
}
}
}
case ExpressionKind::BaseAccessExpression: {
const auto& access = cast<BaseAccessExpression>(exp);
if (act.pos() == 0) {
return todo_.Spawn(
std::make_unique<ExpressionAction>(&access.object()));
} else {
ElementPath::Component base_elt(&access.element(), std::nullopt,
std::nullopt);
const Value* value = act.results()[0];
CARBON_ASSIGN_OR_RETURN(Nonnull<const Value*> base_value,
value->GetElement(arena_, ElementPath(base_elt),
exp.source_loc(), value));
return todo_.FinishAction(base_value);
}
}
case ExpressionKind::IdentifierExpression: {
CARBON_CHECK(act.pos() == 0);
const auto& ident = cast<IdentifierExpression>(exp);
@@ -1578,6 +1607,9 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
}
case ExpressionKind::BuiltinConvertExpression: {
const auto& convert_expr = cast<BuiltinConvertExpression>(exp);
if (auto rewrite = convert_expr.rewritten_form()) {
return todo_.ReplaceWith(std::make_unique<ExpressionAction>(*rewrite));
}
if (act.pos() == 0) {
return todo_.Spawn(std::make_unique<ExpressionAction>(
convert_expr.source_expression()));