[AST] Add swift::getParameterList

Author: hamishknight

include/swift/AST/Decl.h

@@ -7286,6 +7286,9 @@ inline EnumElementDecl *EnumDecl::getUniqueElement(bool hasValue) const {
   return result;
 }
 
+/// Retrieve the parameter list for a given declaration.
+ParameterList *getParameterList(ValueDecl *source);
+
 /// Retrieve parameter declaration from the given source at given index.
 const ParamDecl *getParameterAt(const ValueDecl *source, unsigned index);
 

lib/AST/Decl.cpp

@@ -6465,17 +6465,19 @@ DeclName AbstractFunctionDecl::getEffectiveFullName() const {
   return DeclName();
 }
 
-const ParamDecl *swift::getParameterAt(const ValueDecl *source, unsigned index) {
-  const ParameterList *paramList;
+ParameterList *swift::getParameterList(ValueDecl *source) {
   if (auto *AFD = dyn_cast<AbstractFunctionDecl>(source)) {
-    paramList = AFD->getParameters();
+    return AFD->getParameters();
   } else if (auto *EED = dyn_cast<EnumElementDecl>(source)) {
-    paramList = EED->getParameterList();
+    return EED->getParameterList();
   } else {
-    paramList = cast<SubscriptDecl>(source)->getIndices();
+    return cast<SubscriptDecl>(source)->getIndices();
   }
+}
 
-  return paramList->get(index);
+const ParamDecl *swift::getParameterAt(const ValueDecl *source,
+                                       unsigned index) {
+  return getParameterList(const_cast<ValueDecl *>(source))->get(index);
 }
 
 Type AbstractFunctionDecl::getMethodInterfaceType() const {

lib/Sema/TypeCheckProtocol.cpp

@@ -253,14 +253,6 @@ static bool checkObjCWitnessSelector(ValueDecl *req, ValueDecl *witness) {
   return false;
 }
 
-static ParameterList *getParameterList(ValueDecl *value) {
-  if (auto func = dyn_cast<AbstractFunctionDecl>(value))
-    return func->getParameters();
-
-  auto subscript = cast<SubscriptDecl>(value);
-  return subscript->getIndices();
-}
-
 // Find a standin declaration to place the diagnostic at for the
 // given accessor kind.
 static ValueDecl *getStandinForAccessor(AbstractStorageDecl *witness,