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WIP: feat(eslint-plugin): [consistent-type-assertion] add allowAsReturn option #1628

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WIP: feat(eslint-plugin): [consistent-type-assertion] add allowAsReturn option #1628

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16 changes: 15 additions & 1 deletion packages/eslint-plugin/docs/rules/consistent-type-assertions.md
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Original file line number Diff line number Diff line change
Expand Up @@ -12,15 +12,18 @@ Type assertions are also commonly referred as "type casting" in TypeScript (even
type Options =
| {
assertionStyle: 'as' | 'angle-bracket';
objectLiteralTypeAssertions: 'allow' | 'allow-as-parameter' | 'never';
objectLiteralTypeAssertions?: 'allow' | 'allow-as-parameter' | 'never';
allowAsReturn?: boolean;
Comment on lines +15 to +16
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this shouldn't be a separate boolean flag.
It would be better to accept an array of strings, i.e.:

type Options = 
  | {
    assertionStyle: 'as' | 'angle-bracket';
    objectLiteralTypeAssertions?:
      | 'allow'
      | 'allow-as-parameter'
      | 'allow-as-return'
      | 'never'
      | ('allow-as-parameter' | 'allow-as-return')[];
  }
  | {
    assertionStyle: 'never';
  }

}
| {
assertionStyle: 'never';
allowAsReturn?: boolean;
};

const defaultOptions: Options = {
assertionStyle: 'as',
objectLiteralTypeAssertions: 'allow',
allowAsReturn: false,
};
```

Expand All @@ -44,10 +47,15 @@ The compiler will warn for excess properties with this syntax, but not missing _

The const assertion `const x = { foo: 1 } as const`, introduced in TypeScript 3.4, is considered beneficial and is ignored by this option.

### `allowAsReturn`

Allow type assertions on object literals if they are in a return statement.

Examples of **incorrect** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'never' }` (and for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'allow-as-parameter' }`)

```ts
const x = { ... } as T;
return {} as T;
```

Examples of **correct** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'never' }`.
Expand All @@ -69,6 +77,12 @@ new Clazz({ ... } as T);
function foo() { throw { bar: 5 } as Foo }
```

Examples of **correct** code for `{ assertionStyle: 'as', objectLiteralTypeAssertions: 'allow-as-parameter', allowAsReturn: true }`.

```ts
return {} as T;
```

## When Not To Use It

If you do not want to enforce consistent type assertions.
Expand Down
13 changes: 13 additions & 0 deletions packages/eslint-plugin/src/rules/consistent-type-assertions.ts
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Expand Up @@ -15,9 +15,11 @@ type OptUnion =
| {
assertionStyle: 'as' | 'angle-bracket';
objectLiteralTypeAssertions?: 'allow' | 'allow-as-parameter' | 'never';
allowAsReturn?: boolean;
}
| {
assertionStyle: 'never';
allowAsReturn?: boolean;
};
type Options = [OptUnion];

Expand Down Expand Up @@ -45,6 +47,7 @@ export default util.createRule<Options, MessageIds>({
assertionStyle: {
enum: ['never'],
},
allowAsReturn: { type: 'boolean' },
},
additionalProperties: false,
required: ['assertionStyle'],
Expand All @@ -58,6 +61,7 @@ export default util.createRule<Options, MessageIds>({
objectLiteralTypeAssertions: {
enum: ['allow', 'allow-as-parameter', 'never'],
},
allowAsReturn: { type: 'boolean' },
},
additionalProperties: false,
required: ['assertionStyle'],
Expand All @@ -70,6 +74,7 @@ export default util.createRule<Options, MessageIds>({
{
assertionStyle: 'as',
objectLiteralTypeAssertions: 'allow',
allowAsReturn: false,
},
],
create(context, [options]) {
Expand Down Expand Up @@ -131,6 +136,14 @@ export default util.createRule<Options, MessageIds>({
return;
}

if (
options.allowAsReturn &&
node.parent &&
node.parent.type === AST_NODE_TYPES.ReturnStatement
) {
return;
}

if (
checkType(node.typeAnnotation) &&
node.expression.type === AST_NODE_TYPES.ObjectExpression
Expand Down
29 changes: 29 additions & 0 deletions packages/eslint-plugin/tests/rules/consistent-type-assertions.test.ts
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Expand Up @@ -41,6 +41,9 @@ function foo() { throw <Foo>{ bar: 5 } }
print?.(<Foo>{ bar: 5 })
print?.call(<Foo>{ bar: 5 })
`;
const OBJECT_LITERAL_RETURN = `
return {} as Foo
`;

ruleTester.run('consistent-type-assertions', rule, {
valid: [
Expand Down Expand Up @@ -89,6 +92,16 @@ ruleTester.run('consistent-type-assertions', rule, {
},
],
}),
...batchedSingleLineTests({
code: OBJECT_LITERAL_RETURN,
options: [
{
assertionStyle: 'as',
objectLiteralTypeAssertions: 'never',
allowAsReturn: true,
},
],
}),
...batchedSingleLineTests({
code: OBJECT_LITERAL_ARGUMENT_ANGLE_BRACKET_CASTS,
options: [
Expand Down Expand Up @@ -328,5 +341,21 @@ ruleTester.run('consistent-type-assertions', rule, {
},
],
}),
...batchedSingleLineTests({
code: OBJECT_LITERAL_RETURN,
options: [
{
assertionStyle: 'as',
objectLiteralTypeAssertions: 'never',
allowAsReturn: false,
},
],
errors: [
{
messageId: 'unexpectedObjectTypeAssertion',
line: 2,
},
],
}),
],
});