[NFC] AST: Define SubstitutionMap::getInnermostReplacementTypes

include/swift/AST/SubstitutionMap.h

@@ -150,6 +150,10 @@ class SubstitutionMap {
   /// generic parameters.
   ArrayRef<Type> getReplacementTypes() const;
 
+  /// Retrieve the array of replacement types for the innermost generic
+  /// parameters.
+  ArrayRef<Type> getInnermostReplacementTypes() const;
+
   /// Query whether any replacement types in the map contain archetypes.
   bool hasArchetypes() const;
 

include/swift/AST/Types.h

@@ -1803,13 +1803,10 @@ class TypeAliasType final
     return *getTrailingObjects<SubstitutionMap>();
   }
 
-  /// Get the innermost generic arguments, which correspond to the generic
-  /// arguments that are directly applied to the typealias declaration in
-  /// produced by \c getDecl().
-  ///
-  /// The result can be empty, if the declaration itself is non-generic but
-  /// the parent is generic.
-  SmallVector<Type, 2> getInnermostGenericArgs() const;
+  /// Get the direct generic arguments, which correspond to the generic
+  /// arguments that are directly applied to the typealias declaration
+  /// this type references.
+  ArrayRef<Type> getDirectGenericArgs() const;
 
   // Support for FoldingSet.
   void Profile(llvm::FoldingSetNodeID &id) const;

lib/AST/ASTDumper.cpp

@@ -3506,7 +3506,7 @@ namespace {
       if (T->getParent())
         printRec("parent", T->getParent());
 
-      for (auto arg : T->getInnermostGenericArgs())
+      for (const auto arg : T->getDirectGenericArgs())
         printRec(arg);
       PrintWithColorRAII(OS, ParenthesisColor) << ')';
     }

lib/AST/ASTPrinter.cpp

@@ -3727,7 +3727,7 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
     }
 
     printQualifiedType(T);
-    printGenericArgs(T->getInnermostGenericArgs());
+    printGenericArgs(T->getDirectGenericArgs());
   }
 
   void visitParenType(ParenType *T) {

lib/AST/SubstitutionMap.cpp

@@ -97,6 +97,13 @@ ArrayRef<Type> SubstitutionMap::getReplacementTypes() const {
   return getReplacementTypesBuffer();
 }
 
+ArrayRef<Type> SubstitutionMap::getInnermostReplacementTypes() const {
+  if (empty()) return { };
+
+  return getReplacementTypes().take_back(
+      getGenericSignature()->getInnermostGenericParams().size());
+}
+
 GenericSignature SubstitutionMap::getGenericSignature() const {
   return storage ? storage->getGenericSignature() : nullptr;
 }

lib/AST/Type.cpp

@@ -1385,26 +1385,12 @@ Type SugarType::getSinglyDesugaredTypeSlow() {
   return UnderlyingType;
 }
 
-SmallVector<Type, 2> TypeAliasType::getInnermostGenericArgs() const {
-  SmallVector<Type, 2> result;
+ArrayRef<Type> TypeAliasType::getDirectGenericArgs() const {
+  if (!typealias->isGeneric()) return { };
 
-  // If the typealias is not generic, there are no generic arguments
-  if (!typealias->isGeneric()) return result;
-
-  // If the substitution map is empty, bail out.
-  auto subMap = getSubstitutionMap();
-  if (subMap.empty()) return result;
-
-  // Retrieve the substitutions for the generic parameters (only).
-  auto genericSig = subMap.getGenericSignature();
-  unsigned numAllGenericParams = genericSig->getGenericParams().size();
-  unsigned numMyGenericParams = typealias->getGenericParams()->size();
-  result.reserve(numMyGenericParams);
-  unsigned startIndex = numAllGenericParams - numMyGenericParams;
-  for (auto gp : genericSig->getGenericParams().slice(startIndex)) {
-    result.push_back(Type(gp).subst(subMap));
-  }
-  return result;
+  // Otherwise, the innermost replacement types are the direct
+  // generic arguments.
+  return getSubstitutionMap().getInnermostReplacementTypes();
 }
 
 unsigned GenericTypeParamType::getDepth() const {

lib/AST/TypeWalker.cpp

@@ -39,7 +39,7 @@ class Traversal : public TypeVisitor<Traversal, bool>
     if (auto parent = ty->getParent())
       if (doIt(parent)) return true;
 
-    for (auto arg : ty->getInnermostGenericArgs())
+    for (const auto arg : ty->getDirectGenericArgs())
       if (doIt(arg))
         return true;