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consistent-type-assertions.ts
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consistent-type-assertions.ts
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import type { TSESTree } from '@typescript-eslint/utils';
import { AST_NODE_TYPES } from '@typescript-eslint/utils';
import * as util from '../util';
// intentionally mirroring the options
type MessageIds =
| 'as'
| 'angle-bracket'
| 'never'
| 'unexpectedObjectTypeAssertion';
type OptUnion =
| {
assertionStyle: 'as' | 'angle-bracket';
objectLiteralTypeAssertions?: 'allow' | 'allow-as-parameter' | 'never';
}
| {
assertionStyle: 'never';
};
type Options = [OptUnion];
export default util.createRule<Options, MessageIds>({
name: 'consistent-type-assertions',
meta: {
type: 'suggestion',
docs: {
description: 'Enforce consistent usage of type assertions',
recommended: 'strict',
},
messages: {
as: "Use 'as {{cast}}' instead of '<{{cast}}>'.",
'angle-bracket': "Use '<{{cast}}>' instead of 'as {{cast}}'.",
never: 'Do not use any type assertions.',
unexpectedObjectTypeAssertion: 'Always prefer const x: T = { ... }.',
},
schema: [
{
oneOf: [
{
type: 'object',
properties: {
assertionStyle: {
enum: ['never'],
},
},
additionalProperties: false,
required: ['assertionStyle'],
},
{
type: 'object',
properties: {
assertionStyle: {
enum: ['as', 'angle-bracket'],
},
objectLiteralTypeAssertions: {
enum: ['allow', 'allow-as-parameter', 'never'],
},
},
additionalProperties: false,
required: ['assertionStyle'],
},
],
},
],
},
defaultOptions: [
{
assertionStyle: 'as',
objectLiteralTypeAssertions: 'allow',
},
],
create(context, [options]) {
const sourceCode = context.getSourceCode();
function isConst(node: TSESTree.TypeNode): boolean {
if (node.type !== AST_NODE_TYPES.TSTypeReference) {
return false;
}
return (
node.typeName.type === AST_NODE_TYPES.Identifier &&
node.typeName.name === 'const'
);
}
function reportIncorrectAssertionType(
node: TSESTree.TSTypeAssertion | TSESTree.TSAsExpression,
): void {
const messageId = options.assertionStyle;
// If this node is `as const`, then don't report an error.
if (isConst(node.typeAnnotation) && messageId === 'never') {
return;
}
context.report({
node,
messageId,
data:
messageId !== 'never'
? { cast: sourceCode.getText(node.typeAnnotation) }
: {},
});
}
function checkType(node: TSESTree.TypeNode): boolean {
switch (node.type) {
case AST_NODE_TYPES.TSAnyKeyword:
case AST_NODE_TYPES.TSUnknownKeyword:
return false;
case AST_NODE_TYPES.TSTypeReference:
return (
// Ignore `as const` and `<const>`
!isConst(node) ||
// Allow qualified names which have dots between identifiers, `Foo.Bar`
node.typeName.type === AST_NODE_TYPES.TSQualifiedName
);
default:
return true;
}
}
function checkExpression(
node: TSESTree.TSTypeAssertion | TSESTree.TSAsExpression,
): void {
if (
options.assertionStyle === 'never' ||
options.objectLiteralTypeAssertions === 'allow' ||
node.expression.type !== AST_NODE_TYPES.ObjectExpression
) {
return;
}
if (
options.objectLiteralTypeAssertions === 'allow-as-parameter' &&
(node.parent.type === AST_NODE_TYPES.NewExpression ||
node.parent.type === AST_NODE_TYPES.CallExpression ||
node.parent.type === AST_NODE_TYPES.ThrowStatement ||
node.parent.type === AST_NODE_TYPES.AssignmentPattern ||
node.parent.type === AST_NODE_TYPES.JSXExpressionContainer)
) {
return;
}
if (
checkType(node.typeAnnotation) &&
node.expression.type === AST_NODE_TYPES.ObjectExpression
) {
context.report({
node,
messageId: 'unexpectedObjectTypeAssertion',
});
}
}
return {
TSTypeAssertion(node): void {
if (options.assertionStyle !== 'angle-bracket') {
reportIncorrectAssertionType(node);
return;
}
checkExpression(node);
},
TSAsExpression(node): void {
if (options.assertionStyle !== 'as') {
reportIncorrectAssertionType(node);
return;
}
checkExpression(node);
},
};
},
});