Fix array concatenation bug

Author: supermacro

src/utils.ts

@@ -21,6 +21,21 @@ type ExtractErrAsyncTypes<T extends readonly ResultAsync<unknown, unknown>[]> =
   [idx in keyof T]: T[idx] extends ResultAsync<unknown, infer E> ? E : never
 }
 
+
+const appendValueToEndOfList = <T>(value: T) => (list: T[]): T[] => {
+  // need to wrap `value` inside of an array in order to prevent
+  // Array.prototype.concat from destructuring the contents of `value`
+  // into `list`.
+  //
+  // Otherwise you will receive [ 'hi', 1, 2, 3 ]
+  // when you actually expected a tuple containing [ 'hi', [ 1, 2, 3 ] ]
+  if (Array.isArray(value)) {
+    return list.concat([ value ])
+  }
+
+  return list.concat(value)
+}
+
 /**
  * Short circuits on the FIRST Err value that we find
  */
@@ -30,7 +45,7 @@ const combineResultList = <T, E>(resultList: Result<T, E>[]): Result<T[], E> =>
       acc.isOk()
         ? result.isErr()
           ? err(result.error)
-          : acc.map((values) => values.concat(result.value))
+          : acc.map(appendValueToEndOfList(result.value))
         : acc,
     ok([]) as Result<T[], E>,
   )

tests/index.test.ts

@@ -393,6 +393,24 @@ describe('Utils', () => {
 
         expect(result._unsafeUnwrap()).toEqual(['Yooooo', 123, true])
       })
+
+      it('Does not destructure / concatenate arrays', () => {
+        type HomogenousList = [
+          Result<string[], boolean>,
+          Result<number[], string>,
+        ]
+
+        const homogenousList: HomogenousList = [
+          ok(['hello', 'world']),
+          ok([1, 2, 3])
+        ]
+
+        type ExpectedResult = Result<[ string[], number[] ], boolean | string>
+
+        const result: ExpectedResult = combine(homogenousList)
+
+        expect(result._unsafeUnwrap()).toEqual([ [ 'hello', 'world' ], [ 1, 2, 3 ]])
+      })
     })
 
     describe('Async `combine`', () => {
@@ -424,19 +442,25 @@ describe('Utils', () => {
       })
 
       it('Combines heterogeneous lists', async () => {
-        type HeterogenousList = [ ResultAsync<string, string>, ResultAsync<number, number>, ResultAsync<boolean, boolean> ]
+        type HeterogenousList = [
+          ResultAsync<string, string>,
+          ResultAsync<number, number>,
+          ResultAsync<boolean, boolean>,
+          ResultAsync<number[], string>,
+        ]
 
         const heterogenousList: HeterogenousList = [
           okAsync('Yooooo'),
           okAsync(123),
           okAsync(true),
+          okAsync([ 1, 2, 3]),
         ]
 
-        type ExpecteResult = Result<[ string, number, boolean ], string | number | boolean>
+        type ExpecteResult = Result<[ string, number, boolean, number[] ], string | number | boolean>
 
-        const result: ExpecteResult= await combine(heterogenousList)
+        const result: ExpecteResult = await combine(heterogenousList)
 
-        expect(result._unsafeUnwrap()).toEqual(['Yooooo', 123, true])
+        expect(result._unsafeUnwrap()).toEqual(['Yooooo', 123, true, [ 1, 2, 3 ]])
       })
     })
   })