/
no-non-null-asserted-optional-chain.ts
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/
no-non-null-asserted-optional-chain.ts
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import {
TSESTree,
TSESLint,
AST_NODE_TYPES,
} from '@typescript-eslint/experimental-utils';
import * as ts from 'typescript';
import * as semver from 'semver';
import * as util from '../util';
type MessageIds = 'noNonNullOptionalChain' | 'suggestRemovingNonNull';
const is3dot9 = semver.satisfies(
ts.version,
`>= 3.9.0 || >= 3.9.1-rc || >= 3.9.0-beta`,
{
includePrerelease: true,
},
);
export default util.createRule<[], MessageIds>({
name: 'no-non-null-asserted-optional-chain',
meta: {
type: 'problem',
docs: {
description:
'Disallows using a non-null assertion after an optional chain expression',
category: 'Possible Errors',
recommended: 'error',
suggestion: true,
},
messages: {
noNonNullOptionalChain:
'Optional chain expressions can return undefined by design - using a non-null assertion is unsafe and wrong.',
suggestRemovingNonNull: 'You should remove the non-null assertion.',
},
schema: [],
},
defaultOptions: [],
create(context) {
const sourceCode = context.getSourceCode();
function isValidFor3dot9(node: TSESTree.ChainExpression): boolean {
if (!is3dot9) {
return false;
}
// TS3.9 made a breaking change to how non-null works with optional chains.
// Pre-3.9, `x?.y!.z` means `(x?.y).z` - i.e. it essentially scrubbed the optionality from the chain
// Post-3.9, `x?.y!.z` means `x?.y!.z` - i.e. it just asserts that the property `y` is non-null, not the result of `x?.y`.
// This means that for > 3.9, x?.y!.z is valid!
// NOTE: these cases are still invalid:
// - x?.y.z!
// - (x?.y)!.z
const parent = util.nullThrows(
node.parent,
util.NullThrowsReasons.MissingParent,
);
const grandparent = util.nullThrows(
parent.parent,
util.NullThrowsReasons.MissingParent,
);
if (
grandparent.type !== AST_NODE_TYPES.MemberExpression &&
grandparent.type !== AST_NODE_TYPES.CallExpression
) {
return false;
}
const lastChildToken = util.nullThrows(
sourceCode.getLastToken(parent, util.isNotNonNullAssertionPunctuator),
util.NullThrowsReasons.MissingToken('last token', node.type),
);
if (util.isClosingParenToken(lastChildToken)) {
return false;
}
const tokenAfterNonNull = sourceCode.getTokenAfter(parent);
if (
tokenAfterNonNull != null &&
util.isClosingParenToken(tokenAfterNonNull)
) {
return false;
}
return true;
}
return {
'TSNonNullExpression > ChainExpression'(
node: TSESTree.ChainExpression,
): void {
if (isValidFor3dot9(node)) {
return;
}
// selector guarantees this assertion
const parent = node.parent as TSESTree.TSNonNullExpression;
context.report({
node,
messageId: 'noNonNullOptionalChain',
// use a suggestion instead of a fixer, because this can obviously break type checks
suggest: [
{
messageId: 'suggestRemovingNonNull',
fix(fixer): TSESLint.RuleFix {
return fixer.removeRange([
parent.range[1] - 1,
parent.range[1],
]);
},
},
],
});
},
};
},
});