tweak cache key

Author: Andarist

src/compiler/checker.ts

@@ -20374,16 +20374,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             error(currentNode, Diagnostics.Type_instantiation_is_excessively_deep_and_possibly_infinite);
             return errorType;
         }
-        mapper.instantiations ??= new Map();
-        const cached = mapper.instantiations.get(type.id);
+        const key = type.id + getAliasId(aliasSymbol, aliasTypeArguments);
+        const cached = (mapper.instantiations ??= new Map()).get(key);
         if (cached) {
             return cached;
         }
         totalInstantiationCount++;
         instantiationCount++;
         instantiationDepth++;
         const result = instantiateTypeWorker(type, mapper, aliasSymbol, aliasTypeArguments);
-        mapper.instantiations.set(type.id, result);
+        mapper.instantiations.set(key, result);
         instantiationDepth--;
         return result;
     }

src/compiler/types.ts

@@ -7029,11 +7029,11 @@ export const enum TypeMapKind {
 
 /** @internal */
 export type TypeMapper =
-    | { kind: TypeMapKind.Simple; source: Type; target: Type; instantiations?: Map<TypeId, Type>; }
-    | { kind: TypeMapKind.Array; sources: readonly Type[]; targets: readonly Type[] | undefined; instantiations?: Map<TypeId, Type>; }
-    | { kind: TypeMapKind.Deferred; sources: readonly Type[]; targets: (() => Type)[]; instantiations?: Map<TypeId, Type>; }
-    | { kind: TypeMapKind.Function; func: (t: Type) => Type; debugInfo?: () => string; instantiations?: Map<TypeId, Type>; }
-    | { kind: TypeMapKind.Composite | TypeMapKind.Merged; mapper1: TypeMapper; mapper2: TypeMapper; instantiations?: Map<TypeId, Type>; };
+    | { kind: TypeMapKind.Simple; source: Type; target: Type; instantiations?: Map<string, Type>; }
+    | { kind: TypeMapKind.Array; sources: readonly Type[]; targets: readonly Type[] | undefined; instantiations?: Map<string, Type>; }
+    | { kind: TypeMapKind.Deferred; sources: readonly Type[]; targets: (() => Type)[]; instantiations?: Map<string, Type>; }
+    | { kind: TypeMapKind.Function; func: (t: Type) => Type; debugInfo?: () => string; instantiations?: Map<string, Type>; }
+    | { kind: TypeMapKind.Composite | TypeMapKind.Merged; mapper1: TypeMapper; mapper2: TypeMapper; instantiations?: Map<string, Type>; };
 
 // dprint-ignore
 export const enum InferencePriority {