Improve or types

jmurphyau · Sep 11, 2023 · f9741c5 · f9741c5
1 parent e93e494
commit f9741c5
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Showing 3 changed files with 18 additions and 1 deletion.
diff --git a/packages/ember-truth-helpers/src/helpers/or.ts b/packages/ember-truth-helpers/src/helpers/or.ts
@@ -1,4 +1,5 @@
 import truthConvert, {
+  Falsy,
   MaybeTruthy,
   TruthConvert,
 } from '../utils/truth-convert.ts';
@@ -11,7 +12,7 @@ type FirstTruthy<T> = T extends [infer Item]
     ? Head
     : TruthConvert<Head> extends false
     ? FirstTruthy<Tail>
-    : NonNullable<Head> | FirstTruthy<Tail>
+    : Exclude<Head, Falsy> | FirstTruthy<Tail>
   : undefined;
 
 interface OrSignature<T extends MaybeTruthy[]> {

diff --git a/packages/ember-truth-helpers/src/utils/truth-convert.ts b/packages/ember-truth-helpers/src/utils/truth-convert.ts
@@ -1,9 +1,22 @@
 import { isArray } from '@ember/array';
 
+export type Falsy =
+  | { isTruthy: false }
+  | undefined
+  | null
+  | false
+  | 0
+  | -0
+  | 0n
+  | ''
+  | never[];
+
 type ConvertTruthyObject<T> = T extends { isTruthy: infer U } ? U : T;
 
 // We check here in the order of the following function to maintain parity
 // Note that this will not handle EmberArray correctly.
+// We don't use Falsy since we want to be able to more definitively determine
+// truthy results.
 type _TruthConvert<T> = T extends { isTruthy: true }
   ? true
   : T extends { isTruthy: false }

diff --git a/packages/ember-truth-helpers/type-tests/helpers/or.test.ts b/packages/ember-truth-helpers/type-tests/helpers/or.test.ts
@@ -29,3 +29,6 @@ expectTypeOf(computeOr(foo, 1)).toEqualTypeOf(foo);
 
 let maybeString: string | undefined;
 expectTypeOf(computeOr(maybeString, 'foo')).toEqualTypeOf<string>();
+
+const numberOrFalse = 1 as number | false;
+expectTypeOf(computeOr(numberOrFalse, 'foo')).toEqualTypeOf<number | 'foo'>();