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fix(eslint-plugin): [prefer-optional-chain] should report case that can be converted to optional void function call ?.() #11272

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fix(eslint-plugin): [prefer-optional-chain] should report case that can be converted to optional void function call ?.() #11272

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aec9ef5
feat: add check void option
nayounsang Jun 5, 2025
e35a6f2
test: add test case for check void
nayounsang Jun 5, 2025
eacc622
feat: check void type
nayounsang Jun 5, 2025
88decc1
chore: add snapshot
nayounsang Jun 5, 2025
4171c5e
docs: add checkvoid section
nayounsang Jun 5, 2025
791461b
chore: update snapshot
nayounsang Jun 5, 2025
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31 changes: 31 additions & 0 deletions packages/eslint-plugin/docs/rules/prefer-optional-chain.mdx
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Expand Up @@ -265,6 +265,37 @@ thing?.toString();
</TabItem>
</Tabs>

### `checkVoid`

{/* insert option description */}

Examples of code for this rule with `{ checkVoid: true }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "checkVoid": true }'
declare const thing: {
method: undefined | (() => void);
};

thing.method && thing.method();
```

</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "checkVoid": true }'
declare const thing: {
method: undefined | (() => void);
};

thing.method?.();
```

</TabItem>
</Tabs>

### `requireNullish`

{/* insert option description */}
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1 change: 1 addition & 0 deletions packages/eslint-plugin/src/rules/prefer-optional-chain-utils/PreferOptionalChainOptions.ts
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Expand Up @@ -10,5 +10,6 @@ export interface PreferOptionalChainOptions {
checkNumber?: boolean;
checkString?: boolean;
checkUnknown?: boolean;
checkVoid?: boolean;
requireNullish?: boolean;
}
5 changes: 5 additions & 0 deletions packages/eslint-plugin/src/rules/prefer-optional-chain-utils/gatherLogicalOperands.ts
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Expand Up @@ -111,6 +111,11 @@ function isValidFalseBooleanCheckType(
if (options.checkBigInt === true) {
allowedFlags |= ts.TypeFlags.BigIntLike;
}

if (options.checkVoid === true) {
allowedFlags |= ts.TypeFlags.Void;
}

return types.every(t => isTypeFlagSet(t, allowedFlags));
}
Comment on lines 111 to 120
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I'm wondering if this section should be flipped to only specify the flags that aren't checked instead of the ones that are?

For now, no tests fail if I switch the logic to the following, where we don't bother with explicit options for or handling of void:

  let flagsToExcludeFromCheck = 0;
  if (options.checkAny !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.Any;
  }
  if (options.checkUnknown !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.Unknown;
  }
  if (options.checkString !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.StringLike;
  }
  if (options.checkNumber !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.NumberLike;
  }
  if (options.checkBoolean !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.BooleanLike;
  }
  if (options.checkBigInt !== true) {
    flagsToExcludeFromCheck |= ts.TypeFlags.BigIntLike;
  }

  return !types.some(t => isTypeFlagSet(t, flagsToExcludeFromCheck));

Can we come up with some test cases that would

  • demonstrate which approach is preferable
  • solidify that approach rather than passing with either choice of logic

I haven't thought deeply about which logic makes more sense, so it would be lovely if you have time to give this some thought and justify with examples which way is preferable. Thanks!

For reference, I ask this because:

  • prefer-nullish-coalescing does have the "only ignore specific types" approach, rather than "only check some hardcoded types plus allowed primitives" as in the existing implementation of this rule.
  • the answer will determine whether creation of a new option is warranted

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@nayounsang nayounsang Jun 7, 2025 •
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I will think about it more as I work, but I will leave a quick comment first. The more immediate the communication, the better. Even if it's not accurate!

  1. I would recommend adding void options. My philosophy is that the more open source users can customize with options, the more use cases users can cover. (Adding options would likely require some additional documentation changes beyond the current commit.)
  2. Since the defaults are given as true, it seems more natural to change to the suggested code. Even better, it prevents optional chaining from being skipped on unexpected types.
  3. I guess I need to consider side effects when flagsToExcludeFromCheck = 0.
let allowedFlags = NULLISH_FLAGS | ts.TypeFlags.Object;

All tests will pass if flagsToExcludeFromCheck = 0 for now and I don't think there's a problem at all.(Due to 2), but something feels off because allowedFlags has default value...

Perhaps the test case would be to determine what error/suggestion occurs depending on whether the option is turned off.


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6 changes: 6 additions & 0 deletions packages/eslint-plugin/src/rules/prefer-optional-chain.ts
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Expand Up @@ -82,6 +82,11 @@ export default createRule<
description:
'Check operands that are typed as `unknown` when inspecting "loose boolean" operands.',
},
checkVoid: {
type: 'boolean',
description:
'Check operands that are typed as `void` when inspecting "loose boolean" operands.',
},
requireNullish: {
type: 'boolean',
description:
Expand All @@ -100,6 +105,7 @@ export default createRule<
checkNumber: true,
checkString: true,
checkUnknown: true,
checkVoid: true,
requireNullish: false,
},
],
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19 changes: 19 additions & 0 deletions packages/eslint-plugin/tests/docs-eslint-output-snapshots/prefer-optional-chain.shot
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16 changes: 16 additions & 0 deletions packages/eslint-plugin/tests/rules/prefer-optional-chain/prefer-optional-chain.test.ts
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Expand Up @@ -1680,6 +1680,22 @@ describe('hand-crafted cases', () => {
],
output: 'a?.prop;',
},
// check void
{
code: `
declare const foo: {
method: undefined | (() => void);
};
foo.method && foo.method();
`,
errors: [{ messageId: 'preferOptionalChain' }],
output: `
declare const foo: {
method: undefined | (() => void);
};
foo.method?.();
`,
},
],
valid: [
'!a || !b;',
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6 changes: 6 additions & 0 deletions packages/eslint-plugin/tests/schema-snapshots/prefer-optional-chain.shot
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