[c++20] Disallow template argument deduction from a braced-init-list

containing designators. The C++20 wording doesn't actually say what
happens in this case, but treating this as a non-deduced context seems
like the most natural behavior.

(We might want to consider deducing through array designators as an
extension in the future, but will need to be careful to deduce the array
bound properly if we do so. That's not permitted herein.)

llvm-svn: 370555

2 files changed, 20 insertions, 2 deletions

diff --git a/clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp b/clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp
index 9a82ec4a7bd..b5d6bd68f1f 100644
--- a/clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp
+++ b/clang/test/SemaCXX/cxx0x-initializer-stdinitializerlist.cpp
@@ -29,9 +29,9 @@ namespace std {
     typedef const _E* iterator;
     typedef const _E* const_iterator;
 
-    initializer_list() : __begin_(nullptr), __size_(0) {}
+    constexpr initializer_list() : __begin_(nullptr), __size_(0) {}
 
-    size_t    size()  const {return __size_;}
+    constexpr size_t    size()  const {return __size_;}
     const _E* begin() const {return __begin_;}
     const _E* end()   const {return __begin_ + __size_;}
   };
@@ -354,3 +354,14 @@ namespace no_conversion_after_auto_list_deduction {
   struct Y { using T = std::initializer_list<Y>(*)(); operator T(); };
   auto (*y)() = { Y() }; // expected-error {{from initializer list}}
 }
+
+namespace designated_init {
+  constexpr auto a = {.a = 1, .b = 2}; // expected-error {{cannot deduce}}
+  constexpr auto b = {[0] = 1, [4] = 2}; // expected-error {{cannot deduce}} expected-warning {{C99}}
+  constexpr auto c = {1, [4] = 2}; // expected-error {{cannot deduce}} expected-warning 2{{C99}} expected-note {{here}}
+  constexpr auto d = {1, [0] = 2}; // expected-error {{cannot deduce}} expected-warning 2{{C99}} expected-note {{here}}
+
+  // If we ever start accepting the above, these assertions should pass.
+  static_assert(c.size() == 5, "");
+  static_assert(d.size() == 1, "");
+}
diff --git a/clang/test/SemaTemplate/deduction.cpp b/clang/test/SemaTemplate/deduction.cpp
index be86f18729d..64fef8e5f52 100644
--- a/clang/test/SemaTemplate/deduction.cpp
+++ b/clang/test/SemaTemplate/deduction.cpp
@@ -539,3 +539,10 @@ namespace dependent_list_deduction {
 #endif
   }
 }
+
+namespace designators {
+  template<typename T, int N> constexpr int f(T (&&)[N]) { return N; } // expected-note 2{{couldn't infer template argument 'T'}}
+  static_assert(f({1, 2, [20] = 3}) == 3, ""); // expected-error {{no matching function}} expected-warning 2{{C99}} expected-note {{}}
+
+  static_assert(f({.a = 1, .b = 2}) == 3, ""); // expected-error {{no matching function}}
+}