Error thrown on nth-child with ExperimentalSpreadSyntax

[aduth]

Minimal reproduceable example:

https://astexplorer.net/#/gist/e0fb7d08090a532c3cdce571593671b2/622c0d4fed220a6b8d6655f0f746916aeb8bfb60

The :nth-child selector throws an error if object spread syntax (type of ExperimentalSpreadSyntax) is encountered.

Stack trace:

> eslint .

Cannot read property 'length' of undefined
TypeError: Cannot read property 'length' of undefined
    at nthChild (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/esquery/esquery.js:256:34)
    at matches (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/esquery/esquery.js:158:25)
    at Function.matches (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/esquery/esquery.js:103:25)
    at NodeEventGenerator.applySelector (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/util/node-event-generator.js:250:21)
    at NodeEventGenerator.applySelectors (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/util/node-event-generator.js:278:22)
    at NodeEventGenerator.enterNode (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/util/node-event-generator.js:294:14)
    at CodePathAnalyzer.enterNode (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/code-path-analysis/code-path-analyzer.js:608:23)
    at Traverser.enter [as _enter] (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/linter.js:1006:32)
    at Traverser._traverse (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/util/traverser.js:132:14)
    at Traverser._traverse (/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/node_modules/eslint/lib/util/traverser.js:147:30)

Throwing line:

esquery/esquery.js

Line 204 in 1853a6f

for (i = 0, l = keys.length; i < l; ++i) {

Real-world use-case:

I am trying to create a no-restricted-syntax ESLint rule for forbidding all but ArrayExpression as the second argument of Lodash methods which accept path argument:

CallExpression[callee.name=/^(invokeMap|get|has|hasIn|invoke|result|set|setWith|unset|update|updateWith)$/] > :not(ArrayExpression):nth-child(2)

This works in isolated usage:

https://astexplorer.net/#/gist/e0fb7d08090a532c3cdce571593671b2/b70d4572529d872e27f8c3df62c4ce0be43dba88

...but with above error, fails with the object spread syntax.

[michaelficarra]

The version of estraverse we use does not support ExperimentalSpreadSyntax nodes.

[brettz9]

@michaelficarra , what do you think of providing a method to have the user build an esquery instance with their own traverser and/or VisitorKeys baked in? (There was #105 , but maybe exposing a method would be clearer?)

The current default export could be made to rely on it, but if you were in favor of the idea, it wouldn't need to be a breaking change unless:

1. You wanted to change to named exports
2. You wanted to change to avoid bundling any default traverser/VisitorKeys at all

In the case of this particular issue, however, if it is possible for @aduth to use espree, I note that ESLint's default parser now, espree, can handle this syntax (as can the current version of estraverse in esquery), albeit as SpreadElement instead of ExperimentalSpreadSyntax, and requiring parser options at least as high as {ecmaVersion: 2018}.

[brettz9]

I believe this can be closed now (if the user supplies their own custom keys).

[michaelficarra]

Fixed by #112.