Cache generic signature instantiations

Author: ahejlsberg

src/compiler/checker.ts

@@ -4232,7 +4232,7 @@ namespace ts {
  for (const baseSig of baseSignatures) {
  const typeParamCount = baseSig.typeParameters ? baseSig.typeParameters.length : 0;
  if (typeParamCount === typeArgCount) {
- const sig = typeParamCount ? getSignatureInstantiation(baseSig, typeArguments) : cloneSignature(baseSig);
+ const sig = typeParamCount ? createSignatureInstantiation(baseSig, typeArguments) : cloneSignature(baseSig);
  sig.typeParameters = classType.localTypeParameters;
  sig.resolvedReturnType = classType;
  result.push(sig);
@@ -4982,6 +4982,12 @@ namespace ts {
  }
 
  function getSignatureInstantiation(signature: Signature, typeArguments: Type[]): Signature {
+ const instantiations = signature.instantiations || (signature.instantiations = createMap<Signature>());
+ const id = getTypeListId(typeArguments);
+ return instantiations[id] || (instantiations[id] = createSignatureInstantiation(signature, typeArguments));
+ }
+
+ function createSignatureInstantiation(signature: Signature, typeArguments: Type[]): Signature {
  return instantiateSignature(signature, createTypeMapper(signature.typeParameters, typeArguments), /*eraseTypeParameters*/ true);
  }
 

src/compiler/types.ts

@@ -2923,6 +2923,8 @@ namespace ts {
  isolatedSignatureType?: ObjectType; // A manufactured type that just contains the signature for purposes of signature comparison
  /* @internal */
  typePredicate?: TypePredicate;
+ /* @internal */
+ instantiations?: Map<Signature>; // Generic signature instantiation cache
  }
 
  export const enum IndexKind {