Fix template argument deduction when only some of a parameter pack is a non-deduced context.

When a parameter pack has multiple corresponding arguments, and some subset of
them are overloaded functions, it's possible that some subset of the parameters
are non-deduced contexts. In such a case, keep deducing from the remainder of
the arguments, and resolve the incomplete pack against whatever other
deductions we've performed for the pack.

GCC, MSVC, and ICC give three different bad behaviors for this case; what we do
now (and what we did before) don't exactly match any of them, sadly :( I'm
getting a core issue opened to specify more precisely how this should be
handled.

llvm-svn: 290923

1 files changed, 38 insertions, 0 deletions

diff --git a/clang/test/SemaTemplate/deduction.cpp b/clang/test/SemaTemplate/deduction.cpp
index 69a3817f735..fdf21bc79a5 100644
--- a/clang/test/SemaTemplate/deduction.cpp
+++ b/clang/test/SemaTemplate/deduction.cpp
@@ -362,3 +362,41 @@ namespace deduction_after_explicit_pack {
     g<int, float&, double&>(a, b, c, &c); // ok
   }
 }
+
+namespace overload_vs_pack {
+  void f(int);
+  void f(float);
+  void g(double);
+
+  template<typename ...T> struct X {};
+  template<typename ...T> void x(T...);
+
+  template<typename ...T> struct Y { typedef int type(typename T::error...); };
+  template<> struct Y<int, float, double> { typedef int type; };
+
+  template<typename ...T> typename Y<T...>::type g1(X<T...>, void (*...fns)(T)); // expected-note {{deduced conflicting types for parameter 'T' (<int, float> vs. <(no value), double>)}}
+  template<typename ...T> typename Y<T...>::type g2(void(*)(T...), void (*...fns)(T)); // expected-note {{deduced conflicting types for parameter 'T' (<int, float> vs. <(no value), double>)}}
+
+  template<typename T> int &h1(decltype(g1(X<int, float, T>(), f, f, g)) *p);
+  template<typename T> float &h1(...);
+
+  template<typename T> int &h2(decltype(g2(x<int, float, T>, f, f, g)) *p);
+  template<typename T> float &h2(...);
+
+  int n1 = g1(X<int, float>(), f, g); // expected-error {{no matching function}}
+  int n2 = g2(x<int, float>, f, g); // expected-error {{no matching function}}
+  int n3 = g1(X<int, float, double, char>(), f);
+  int n4 = g2(x<int, float, double, long>, f);
+
+  int &a1 = h1<double>(0); // ok, skip deduction for 'f's, deduce matching value from 'g'
+  int &a2 = h2<double>(0);
+
+  float &b1 = h1<float>(0); // deduce mismatching value from 'g', so we do not trigger instantiation of Y
+  float &b2 = h2<float>(0);
+
+  template<typename ...T> int partial_deduction(void (*...f)(T)); // expected-note {{deduced incomplete pack <(no value), double> for template parameter 'T'}}
+  int pd1 = partial_deduction(f, g); // expected-error {{no matching function}}
+
+  template<typename ...T> int partial_deduction_2(void (*...f)(T), ...); // expected-note {{deduced incomplete pack <(no value), double> for template parameter 'T'}}
+  int pd2 = partial_deduction_2(f, g); // expected-error {{no matching function}}
+}