WIP: Only array _errors, not all objects

Author: ciscoheat

src/lib/stringPath.ts

@@ -59,33 +59,46 @@ export type StringPath<T extends object> = NonNullable<T> extends (infer U)[]
         }[keyof T]
   : never;
 
-export type StringPathLeaves<T extends object> =
-  NonNullable<T> extends (infer U)[]
-    ? NonNullable<U> extends object
-      ? `[${number}]${NonNullable<U> extends unknown[]
-          ? ''
-          : '.'}${StringPathLeaves<NonNullable<U>> & string}`
-      : `[${number}]`
-    : NonNullable<T> extends object
+type ArrField<Arr extends string, K> = Arr extends never
+  ? never
+  : K extends string
+  ? `${K}.${Arr}`
+  : never;
+
+export type StringPathLeaves<
+  T extends object,
+  Arr extends string = never
+> = NonNullable<T> extends (infer U)[]
+  ? NonNullable<U> extends object
     ?
-        | {
-            // Same as FilterObjects but inlined for better intellisense
-            [K in keyof T]: NonNullable<T[K]> extends object
-              ? NonNullable<T[K]> extends Date | Set<unknown>
-                ? K
-                : never
-              : K;
-          }[keyof T]
-        | {
-            [K in keyof T]-?: K extends string
-              ? NonNullable<T[K]> extends object
-                ? `${K}${NonNullable<T[K]> extends unknown[]
-                    ? ''
-                    : '.'}${StringPathLeaves<NonNullable<T[K]>> & string}`
-                : never
-              : never;
-          }[keyof T]
-    : never;
+        | `[${number}].${Arr}`
+        | `[${number}]${NonNullable<U> extends unknown[]
+            ? ''
+            : '.'}${StringPathLeaves<NonNullable<U>, Arr> & string}`
+    : `[${number}]`
+  : NonNullable<T> extends object
+  ?
+      | {
+          // Same as FilterObjects but inlined for better intellisense
+          [K in keyof T]: NonNullable<T[K]> extends object
+            ? NonNullable<T[K]> extends Date | Set<unknown>
+              ? K
+              : never
+            : K;
+        }[keyof T]
+      | {
+          [K in keyof T]-?: K extends string
+            ? NonNullable<T[K]> extends object
+              ?
+                  | ArrField<Arr, K>
+                  | `${K}${NonNullable<T[K]> extends unknown[]
+                      ? ''
+                      : '.'}${StringPathLeaves<NonNullable<T[K]>, Arr> &
+                      string}`
+              : never
+            : never;
+        }[keyof T]
+  : never;
 
 export type FormPathType<T, P extends string> = P extends keyof T
   ? T[P]

src/paths.test-d.ts

@@ -92,6 +92,22 @@ test('StringPathLeaves', () => {
 
   // obj.ok should exist even though it's an object (Date)
   const p: StringPathLeaves<typeof o> = 'test[3]';
+
+  type ExtraLeaves = StringPathLeaves<typeof o, '_errors'>;
+
+  const a1: ExtraLeaves = 'test._errors';
+  const a2: ExtraLeaves = 'obj.arr._errors';
+  // @ts-expect-error incorrect path
+  const a3: ExtraLeaves = 'obj.name._errors';
+  // @ts-expect-error incorrect path
+  const a4: ExtraLeaves = 'obj._errors';
+  // @ts-expect-error incorrect path
+  const a5: ExtraLeaves = 'obj.arr[2]._errors';
+  const a6: ExtraLeaves = 'obj.arr[2]';
+  const a7: ExtraLeaves = 'obj.next._errors';
+  const a8: ExtraLeaves = 'obj.next[1].level';
+  // @ts-expect-error incorrect path
+  const a9: ExtraLeaves = 'obj.next[1]._errors';
 });
 
 test('Objects with sets', () => {