Fix grammar in diagnostic for wrong arity in a structured binding.

Author: zygoloid

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -470,8 +470,9 @@ def err_decomp_decl_not_alone : Error<
 def err_decomp_decl_requires_init : Error<
   "decomposition declaration %0 requires an initializer">;
 def err_decomp_decl_wrong_number_bindings : Error<
-  "type %0 decomposes into %2 elements, but %select{only |}3%1 "
-  "names were provided">;
+  "type %0 decomposes into %3 %plural{1:element|:elements}2, but "
+  "%select{%plural{0:no|:only %1}1|%1}4 "
+  "%plural{1:name was|:names were}1 provided">;
 def err_decomp_decl_unbindable_type : Error<
   "cannot decompose %select{union|non-class, non-array}1 type %2">;
 def err_decomp_decl_multiple_bases_with_members : Error<

clang/lib/Sema/SemaDeclCXX.cpp

@@ -902,7 +902,8 @@ static bool checkSimpleDecomposition(
     llvm::function_ref<ExprResult(SourceLocation, Expr *, unsigned)> GetInit) {
   if ((int64_t)Bindings.size() != NumElems) {
     S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
-        << DecompType << (unsigned)Bindings.size() << NumElems.toString(10)
+        << DecompType << (unsigned)Bindings.size()
+        << (unsigned)NumElems.getLimitedValue(UINT_MAX) << NumElems.toString(10)
         << (NumElems < Bindings.size());
     return true;
   }
@@ -1148,8 +1149,9 @@ static bool checkTupleLikeDecomposition(Sema &S,
                                         const llvm::APSInt &TupleSize) {
   if ((int64_t)Bindings.size() != TupleSize) {
     S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
-        << DecompType << (unsigned)Bindings.size() << TupleSize.toString(10)
-        << (TupleSize < Bindings.size());
+        << DecompType << (unsigned)Bindings.size()
+        << (unsigned)TupleSize.getLimitedValue(UINT_MAX)
+        << TupleSize.toString(10) << (TupleSize < Bindings.size());
     return true;
   }
 
@@ -1373,7 +1375,7 @@ static bool checkMemberDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
                       [](FieldDecl *FD) { return !FD->isUnnamedBitfield(); });
     assert(Bindings.size() != NumFields);
     S.Diag(Src->getLocation(), diag::err_decomp_decl_wrong_number_bindings)
-        << DecompType << (unsigned)Bindings.size() << NumFields
+        << DecompType << (unsigned)Bindings.size() << NumFields << NumFields
         << (NumFields < Bindings.size());
     return true;
   };

clang/test/SemaCXX/cxx1z-decomposition.cpp

@@ -4,6 +4,21 @@ void use_from_own_init() {
   auto [a] = a; // expected-error {{binding 'a' cannot appear in the initializer of its own decomposition declaration}}
 }
 
+void num_elems() {
+  struct A0 {} a0;
+  int a1[1], a2[2];
+
+  auto [] = a0; // expected-warning {{does not allow a decomposition group to be empty}}
+  auto [v1] = a0; // expected-error {{type 'A0' decomposes into 0 elements, but 1 name was provided}}
+  auto [] = a1; // expected-error {{type 'int [1]' decomposes into 1 element, but no names were provided}} expected-warning {{empty}}
+  auto [v2] = a1;
+  auto [v3, v4] = a1; // expected-error {{type 'int [1]' decomposes into 1 element, but 2 names were provided}}
+  auto [] = a2; // expected-error {{type 'int [2]' decomposes into 2 elements, but no names were provided}} expected-warning {{empty}}
+  auto [v5] = a2; // expected-error {{type 'int [2]' decomposes into 2 elements, but only 1 name was provided}}
+  auto [v6, v7] = a2;
+  auto [v8, v9, v10] = a2; // expected-error {{type 'int [2]' decomposes into 2 elements, but 3 names were provided}}
+}
+
 // As a Clang extension, _Complex can be decomposed.
 float decompose_complex(_Complex float cf) {
   static _Complex float scf;