Sema: Remove TupleType::getVarArgsBaseType()

Or, actually, now that there's only one usage left move it to CSDiag.
Hopefully, both vararg tuple types and CSDiag are going away
eventually.

Author: slavapestov

include/swift/AST/Types.h

@@ -1876,11 +1876,6 @@ class TupleType final : public TypeBase, public llvm::FoldingSetNode,
   /// return the element index, otherwise return -1.
   int getNamedElementId(Identifier I) const;
 
-  /// If this tuple has a varargs element to it, return the base type of the
-  /// varargs element (i.e., if it is "Int...", this returns Int, not [Int]).
-  /// Otherwise, this returns Type().
-  Type getVarArgsBaseType() const;
-  
   /// Returns true if this tuple has inout elements.
   bool hasInOutElement() const {
     return static_cast<bool>(Bits.TupleType.HasInOutElement);

lib/AST/Type.cpp

@@ -2422,18 +2422,6 @@ int TupleType::getNamedElementId(Identifier I) const {
   return -1;
 }
 
-/// If this tuple has a varargs element to it, return the base type of the
-/// varargs element (i.e., if it is "Int...", this returns Int, not [Int]).
-/// Otherwise, this returns Type().
-Type TupleType::getVarArgsBaseType() const {
-  for (unsigned i = 0, e = Bits.TupleType.Count; i != e; ++i) {
-    if (getTrailingObjects<TupleTypeElt>()[i].isVararg())
-      return getTrailingObjects<TupleTypeElt>()[i].getVarargBaseTy();
-  }
-  
-  return Type();
-}
-
 
 ArchetypeType::ArchetypeType(
   const ASTContext &Ctx,

lib/Sema/CSDiag.cpp

@@ -8296,7 +8296,16 @@ bool FailureDiagnosis::visitTupleExpr(TupleExpr *TE) {
   }
 
   if (!variadicArgs.empty()) {
-    auto varargsTy = contextualTT->getVarArgsBaseType();
+    Type varargsTy;
+    for (auto &elt : contextualTT->getElements()) {
+      if (elt.isVararg()) {
+        varargsTy = elt.getVarargBaseTy();
+        break;
+      }
+    }
+
+    assert(varargsTy);
+
     for (unsigned i = 0, e = variadicArgs.size(); i != e; ++i) {
       unsigned inArgNo = variadicArgs[i];