fix: Remove too narrow instanceof

src/typechecker/visitor/shared/function.ts

@@ -81,7 +81,7 @@ async function visitUntypedFunction(
 		params.push({
 			name,
 			pType,
-			isGeneric: pType instanceof GenericType,
+			isGeneric: pType.isGeneric(),
 			isOptional,
 		});
 	}

src/types/GenericType.ts

@@ -35,6 +35,10 @@ export class GenericType extends Type {
 		return this;
 	}
 
+	public override isGeneric(): boolean {
+		return true;
+	}
+
 	public static create(label: string, aliasType?: Type): GenericType {
 		return new GenericType(label, aliasType ?? UnknownType.create());
 	}

src/types/Type.ts

@@ -16,4 +16,8 @@ export abstract class Type {
 	public replaceGenerics(_generics: { name: string; gType: Type }[]): Type {
 		return this;
 	}
+
+	public isGeneric(): boolean {
+		return false;
+	}
 }

src/types/UnionType.ts

@@ -74,6 +74,10 @@ export class UnionType extends Type {
 		return new UnionType(this.types.map((t) => t.replaceGenerics(generics))).simplify();
 	}
 
+	public override isGeneric(): boolean {
+		return this.types.some((t) => t.isGeneric());
+	}
+
 	public get size(): number {
 		return this.types.length;
 	}