fix: correct regexp slash escapes

[JoshuaKGoldberg]

Fixes #68 in support of eslint/eslint#16555.

This solution is a kind of hacky workaround based on #68's comments. It "encodes" all backslash-escaped forward slashes ('\\' + '/') with a backslash and an equivalent unicode character ('\\' + '\\x2F').

I think it would be much better to work within the PEG grammar in grammar.pegjs. Unfortunately, there is no backtracking or other nontrivial regular expression techniques in PEG.js. Expressions like d:[^\/]+ ("capture any number of characters other than /, under the name d") don't have a way I could find to, say, skip past a character like \.

& { predicate } and ! { predicate } with matchers like "/" d:.+ { ... } "/" or just "/" d:.+ { ... } also seemed promising. But then I couldn't figure out how to get it to match non-greedily: i.e. the full /foo\/bar/ instead of just /foo\/.

I don't often work with PEGs and am not confident I didn't miss some obvious technique. I hope someone who's more experienced in these matters will point something out that's more PEG-oriented. 🙂

[nzakas]

@michaelficarra can you take a look at this?

[michaelficarra]

@nzakas @JoshuaKGoldberg I've updated the PR to use the PEG to just parse the various components of the regexp. For now, the only parsing contexts are character classes, hex escapes, single-character escapes, and of course the top-level parsing context. Please review and also try it out to see if it works in your project. I also updated the tests to be more strict.

[michaelficarra]

Rebased.

[JoshuaKGoldberg]

✅ confirmed, that works for me! I posted the test case in eslint/eslint#16555 (comment):

For posterity, this is the basic test case I'm using in tests/lib/rules/no-restricted-syntax.js to test estools/esquery#149:

{
code: import values from 'some/path';,
options: ["ImportDeclaration[source.value=/^some\/path$/]"],
errors: [
{
messageId: "restrictedSyntax",
data: {
message:
"Using 'ImportDeclaration[source.value=/^some\/path$/]' is not allowed.",
},
},
],
}

Thanks for picking this up!

[michaelficarra]

@JoshuaKGoldberg published v1.7.0