From 9b4036d1fda25586a5866c8e77ba698f39d709f9 Mon Sep 17 00:00:00 2001
From: Beeno Tung <aabbcc1241@yahoo.com.hk>
Date: Mon, 30 Oct 2023 08:19:23 +0800
Subject: [PATCH] wip: recursively infer parser return type

---
 examples/infer-demo.ts |  7 +++++--
 src/core.spec.ts       | 13 ++++++++++++-
 src/core.ts            |  8 ++++----
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/examples/infer-demo.ts b/examples/infer-demo.ts
index 4e81f9a..4ddf9ca 100644
--- a/examples/infer-demo.ts
+++ b/examples/infer-demo.ts
@@ -29,7 +29,10 @@ console.log(parser.type)
 
 type Result = ParseResult<typeof parser>
 type Post = Result['postList'][number]
-// @ts-expect-error
 type PostStatus = Post['status']
 
-// TODO extract object field name without $suffix
+function checkType<T>(t: T) {
+  /* noop */
+}
+
+checkType<'active' | 'hidden'>(null as unknown as PostStatus)
diff --git a/src/core.spec.ts b/src/core.spec.ts
index 97ce951..65f1ad6 100644
--- a/src/core.spec.ts
+++ b/src/core.spec.ts
@@ -461,7 +461,7 @@ describe('object parser', () => {
 }`)
     }
   })
-  it('should infer result type without $ flags', () => {
+  it('should infer result type without enums/nullable/optional flags', () => {
     let parser = inferFromSampleValue({
       'status_1$enums': ['a' as const, 'b' as const],
       'status_2$enum': ['a' as const, 'b' as const],
@@ -500,6 +500,17 @@ describe('object parser', () => {
       status_11?: undefined | null | 'a' | 'b'
     }>(result)
   })
+  it('should recursively infer result type', () => {
+    let parser = inferFromSampleValue({
+      a$nullable: {
+        b$optional: {
+          c$enums: ['a' as const, 'b' as const],
+        },
+      },
+    })
+    let result = parser.parse({ a: { b: { c: 'a' } } })
+    expect(result.a?.b?.c).to.equals('a')
+  })
 })
 
 describe('date parser', () => {
diff --git a/src/core.ts b/src/core.ts
index 9530614..614c697 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -1097,13 +1097,13 @@ type InferNullableField<O> = {
     ? never
     : P extends `${string}$null${string}`
     ? never
-    : P]: O[P]
+    : P]: InferType<O[P]>
 } & {
   [P in keyof O as P extends `${infer H}$nullable${infer T}`
     ? `${H}${T}`
     : P extends `${infer H}$null${infer T}`
     ? `${H}${T}`
-    : never]: null | O[P]
+    : never]: null | InferType<O[P]>
 }
 
 type InferOptionalField<O> = {
@@ -1111,13 +1111,13 @@ type InferOptionalField<O> = {
     ? never
     : P extends `${string}?${string}`
     ? never
-    : P]: O[P]
+    : P]: InferType<O[P]>
 } & {
   [P in keyof O as P extends `${infer H}$optional${infer T}`
     ? `${H}${T}`
     : P extends `${infer H}?${infer T}`
     ? `${H}${T}`
-    : never]?: O[P]
+    : never]?: InferType<O[P]>
 }
 
 type InferObjectType<T> = InferOptionalField<