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feat(eslint-plugin): [prefer-optional-chain] use type checking for strict falsiness#6240

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32 changes: 29 additions & 3 deletionspackages/eslint-plugin/docs/rules/prefer-optional-chain.md
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Expand Up@@ -57,9 +57,35 @@ foo?.a?.b?.c?.d?.e;

<!--/tabs-->

:::note
There are a few edge cases where this rule will false positive. Use your best judgement when evaluating reported errors.
:::
## Options

### `looseFalsiness`

By default, this rule will ignore cases that could result with different result values when switched to optional chaining.
For example, the following `box != null && box.value` would not be flagged by default.

<!--tabs-->

### ❌ Incorrect

```ts
declare const box: { value: number } | null;
// Type: false | number
box != null && box.value;
```

### ✅ Correct

```ts
declare const box: { value: number } | null;
// Type: undefined | number
box?.value;
```

<!--/tabs-->

If you don't mind your code considering all falsy values the same (e.g. the `false` and `undefined` above), you can enable `looseFalsiness: true`.
Doing so makes the rule slightly incorrect - but speeds it by not having to ask TypeScript's type checker for information.

## When Not To Use It

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Expand Up@@ -35,6 +35,7 @@ export = {
'@typescript-eslint/non-nullable-type-assertion-style': 'off',
'@typescript-eslint/prefer-includes': 'off',
'@typescript-eslint/prefer-nullish-coalescing': 'off',
'@typescript-eslint/prefer-optional-chain': 'off',
'@typescript-eslint/prefer-readonly': 'off',
'@typescript-eslint/prefer-readonly-parameter-types': 'off',
'@typescript-eslint/prefer-reduce-type-parameter': 'off',
Expand Down
1 change: 0 additions & 1 deletionpackages/eslint-plugin/src/configs/stylistic.ts
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Expand Up@@ -24,7 +24,6 @@ export = {
'@typescript-eslint/prefer-for-of': 'error',
'@typescript-eslint/prefer-function-type': 'error',
'@typescript-eslint/prefer-namespace-keyword': 'error',
'@typescript-eslint/prefer-optional-chain': 'error',
'@typescript-eslint/sort-type-constituents': 'error',
},
};
166 changes: 97 additions & 69 deletionspackages/eslint-plugin/src/rules/prefer-optional-chain.ts
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@@ -1,5 +1,6 @@
import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
import { AST_NODE_TYPES } from '@typescript-eslint/utils';
import * as tsutils from 'ts-api-utils';
import * as ts from 'typescript';

import * as util from '../util';
Expand DownExpand Up@@ -38,19 +39,109 @@ export default util.createRule({
description:
'Enforce using concise optional chain expressions instead of chained logical ands, negated logical ors, or empty objects',
recommended: 'stylistic',
requiresTypeChecking: true,
},
hasSuggestions: true,
messages: {
preferOptionalChain:
"Prefer using an optional chain expression instead, as it's more concise and easier to read.",
optionalChainSuggest: 'Change to an optional chain.',
},
schema: [],
schema: [
{
type: 'object',
properties: {
looseFalsiness: {
description: 'Whether to consider all nullable values equivalent',
type: 'boolean',
},
},
},
],
},
defaultOptions: [],
create(context) {
defaultOptions: [
{
looseFalsiness: false,
},
],
create(context, [{ looseFalsiness }]) {
const sourceCode = context.getSourceCode();
const services = util.getParserServices(context, true);
const services = util.getParserServices(context);

interface ReportIfMoreThanOneOptions {
expressionCount: number;
initialNodeForType: TSESTree.Node;
previous: TSESTree.LogicalExpression;
optionallyChainedCode: string;
shouldHandleChainedAnds: boolean;
}

function reportIfMoreThanOne({
expressionCount,
initialNodeForType,
previous,
optionallyChainedCode,
shouldHandleChainedAnds,
}: ReportIfMoreThanOneOptions): void {
if (expressionCount <= 1) {
return;
}

if (!looseFalsiness) {
const initialType = services.getTypeAtLocation(initialNodeForType);

if (
util.isTypeFlagSet(
initialType,
ts.TypeFlags.BigIntLike |
ts.TypeFlags.Null |
ts.TypeFlags.NumberLike |
ts.TypeFlags.StringLike,
) ||
tsutils
.unionTypeParts(initialType)
.some(subType => util.isTypeIntrinsic(subType, 'false'))
) {
return;
}
}

if (
shouldHandleChainedAnds &&
previous.right.type === AST_NODE_TYPES.BinaryExpression
) {
let operator = previous.right.operator;
if (
previous.right.operator === '!==' &&
// TODO(#4820): Use the type checker to know whether this is `null`
previous.right.right.type === AST_NODE_TYPES.Literal &&
previous.right.right.raw === 'null'
) {
// case like foo !== null && foo.bar !== null
operator = '!=';
}
// case like foo && foo.bar !== someValue
optionallyChainedCode += ` ${operator} ${sourceCode.getText(
previous.right.right,
)}`;
}

context.report({
node: previous,
messageId: 'preferOptionalChain',
suggest: [
{
messageId: 'optionalChainSuggest',
fix: (fixer): TSESLint.RuleFix[] => [
fixer.replaceText(
previous,
`${shouldHandleChainedAnds ? '' : '!'}${optionallyChainedCode}`,
),
],
},
],
});
}

return {
'LogicalExpression[operator="||"], LogicalExpression[operator="??"]'(
Expand DownExpand Up@@ -187,10 +278,9 @@ export default util.createRule({

reportIfMoreThanOne({
expressionCount,
initialNodeForType: initialIdentifierOrNotEqualsExpr,
previous,
optionallyChainedCode,
sourceCode,
context,
shouldHandleChainedAnds: false,
});
},
Expand DownExpand Up@@ -271,10 +361,9 @@ export default util.createRule({

reportIfMoreThanOne({
expressionCount,
initialNodeForType: initialIdentifierOrNotEqualsExpr,
previous,
optionallyChainedCode,
sourceCode,
context,
shouldHandleChainedAnds: true,
});
},
Expand DownExpand Up@@ -472,67 +561,6 @@ const ALLOWED_NON_COMPUTED_PROP_TYPES: ReadonlySet<AST_NODE_TYPES> = new Set([
AST_NODE_TYPES.PrivateIdentifier,
]);

interface ReportIfMoreThanOneOptions {
expressionCount: number;
previous: TSESTree.LogicalExpression;
optionallyChainedCode: string;
sourceCode: Readonly<TSESLint.SourceCode>;
context: Readonly<
TSESLint.RuleContext<
'preferOptionalChain' | 'optionalChainSuggest',
never[]
>
>;
shouldHandleChainedAnds: boolean;
}

function reportIfMoreThanOne({
expressionCount,
previous,
optionallyChainedCode,
sourceCode,
context,
shouldHandleChainedAnds,
}: ReportIfMoreThanOneOptions): void {
if (expressionCount > 1) {
if (
shouldHandleChainedAnds &&
previous.right.type === AST_NODE_TYPES.BinaryExpression
) {
let operator = previous.right.operator;
if (
previous.right.operator === '!==' &&
// TODO(#4820): Use the type checker to know whether this is `null`
previous.right.right.type === AST_NODE_TYPES.Literal &&
previous.right.right.raw === 'null'
) {
// case like foo !== null && foo.bar !== null
operator = '!=';
}
// case like foo && foo.bar !== someValue
optionallyChainedCode += ` ${operator} ${sourceCode.getText(
previous.right.right,
)}`;
}

context.report({
node: previous,
messageId: 'preferOptionalChain',
suggest: [
{
messageId: 'optionalChainSuggest',
fix: (fixer): TSESLint.RuleFix[] => [
fixer.replaceText(
previous,
`${shouldHandleChainedAnds ? '' : '!'}${optionallyChainedCode}`,
),
],
},
],
});
}
}

interface NormalizedPattern {
invalidOptionallyChainedPrivateProperty: boolean;
expressionCount: number;
Expand Down
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