davrec added inline comments.
================
Comment at: clang/lib/Sema/SemaTemplate.cpp:534-540
+ QualType TransformSubstTemplateTypeParmType(TypeLocBuilder &TLB,
+ SubstTemplateTypeParmTypeLoc TL)
{
+ QualType QT = TL.getType();
+ const SubstTemplateTypeParmType *T = TL.getTypePtr();
+ Decl *ReplacedDecl = T->getReplacedDecl();
+
+ Optional<unsigned> PackIndex = T->getPackIndex();
----------------
davrec wrote:
> Haven't thought this through fully, but: would the following make D128113
> (storing the pack index in the STTPT or introducing a new sugar type)
> unnecessary?
> ```
> map<pair<Decl *, unsigned>, Optional<unsigned>> CurPackIndices;
> QualType TransformSubstTemplateTypeParmType(TypeLocBuilder &TLB,
> SubstTemplateTypeParmTypeLoc
> TL) {
> QualType QT = TL.getType();
> const SubstTemplateTypeParmType *T = TL.getTypePtr();
> Decl *ReplacedDecl = T->getReplacedDecl();
>
> Optional<unsigned> &PackIndex = CurPackIndices[{ReplacedDecl,
> T->getIndex()}];
> if (!PackIndex && T->getReplacedParameter()->isParameterPack())
> PackIndex = 0;
>
> ...
>
> if (PackIndex)
> ++PackIndex;
> // ^ maybe reset to zero if > pack size, if we might be resugaring
> multiple expansions
> return QT;
> }
> ```
Disregard above - upon further thought this does not improve the things; there
still isn't enough info about the substitutions. I.e. the issue is with
substitutions, not the parameter declarations for which they are substituted.
So a sugar node wrapping the STTPTs to represent each expansion instance really
is needed. Then when we have that I think we could map from those to their
current pack indices per the above to infer the pack indices.
For this sugar node, maybe we could just modify `SubstTemplateTypeParmPackType`
so it is not just canonical, but can also be sugar wrapping substituted STTPTs,
as opposed to introducing a new Subst* type class?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D127695/new/
https://reviews.llvm.org/D127695
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