feat: support narrowing by deep object keys in NarrowPartial

Author: ethanresnick

src/util/type-utils.ts

@@ -1,8 +1,8 @@
-import type { InsertResult } from '../query-builder/insert-result.js'
 import type { DeleteResult } from '../query-builder/delete-result.js'
+import type { InsertResult } from '../query-builder/insert-result.js'
+import type { MergeResult } from '../query-builder/merge-result.js'
 import type { UpdateResult } from '../query-builder/update-result.js'
 import type { KyselyTypeError } from './type-error.js'
-import type { MergeResult } from '../query-builder/merge-result.js'
 
 /**
  * Given a database type and a union of table names in that db, returns
@@ -153,19 +153,25 @@ export type Equals<T, U> =
     ? true
     : false
 
-export type NarrowPartial<O, T> = DrainOuterGeneric<
-  T extends object
-    ? {
-        [K in keyof O & string]: K extends keyof T
-          ? T[K] extends NotNull
-            ? Exclude<O[K], null>
+export type NarrowPartial<O, T> = T extends object
+  ? DrainOuterGeneric<{
+      [K in keyof O & string]: K extends keyof T
+        ? T[K] extends NotNull
+          ? Exclude<O[K], null>
+          : T[K] extends object
+            ? SimplifyDeep<O[K] & NarrowPartial<O[K], T[K]>>
             : T[K] extends O[K]
               ? T[K]
               : KyselyTypeError<`$narrowType() call failed: passed type does not exist in '${K}'s type union`>
-          : O[K]
-      }
-    : never
->
+        : O[K]
+    }>
+  : never
+
+type SimplifyDeep<T> = T extends object
+  ? T extends Date | RegExp | Map<unknown, unknown> | Set<unknown>
+    ? T
+    : DrainOuterGeneric<{ [K in keyof T]: SimplifyDeep<T[K]> } & {}>
+  : T
 
 /**
  * A type constant for marking a column as not null. Can be used with `$narrowPartial`.

test/typings/shared.d.ts

@@ -80,6 +80,12 @@ export interface PersonMetadata {
     }
     tags: string[]
   }>
+  discriminatedUnionProfile: JSONColumnType<{
+    auth:
+      | { type: 'token'; token: string }
+      | { type: 'session'; session_id: string }
+    tags: string[]
+  }>
   experience: JSONColumnType<
     {
       establishment: string

test/typings/test-d/select.test-d.ts

@@ -1,3 +1,4 @@
+import { expectError, expectType } from 'tsd'
 import {
   type Expression,
   type ExpressionWrapper,
@@ -9,7 +10,6 @@ import {
   sql,
 } from '..'
 import type { Database, Person } from '../shared'
-import { expectType, expectError } from 'tsd'
 
 async function testSelectSingle(db: Kysely<Database>) {
   const qb = db.selectFrom('person')
@@ -115,6 +115,11 @@ async function testSelectSingle(db: Kysely<Database>) {
     .$narrowType<NarrowTarget>()
     .execute()
 
+  expectType<
+    | { callback_url: string; queue_id: null }
+    | { callback_url: null; queue_id: string }
+  >(r15)
+
   // Narrow not null
   const [r16] = await db
     .selectFrom('action')
@@ -134,6 +139,20 @@ async function testSelectSingle(db: Kysely<Database>) {
   expectType<string>(r17.callback_url)
   expectType<string>(r17.queue_id)
 
+  // Narrow discriminated union
+  const [r18] = await db
+    .selectFrom('person_metadata')
+    .select(['discriminatedUnionProfile'])
+    .$narrowType<{ discriminatedUnionProfile: { auth: { type: 'token' } } }>()
+    .execute()
+
+  expectType<{
+    discriminatedUnionProfile: {
+      auth: { type: 'token'; token: string }
+      tags: string[]
+    }
+  }>(r18)
+
   const expr1 = db.selectFrom('person').select('first_name').$asScalar()
   expectType<ExpressionWrapper<Database, 'person', string>>(expr1)