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Allow incomplete return types in function declarations. (#3875)

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Move completeness check to the point where the function is defined or
first called. This means we also defer deciding whether the function has
a return slot until that point. Instead of storing a return slot per
function, store the location of the return storage, which may or may not
be used, and compute and store a separate flag saying whether to use it
at the point of first use or definition.

This is the final piece in supporting simple `Make` functions in classes
as a replacement for constructors.
This commit is contained in:
Richard Smith
2024-04-11 07:23:56 +00:00
committed by GitHub
parent 28ceb4dd4e
commit 1b335402d1
173 changed files with 980 additions and 615 deletions
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toolchain/check/return.cpp
+10 -8
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@@ -39,9 +39,8 @@ static auto NoteReturnType(Context::DiagnosticBuilder& diag,
const SemIR::Function& function) {
CARBON_DIAGNOSTIC(ReturnTypeHereNote, Note,
"Return type of function is `{0}`.", SemIR::TypeId);
// TODO: This is using the location of the `fn` keyword. Find the location of
// the return type.
diag.Note(function.decl_id, ReturnTypeHereNote, function.return_type_id);
diag.Note(function.return_storage_id, ReturnTypeHereNote,
function.return_type_id);
}
// Produces a note pointing at the currently in scope `returned var`.
@@ -82,8 +81,8 @@ auto CheckReturnedVar(Context& context, Parse::NodeId returned_node,
// The variable aliases the return slot if there is one. If not, it has its
// own storage.
if (function.return_slot_id.is_valid()) {
return function.return_slot_id;
if (function.has_return_slot()) {
return function.return_storage_id;
}
return context.AddInst({name_node, SemIR::VarStorage{type_id, name_id}});
}
@@ -136,8 +135,11 @@ auto BuildReturnWithExpr(Context& context, Parse::ReturnStatementId node_id,
NoteReturnedVar(diag, returned_var_id);
diag.Emit();
expr_id = SemIR::InstId::BuiltinError;
} else if (function.return_slot_id.is_valid()) {
expr_id = Initialize(context, node_id, function.return_slot_id, expr_id);
} else if (function.has_return_slot()) {
expr_id = Initialize(context, node_id, function.return_storage_id, expr_id);
} else if (function.return_slot == SemIR::Function::ReturnSlot::Error) {
// Don't produce a second error complaining the return type is incomplete.
expr_id = SemIR::InstId::BuiltinError;
} else {
expr_id = ConvertToValueOfType(context, node_id, expr_id,
function.return_type_id);
@@ -158,7 +160,7 @@ auto BuildReturnVar(Context& context, Parse::ReturnStatementId node_id)
returned_var_id = SemIR::InstId::BuiltinError;
}
if (!function.return_slot_id.is_valid()) {
if (!function.has_return_slot()) {
// If we don't have a return slot, we're returning by value. Convert to a
// value expression.
returned_var_id = ConvertToValueExpr(context, returned_var_id);