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Drop Singleton from ErrorInst::SingletonInstId and similar (#5304)

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We frequently want to operate on singletons. Per discussion, drop
`Singleton` to make the code shorter.

This started off as wanting to write `inst_id.is_error()`, but the
dependency relationship between ids.h and singleton_insts.h would
require some kind of delayed evaluation to allow the implementation to
remain in headers (which I suspect is helpful to have for inlining). I
could have added something like `IsErrorInst`, forward declared in ids.h
and defined in singleton_insts.h (which would always be included by
typed_insts.h), but the template approach felt like a decent balance
between (a) removing the boilerplate `::SingletonInstId`, (b)
understandability, (c) still visually mirroring if we immediately return
a singleton, and (d) flexibility for more than just `ErrorInst`. But TBH
I'd probably still have written `is_error()` if it didn't require
addressing the cross-header cycle.

Then I tried `SemIR::InstId::Is<SemIR::ErrorInst>`, which generally
worked with types but generated the complaint that it didn't shorten
*all* singleton uses. So pulling back on `::Is`, and instead just
dropping `Singleton`.
This commit is contained in:
Jon Ross-Perkins
2025-04-15 22:40:29 +00:00
committed by GitHub
parent 838417e358
commit 4923445e3a
64 changed files with 489 additions and 539 deletions
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toolchain/check/return.cpp
+4 -4
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@@ -145,7 +145,7 @@ auto BuildReturnWithExpr(Context& context, Parse::ReturnStatementId node_id,
auto diag = context.emitter().Build(node_id, ReturnStatementDisallowExpr);
NoteNoReturnTypeProvided(diag, function);
diag.Emit();
expr_id = SemIR::ErrorInst::SingletonInstId;
expr_id = SemIR::ErrorInst::InstId;
} else if (returned_var_id.has_value()) {
CARBON_DIAGNOSTIC(
ReturnExprWithReturnedVar, Error,
@@ -153,11 +153,11 @@ auto BuildReturnWithExpr(Context& context, Parse::ReturnStatementId node_id,
auto diag = context.emitter().Build(node_id, ReturnExprWithReturnedVar);
NoteReturnedVar(diag, returned_var_id);
diag.Emit();
expr_id = SemIR::ErrorInst::SingletonInstId;
expr_id = SemIR::ErrorInst::InstId;
} else if (!return_info.is_valid()) {
// We already diagnosed that the return type is invalid. Don't try to
// convert to it.
expr_id = SemIR::ErrorInst::SingletonInstId;
expr_id = SemIR::ErrorInst::InstId;
} else if (return_info.has_return_slot()) {
return_slot_id = GetCurrentReturnSlot(context);
CARBON_CHECK(return_slot_id.has_value());
@@ -181,7 +181,7 @@ auto BuildReturnVar(Context& context, Parse::ReturnStatementId node_id)
CARBON_DIAGNOSTIC(ReturnVarWithNoReturnedVar, Error,
"`return var;` with no `returned var` in scope");
context.emitter().Emit(node_id, ReturnVarWithNoReturnedVar);
returned_var_id = SemIR::ErrorInst::SingletonInstId;
returned_var_id = SemIR::ErrorInst::InstId;
}
auto return_slot_id = GetCurrentReturnSlot(context);