================
@@ -2583,11 +2580,27 @@ struct ConvertConstructorToDeductionGuideTransform {
// -- The types of the function parameters are those of the constructor.
for (auto *OldParam : TL.getParams()) {
- ParmVarDecl *NewParam =
- transformFunctionTypeParam(OldParam, Args, MaterializedTypedefs);
- if (NestedPattern && NewParam)
+ ParmVarDecl *NewParam = OldParam;
+ // Given
+ // template <class T> struct C {
+ // template <class U> struct D {
+ // template <class V> D(U, V);
+ // };
+ // };
+ // First, transform all the references to template parameters that are
+ // defined outside of the surrounding class template. That is T in the
+ // above example.
+ if (NestedPattern) {
NewParam = transformFunctionTypeParam(NewParam, OuterInstantiationArgs,
MaterializedTypedefs);
+ if (!NewParam)
+ return QualType();
+ }
+ // Then, transform all the references to template parameters that are
+ // defined at the class template and the constructor. In this example,
+ // they're U and V, respectively.
+ NewParam =
+ transformFunctionTypeParam(NewParam, Args, MaterializedTypedefs);
----------------
zyn0217 wrote:
I think that's just fine, although it looks weird: those lines are merely
"creating" new template parameters rather than doing type substitution. (it's
applying a `TemplateDeclInstantiator` with the instantiating arguments - the
only valuable part from these arguments is the depth we're supposed to deduct,
and the type isn't something we're concerned about at that time.)
Frankly, I have to say I didn't fully understand why we have such discrepancies
(use the `transformTemplateParameter` first and then a
`TemplateDeclInstantiator` for nested cases). I was expecting that perhaps we
could unify them in one call. I think it warrants a separate refactoring PR,
then.
https://github.com/llvm/llvm-project/pull/91628
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