From f8fd1fd29f7975fcc3aeac8675c2cb107da33065 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 12 Dec 2022 15:58:39 -0800
Subject: [PATCH] Cache isConstTypeVariable check

---
 src/compiler/checker.ts | 17 +++++++++++------
 src/compiler/types.ts   | 12 +++++++-----
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 12f4b92ed34..b947e842e31 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13212,11 +13212,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return hasNonCircularBaseConstraint(typeParameter) ? getConstraintFromTypeParameter(typeParameter) : undefined;
     }
 
-    function isConstTypeVariable(type: Type): boolean {
-        return !!(type.flags & TypeFlags.TypeParameter && some((type as TypeParameter).symbol?.declarations, d => hasSyntacticModifier(d, ModifierFlags.Const)) ||
-            type.flags & TypeFlags.IndexedAccess && isConstTypeVariable((type as IndexedAccessType).objectType));
-    }
-
     function getConstraintOfIndexedAccess(type: IndexedAccessType) {
         return hasNonCircularBaseConstraint(type) ? getConstraintFromIndexedAccess(type) : undefined;
     }
@@ -17037,6 +17032,15 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return !!(getGenericObjectFlags(type) & ObjectFlags.IsGenericIndexType);
     }
 
+    function isConstTypeVariable(type: Type): boolean {
+        return !!(getGenericObjectFlags(type) & ObjectFlags.IsConstTypeVariable);
+    }
+
+    function isConstTypeVariableWorker(type: Type): boolean {
+        return !!(type.flags & TypeFlags.TypeParameter && some((type as TypeParameter).symbol?.declarations, d => hasSyntacticModifier(d, ModifierFlags.Const)) ||
+            type.flags & TypeFlags.IndexedAccess && isConstTypeVariableWorker((type as IndexedAccessType).objectType));
+    }
+
     function getGenericObjectFlags(type: Type): ObjectFlags {
         if (type.flags & TypeFlags.UnionOrIntersection) {
             if (!((type as UnionOrIntersectionType).objectFlags & ObjectFlags.IsGenericTypeComputed)) {
@@ -17053,7 +17057,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return (type as SubstitutionType).objectFlags & ObjectFlags.IsGenericType;
         }
         return (type.flags & TypeFlags.InstantiableNonPrimitive || isGenericMappedType(type) || isGenericTupleType(type) ? ObjectFlags.IsGenericObjectType : 0) |
-            (type.flags & (TypeFlags.InstantiableNonPrimitive | TypeFlags.Index | TypeFlags.TemplateLiteral | TypeFlags.StringMapping) && !isPatternLiteralType(type) ? ObjectFlags.IsGenericIndexType : 0);
+            (type.flags & (TypeFlags.InstantiableNonPrimitive | TypeFlags.Index | TypeFlags.TemplateLiteral | TypeFlags.StringMapping) && !isPatternLiteralType(type) ? ObjectFlags.IsGenericIndexType : 0) |
+            (isConstTypeVariableWorker(type) ? ObjectFlags.IsConstTypeVariable : 0);
     }
 
     function getSimplifiedType(type: Type, writing: boolean): Type {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index e6ce574df4a..48dfb897de2 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5922,22 +5922,24 @@ export const enum ObjectFlags {
     /** @internal */
     IsGenericIndexType = 1 << 23, // Union or intersection contains generic index type
     /** @internal */
+    IsConstTypeVariable = 1 << 24, // Union or intersection contains const type parameter
+    /** @internal */
     IsGenericType = IsGenericObjectType | IsGenericIndexType,
 
     // Flags that require TypeFlags.Union
     /** @internal */
-    ContainsIntersections = 1 << 24, // Union contains intersections
+    ContainsIntersections = 1 << 25, // Union contains intersections
     /** @internal */
-    IsUnknownLikeUnionComputed = 1 << 25, // IsUnknownLikeUnion flag has been computed
+    IsUnknownLikeUnionComputed = 1 << 26, // IsUnknownLikeUnion flag has been computed
     /** @internal */
-    IsUnknownLikeUnion = 1 << 26, // Union of null, undefined, and empty object type
+    IsUnknownLikeUnion = 1 << 27, // Union of null, undefined, and empty object type
     /** @internal */
 
     // Flags that require TypeFlags.Intersection
     /** @internal */
-    IsNeverIntersectionComputed = 1 << 24, // IsNeverLike flag has been computed
+    IsNeverIntersectionComputed = 1 << 25, // IsNeverLike flag has been computed
     /** @internal */
-    IsNeverIntersection = 1 << 25, // Intersection reduces to never
+    IsNeverIntersection = 1 << 26, // Intersection reduces to never
 }
 
 /** @internal */