fix: make optional route parameters optional in array type

Split KnownRouteParamsArray into RequiredParamsTuple and
OptionalParamsTuple so that optional route parameters become optional
tuple elements. This allows passing fewer array items when trailing
parameters are optional, e.g. `route('posts.comments.show', [2])`.

Fixes #736

Author: pataar

src/js/index.d.ts

@@ -114,16 +114,28 @@ type RouteParamsObject<N extends RouteName> = N extends KnownRouteName
 type GenericRouteParamsArray = unknown[];
 /**
  * An array of parameters for a specific named route.
+ *
+ * Required parameters come first as required tuple elements, then optional
+ * parameters become optional tuple elements, followed by arbitrary extras.
  */
 type KnownRouteParamsArray<I extends readonly ParameterInfo[]> = [
-    ...{ [K in keyof I]: Routable<I[K]> },
-    ...unknown[],
+    ...RequiredParamsTuple<I>,
+    ...OptionalParamsTuple<I>,
 ];
-// Because `K in keyof I` for a `readonly` array is always a number, even though this
-// looks like `{ 0: T, 1: U, 2: V }` TypeScript generates `[T, U, V]`. The nested
-// array destructing lets us type the first n items in the array, which are known
-// route parameters, and then allow arbitrary additional items.
-// See https://github.com/tighten/ziggy/pull/664#discussion_r1330002370.
+
+type RequiredParamsTuple<I extends readonly ParameterInfo[]> =
+    I extends readonly [infer F extends ParameterInfo, ...infer R extends ParameterInfo[]]
+        ? F extends { required: true }
+            ? [Routable<F>, ...RequiredParamsTuple<R>]
+            : []
+        : [];
+
+type OptionalParamsTuple<I extends readonly ParameterInfo[]> =
+    I extends readonly [infer F extends ParameterInfo, ...infer R extends ParameterInfo[]]
+        ? F extends { required: false }
+            ? [Routable<F>?, ...OptionalParamsTuple<R>]
+            : OptionalParamsTuple<R>
+        : [...unknown[]];
 
 // Uncomment to test:
 // type B = KnownRouteParamsArray<[{ name: 'post'; required: true; binding: 'uuid' }]>;

tests/js/route.test-d.ts

@@ -65,12 +65,12 @@ assertType(route('posts.comments.show', 'foo'));
 assertType(route('posts.comments.show'));
 
 // Simple array examples
-// assertType(route('posts.comments.show', [2])); // TODO shouldn't error, only one required param
+assertType(route('posts.comments.show', [2]));
 assertType(route('posts.comments.show', [2, 3]));
-// assertType(route('posts.comments.show', ['foo'])); // TODO shouldn't error, only one required param
+assertType(route('posts.comments.show', ['foo']));
 assertType(route('posts.comments.show', ['foo', 'bar']));
 // Allows mix of plain values and parameter objects
-// assertType(route('posts.comments.show', [{ id: 2 }])); // TODO shouldn't error, only one required param
+assertType(route('posts.comments.show', [{ id: 2 }]));
 assertType(route('posts.comments.show', [{ id: 2 }, 3]));
 assertType(route('posts.comments.show', ['2', { uuid: 3 }]));
 assertType(route('posts.comments.show', [{ id: 2 }, { uuid: '3' }]));
@@ -105,9 +105,13 @@ assertType(route().current('missing', { foo: 1 }));
 assertType(route().current('posts.comments.show', { comment: 2 }));
 assertType(route().current('posts.comments.show', { post: 2 }));
 assertType(route().current('posts.comments.show', 2));
-// assertType(route().current('posts.comments.show', [2])); // TODO shouldn't error, only one required param
+assertType(route().current('posts.comments.show', [2]));
 assertType(route().current('posts.comments.show', 'foo'));
 
+// All-optional route with array params
+assertType(route('optional', []));
+assertType(route('optional', ['foo']));
+
 // Test route function return types
 assertType<string>(route('optional', { maybe: 'foo' }));
 assertType<string>(route('optional', 'foo'));