Commit bfd64335 authored by Richard Smith's avatar Richard Smith
Browse files

Fix merging of two arity-only pack deductions. 

If we deduced the arity of a pack in two different ways, but didn't
deduce an element of the pack in either of those deductions, we'd merge
that element to produce a null template argument, which we'd incorrectly
interpret as the merge having failed.

Testcase based on one supplied by Hubert Tong.
parent a19461d9

clang/lib/Sema/SemaTemplateDeduction.cpp

+1 −1
Original line number Diff line number Diff line
@@ -355,7 +355,7 @@ checkDeducedTemplateArguments(ASTContext &Context, 
      TemplateArgument Merged = checkDeducedTemplateArguments(

          Context, DeducedTemplateArgument(*XA, X.wasDeducedFromArrayBound()),

          DeducedTemplateArgument(*YA, Y.wasDeducedFromArrayBound()));

      if (Merged.isNull())

      if (Merged.isNull() && !(XA->isNull() && YA->isNull()))

        return DeducedTemplateArgument();

      NewPack.push_back(Merged);

    }

clang/test/SemaTemplate/deduction.cpp

+16 −0
Original line number Diff line number Diff line
@@ -581,3 +581,19 @@ namespace PR44890 { 
    return w.get<0>();

  }

}



namespace merge_size_only_deductions {

#if __cplusplus >= 201703L

  // Based on a testcase by Hubert Tong.

  template<typename ...> struct X {};

  template<auto ...> struct Y {};

  template<typename T> struct id { using Type = T; };



  template<typename ...T, typename T::Type ...V>

    int f(X<char [V] ...>, Y<V ...>, X<T ...>);



  using size_t = __SIZE_TYPE__;

  int a = f(X<char [1], char [2]>(), Y<(size_t)1, (size_t)2>(), X<id<size_t>, id<size_t>>());

  int b = f(X<char [1], char [2]>(), Y<1, 2>(), X<id<int>, id<int>>());

#endif

}