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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/generic.cpp
+1 -1
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@@ -344,7 +344,7 @@ static auto MakeGenericEvalBlock(Context& context, SemIR::GenericId generic_id,
context, generic_id, region, context.insts().GetLocId(inst_id),
constants_in_generic, inside_redeclaration, inst.type_id());
// If the generic declaration is invalid, it can result in an error.
if (type_id == SemIR::ErrorInst::SingletonTypeId) {
if (type_id == SemIR::ErrorInst::TypeId) {
break;
}
// TODO: Eventually, completeness requirements should be modeled as