Prevent the .not modifier from being chained (#20)

mmkal · Nov 29, 2022 · a335a12 · a335a12
1 parent dcd6422
commit a335a12
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Showing 2 changed files with 6 additions and 1 deletion.
diff --git a/src/index.ts b/src/index.ts
@@ -143,7 +143,7 @@ export interface ExpectTypeOf<Actual, B extends boolean> {
       ? never
       : ExpectTypeOf<T, B>
     : never
-  not: ExpectTypeOf<Actual, Not<B>>
+  not: Omit<ExpectTypeOf<Actual, Not<B>>, 'not'>
 }
 const fn: any = () => true
 

diff --git a/test/types.test.ts b/test/types.test.ts
@@ -70,6 +70,11 @@ test(`never types don't sneak by`, () => {
   expectTypeOf<never>().toMatchTypeOf<{foo: string}>()
 })
 
+test('not cannot be chained', () => {
+  // @ts-expect-error
+  expectTypeOf<number>().not.not.toBeNumber()
+})
+
 test('constructor params', () => {
   // The built-in ConstructorParameters type helper fails to pick up no-argument overloads.
   // This test checks that's still the case to avoid unnecessarily maintaining a workaround,