Merge pull request #73 from remnantkevin/fix-json-type-inference

Fix typing of `json` runtype output

Author: hoeck

src/json.ts

@@ -24,8 +24,8 @@ export const jsonRuntype = internalRuntype<unknown>((v, failOrThrow) => {
 /**
  * A String that is valid json
  */
-export function json<T>(rt: Runtype<any>): Runtype<T> {
-  return internalRuntype<T>((v, failOrThrow) => {
+export function json<T>(rt: Runtype<T>): Runtype<T> {
+  return internalRuntype<any>((v, failOrThrow) => {
     const n = (jsonRuntype as InternalRuntype)(v, failOrThrow)
 
     if (isFail(n)) {

test-d/json.test-d.ts

@@ -0,0 +1,27 @@
+import { expectType } from 'tsd'
+import * as st from '../src'
+
+const data: unknown = null
+
+// basic
+{
+  // number
+  const jsonNumberRt = st.json(st.number())
+
+  expectType<number>(jsonNumberRt(data))
+
+  // string
+  const jsonStringRt = st.json(st.string())
+
+  expectType<string>(jsonStringRt(data))
+
+  // array
+  const jsonArrayRt = st.json(st.array(st.number()))
+
+  expectType<number[]>(jsonArrayRt(data))
+
+  // object
+  const jsonObjectRt = st.json(st.record({ a: st.string() }))
+
+  expectType<{ a: string }>(jsonObjectRt(data))
+}

test-d/record.test-d.ts

@@ -35,3 +35,18 @@ const data: unknown = null
 
   expectType<{ a: { b: { c: string } } }>(rt(data))
 }
+
+// record with json
+{
+  const rt = st.record({
+    a: st.string(),
+    b: st.json(
+      st.record({
+        c: st.string(),
+      }),
+    ),
+    d: st.string(),
+  })
+
+  expectType<{ a: string; b: { c: string }; d: string }>(rt(data))
+}