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Fix type alias declaration evaluation problem (#854 #1439)

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This commit is contained in:
gingerBill
2022-02-03 13:34:31 +00:00
parent df8bdac33f
commit 35c90fe124
3 changed files with 137 additions and 18 deletions
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39
src/check_decl.cpp
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@@ -385,7 +385,44 @@ void check_const_decl(CheckerContext *ctx, Entity *e, Ast *type_expr, Ast *init,
Operand operand = {};
if (init != nullptr) {
Entity *entity = nullptr;
Entity *entity = check_entity_from_ident_or_selector(ctx, init);
if (entity != nullptr && entity->kind == Entity_TypeName) {
// NOTE(bill, 2022-02-03): This is used to solve the problem caused by type aliases
// being "confused" as constants
//
// A :: B
// C :: proc "c" (^A)
// B :: struct {x: C}
//
// A gets evaluated first, and then checks B.
// B then checks C.
// C then tries to check A which is unresolved but thought to be a constant.
// Therefore within C's check, A errs as "not a type".
//
// This is because a const declaration may or may not be a type and this cannot
// be determined from a syntactical standpoint.
// This check allows the compiler to override the entity to be checked as a type.
//
// There is no problem if B is prefixed with the `#type` helper enforcing at
// both a syntax and semantic level that B must be a type.
//
// A :: #type B
//
// This approach is not fool proof and can fail in case such as:
//
// X :: type_of(x)
// X :: Foo(int).Type
//
// Since even these kind of declarations may cause weird checking cycles.
// For the time being, these are going to be treated as an unfortunate error
// until there is a proper delaying system to try declaration again if they
// have failed.
e->kind = Entity_TypeName;
check_type_decl(ctx, e, init, named_type);
return;
}
entity = nullptr;
if (init->kind == Ast_Ident) {
entity = check_ident(ctx, &operand, init, nullptr, e->type, true);
} else if (init->kind == Ast_SelectorExpr) {