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docs(website): add non-null asserted optional chain Prettier divergence #1066

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Dec 6, 2023
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docs(website): add non-null asserted optional chain Prettier divergence #1066

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docs(website): add non-null asserted optional chain Prettier divergence
Conaclos Dec 5, 2023
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Update website/src/content/docs/formatter/index.mdx
ematipico Dec 6, 2023
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32 changes: 32 additions & 0 deletions website/src/content/docs/formatter/index.mdx
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Expand Up @@ -183,6 +183,38 @@ Diff
```


### Prettier has an inconsistent behavior for parenthesized non-null-asserted optional chains

In _TypeScript_, the non-null assertion operator `!` allows asserting that a value is non-null.
When applied on an optional chain, the assertion applies to the entire chain regardless of the presence of parentheses,
making equivalent `(a.?.b)!` and `a.?.b!`.

The previous code examples are already well-formatted, according to Prettier.
Prettier is used to enforce the presence or the absence of parentheses.
This looks like a missed opportunity to normalize the code.

Moreover, Prettier doesn't remove the parentheses even when they enclose the non-null assertion.
Instead, it moves the operator outside the parentheses.

Input:

```ts title="example.ts"
a.?.b!
(a.?.b)!
(a.?.b!)
```

Diff

```ts title="example.ts" del={2, 4} ins={3, 5}
a.?.b!
(a.?.b)!
a.?.b!
(a.?.b)!
a.?.b!
```


### Prettier formats invalid syntaxes

Prettier's Babel-based parsing for JavaScript and TypeScript is very loose and [allows multiple errors](https://github.com/prettier/prettier/blob/e4a74c05f4502dd4ec70495c3130ff08ab088e05/src/language-js/parse/babel.js#L177-L218) to be ignored.
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