ramda: add generic typing to Evolver (#41672)

* Add generic typing to Evolver

* Remove partial import

* Fix lint issue

types/ramda/test/evolve-tests.ts

@@ -58,4 +58,31 @@ import * as R from 'ramda';
   });
 
   const ex3Test: { a: { b: string; c: null; d: { e: string } } } = ex3;
+
+  // Evolver with a generic:
+
+  const ev1: R.Evolver<{ a: string }> = { a: R.always("b") };
+
+  // Evolver supports partial transformation:
+
+  const ev2: R.Evolver<{ a: string, b: boolean }> = { b: (b: boolean) => true };
+
+  // Evolver disallows unknown prop:
+
+  // $ExpectError
+  const ev3: R.Evolver<{ a: string }> = { b: R.not };
+
+  // Typed Evolver disallows nesting:
+
+  const ev4: R.Evolver<{ a: { b: boolean } }> = { a: { b: R.not } };
+
+  // Evolver disallows nesting for primitives:
+
+  // $ExpectError
+  const ev5: R.Evolver<{ a: string }> = { a: { b: R.not } };
+
+  // Evolver needs function:
+
+  // $ExpectError
+  const ev6: R.Evolver = { a: 1 };
 };

types/ramda/tools.d.ts

@@ -174,11 +174,13 @@ type Evolved<A> =
       : never;
 
 /**
- * <needs description>
+ * A set of transformation to run as part of an evolve
+ * @param T - the type to be evolved
  */
-export interface Evolver {
-    [key: string]: ((value: any) => any) | Evolver;
-}
+export type Evolver<T extends Evolvable<any> = any> = {
+    // if T[K] isn't evolvable, don't allow nesting for that property
+    [key in keyof Partial<T>]: ((value: T[key]) => T[key]) | (T[key] extends Evolvable<any> ? Evolver<T[key]> : never);
+};
 
 /**
  * <needs description>