================
@@ -639,7 +639,14 @@
ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
llvm::to_vector_of<TemplateArgument>(MLTAL.getOutermost());
unsigned Offset = 0;
for (unsigned I = 0, MappedIndex = 0; I < Used.size(); I++) {
- TemplateArgument Arg;
+ // For template parameters that are not used during substitution, they
+ // still need to exist in the MLTAL since template parameter indices remain
+ // unchanged.
+ // We need a placeholder to represent them: a null TemplateArgument doesn't
+ // fit well due to non-null assumptions elsewhere. An empty pack serves
this
+ // purpose, and substitution checks would catch any mistakes if we really
+ // messed anything up.
+ TemplateArgument Arg = TemplateArgument::getEmptyPack();
----------------
cor3ntin wrote:
Aren't we gonna run into the same issue of having empty packs where we don't
expect them, instead of null arguments where we don't expect them - do we need
a new kind of dummy template argument?
https://github.com/llvm/llvm-project/pull/174698
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