Allow valid/invalid cases in RuleTester to contain a syntax tree instead of example code

The version of ESLint you are using. v7.30.0

The problem you want to solve. Background: I am maintaining an eslint plugin that tries to detect DOM-based XSS. This plugin is very specific to Mozilla and uses our own set of trades-off in terms of false positives and false negatives. We don’t claim perfect detection and there are some obvious gaps that one has to accept when dealing with a dynamically typed, multi-paradigm language. However, this plugin has gained adoption outside of Mozilla and other projects are using it as well (Microsoft Edge, Wire IM, Kibana, …)

Precise use-case: We have some logic that tries to be exhaustive in terms of Expressions we can analyze. In particular, it is complaining for expressions that are not within a list of allowed expressions. This helps maintain the security guarantees we provide in our plugin and acts as a forcing function to adopt new JavaScript Syntax in lock-step with the tooling that is used to check it (here’s an example for the nullish assignment operator). Currently, we can not write a test for this scenario, becaus we cannot write code containing a “FantasyExpression”. It would be really nice to test this behavior using the RuleTester by providing an ast instead of a code attribute.

Your take on the correct solution to problem. Instead of requiring a code sample in RuleTester only require it optionally and allow ast instead.

Are you willing to submit a pull request to implement this change? Yes

[mdjermanovic]

Glad it helped!

I’m using the parser directly, e.g.:

const ts = require("@typescript-eslint/parser");

const code = "foo";
const ast = ts.parse(code, {
    tokens: true,
    comment: true,
    range: true,
    loc: true
});

// then stringify, save to file, etc.

astexplorer.net should do the same, but you’ll need to enable the options that are not set by default (loc, comment, and tokens):

[nzakas]

I don’t think we are going to move forward with a change here, as there are better options available.