davrec added a comment. Great examples.
> Check this example out: https://godbolt.org/z/rsGsM6GrM > > template <class ...Ts> struct A { > template <class ...Us> struct B { > using type1 = void ((void (*...fps)(Ts, Us))); > }; > }; > using type2 = A<int, char>::B<short, bool>::type1; > > TypeAliasDecl 0x55ffe8b45368 <line:8:1, col:45> col:7 type2 'A<int, > char>::B<short, bool>::type1':'void ((void (*)(int, short), void (*)(char, > bool)))' > `-ElaboratedType 0x55ffe8b452f0 'A<int, char>::B<short, bool>::type1' > sugar > `-TypedefType 0x55ffe8b452d0 'A<int, char>::B<short, bool>::type1' sugar > |-TypeAlias 0x55ffe8b45258 'type1' > `-FunctionProtoType 0x55ffe8b451e0 'void ((void (*)(int, short), void > (*)(char, bool)))' cdecl > |-ParenType 0x55ffe8b12150 'void' sugar > | `-BuiltinType 0x55ffe8ac6370 'void' > |-PointerType 0x55ffe8b44550 'void (*)(int, short)' > | `-ParenType 0x55ffe8b444f0 'void (int, short)' sugar > | `-FunctionProtoType 0x55ffe8b444b0 'void (int, short)' cdecl > | |-BuiltinType 0x55ffe8ac6370 'void' > | |-SubstTemplateTypeParmType 0x55ffe8b44310 'int' sugar > | | |-TemplateTypeParmType 0x55ffe8b11440 'Ts' dependent > contains_unexpanded_pack depth 0 index 0 pack > | | | `-TemplateTypeParm 0x55ffe8b113c0 'Ts' > | | `-BuiltinType 0x55ffe8ac6410 'int' > | `-SubstTemplateTypeParmType 0x55ffe8b443c0 'short' sugar > | |-TemplateTypeParmType 0x55ffe8b11960 'Us' dependent > contains_unexpanded_pack depth 1 index 0 pack > | | `-TemplateTypeParm 0x55ffe8b118d8 'Us' > | `-BuiltinType 0x55ffe8ac63f0 'short' > `-PointerType 0x55ffe8b450c0 'void (*)(char, bool)' > `-ParenType 0x55ffe8b45060 'void (char, bool)' sugar > `-FunctionProtoType 0x55ffe8b447d0 'void (char, bool)' cdecl > |-BuiltinType 0x55ffe8ac6370 'void' > |-SubstTemplateTypeParmType 0x55ffe8b44630 'char' sugar > | |-TemplateTypeParmType 0x55ffe8b11440 'Ts' dependent > contains_unexpanded_pack depth 0 index 0 pack > | | `-TemplateTypeParm 0x55ffe8b113c0 'Ts' > | `-BuiltinType 0x55ffe8ac63b0 'char' > `-SubstTemplateTypeParmType 0x55ffe8b446e0 'bool' sugar > |-TemplateTypeParmType 0x55ffe8b11960 'Us' dependent > contains_unexpanded_pack depth 1 index 0 pack > | `-TemplateTypeParm 0x55ffe8b118d8 'Us' > `-BuiltinType 0x55ffe8ac6390 'bool' If it were as simple as the above case the Resugarer TreeTransform could say keep a map of `TemplateTypeParmType`s to current pack indices, and iterate those during each each `TransformSubstTemplateTypeParmType` call, but... > And in fact, a given parameter pack might be referenced more than one time in > a given pack expansion pattern: > > template <class ...Ts> struct A { > template <class ...Us> struct B { > using type1 = void ((void (*...fps)(Ts, Ts, Us))); > }; > }; > > Ie those two Ts are referencing the same argument within the pack, we can't > confuse that with an expansion. > > So think also about a case like the above, but where you are performing the > expansion just one time. It doesn't look like to me you can figure that out > from what Clang leaves behind in the AST at the moment. ...the different `Ts` are the same `TemplateTypeParmType`, so that wouldn't work. You're right, more info is needed. > We may need to create a new AST node, which is like a Subst variant of a > PackExpansionType, at the expansion loci. Or, maybe `TemplateTypeParmType` could store a number that would make it unique for each *instance* of it in a given expansion? Or just `SubstTemplateTypeParmType` could store this number in addition to its `TemplateTypeParmType`? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D128113/new/ https://reviews.llvm.org/D128113 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
