zyn0217 wrote: Thanks for the prompt review.
> There is an ambiguous case that I'm a little concerned about: if the alias > template parameter and the underlying template parameter have the same name, > the synthesized deduction guide may end up with two template parameters with > the same name. For instance, see [this > example](https://godbolt.org/z/q1n7Edzcz). In such cases, we cannot > distinguish between the `T1` parameters from the function signature `auto > (T1, T1) -> X<T1, double>`. Yeah, this is indeed an interesting case. I played it a bit and realized we would now dump a confusing diagnostic for it: ```cpp template <class T, class U> struct X { X(T, U); }; template <class T, class T1> X(T, T1) -> X<T, double>; template <class T1> using AX = X<T1, double>; AX s(1); ``` would result in ``` note: candidate function template not viable: requires 2 arguments, but 1 was provided note: implicit deduction guide declared as 'template <class T1, class T1> requires __is_deducible(AX, X<type-parameter-0-0, double>) AX(type-parameter-0-0, type-parameter-0-1) -> X<type-parameter-0-0, double>' ``` The printed template parameter list is actually syntactically illegal simply because we merely dump the synthesized parameter list, which actually reuses the written parameter names. I think a solution would be, if we realize there's a name clash when building up a list, we make up and use a different parameter name. (This can be left as a follow-up because I feel we're less likely to run into this case.) Regarding the disambiguation, we could already do that through an AST dump. For the case above, I ran an AST dump locally and got the following: ``` |-FunctionTemplateDecl 0x7f90695f3970 <line:9:1, line:10:24> col:1 implicit <deduction guide for AX> | |-TemplateTypeParmDecl 0x7f90695f3068 <line:9:11, col:17> col:17 class depth 0 index 0 T1 | |-TypeTraitExpr 0x7f90695f3858 <line:10:1> 'bool' __is_deducible | | |-DeducedTemplateSpecializationType 0x7f90695f2e60 'AX' dependent | | | `-name: 'AX' | | | `-TypeAliasTemplateDecl 0x7f90695f1d70 <line:9:1, line:10:24> col:1 AX | | `-TemplateSpecializationType 0x7f90695f35a0 'X<T1, double>' dependent | | |-name: 'X' qualified | | | `-ClassTemplateDecl 0x7f90695ce158 <line:1:1, line:4:1> line:2:8 X | | |-TemplateArgument type 'T1':'type-parameter-0-0' | | | `-SubstTemplateTypeParmType 0x7f90695f32d0 'T1' sugar dependent class depth 0 index 0 T | | | |-FunctionTemplate 0x7f90695f18d0 '<deduction guide for X>' | | | `-TemplateTypeParmType 0x7f90695f30c0 'T1' dependent depth 0 index 0 | | | `-TemplateTypeParm 0x7f90695f3068 'T1' | | `-TemplateArgument type 'double' | | `-SubstTemplateTypeParmType 0x7f90695f3320 'double' sugar class depth 0 index 1 U | | |-FunctionTemplate 0x7f90695f18d0 '<deduction guide for X>' | | `-BuiltinType 0x7f906957d780 'double' | `-CXXDeductionGuideDecl 0x7f90695f38a8 <line:9:1, line:10:24> col:1 implicit <deduction guide for AX> 'auto (X<T1, double>) -> X<T1, double>' | `-ParmVarDecl 0x7f90695f3438 <line:2:8> col:8 'X<T1, double>' ``` Note that we can see the `T1`'s canonical type at the node of `TemplateArgument`. https://github.com/llvm/llvm-project/pull/99840 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
