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Fix choose directive type inference #4240

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Merged
augustjk merged 10 commits into from
Oct 27, 2023
Merged

Fix choose directive type inference #4240

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91c85cb
Add third type parameter to choose.ts
remziatay Sep 28, 2023
9385cf1
Add regression test
remziatay Sep 29, 2023
840258f
Add changeset
remziatay Sep 29, 2023
34cb244
Wrap type-only test with test.skip
augustjk Oct 27, 2023
a75f49f
Add more detail to changelog
augustjk Oct 27, 2023
bf7bf4d
Merge branch 'main' of https://github.com/lit/lit into patch-4
augustjk Oct 27, 2023
3afa4bf
Fix typo in test description
augustjk Oct 27, 2023
83f560a
Update .changeset/good-grapes-double.md
augustjk Oct 27, 2023
78a39af
Merge branch 'main' into patch-4
augustjk Oct 27, 2023
5f0a5ba
Add 'lit' package to changeset
augustjk Oct 27, 2023
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6 changes: 6 additions & 0 deletions .changeset/good-grapes-double.md
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@@ -0,0 +1,6 @@
---
'lit-html': patch
'lit': patch
---

Improved the type inferece of the `choose()` directive to properly restrict the case type inferred from provided value. **Note**: If this change creates a type error in your code, there must have been an unreachable case that can be removed, or the type of your `value` might be missing a valid case in the union.
4 changes: 2 additions & 2 deletions packages/lit-html/src/directives/choose.ts
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Expand Up @@ -29,9 +29,9 @@
* }
* ```
*/
export const choose = <T, V>(
export const choose = <T, V, K extends T = T>(
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@rictic rictic Sep 28, 2023

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Nice! Yeah this fixes the issue. Playground demo

value: T,
cases: Array<[T, () => V]>,
cases: Array<[K, () => V]>,
defaultCase?: () => V
) => {
for (const c of cases) {
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14 changes: 14 additions & 0 deletions packages/lit-html/src/test/directives/choose_test.ts
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Expand Up @@ -45,4 +45,18 @@ suite('choose', () => {
'C'
);
});

// Type-only regression test of https://github.com/lit/lit/issues/4220
test.skip('type-only: correctly infers type of possible cases from value', () => {
type CheckoutStep = 'register' | 'delivery' | 'payment';
const step = 'register' as CheckoutStep;
return choose(step, [
// @ts-expect-error 'test' is not assignable to 'CheckoutStep'
['test', () => 1],
// @ts-expect-error 'random' is not assignable to 'CheckoutStep'
['random', () => 2],
// This should compile fine
['register', () => 3],
]);
});
});