Plugin `filter` RegEx doesn't support case-insensitive flag

[graysonlang]

The filter argument for the onResolve and onLoad plugin API doesn't appear to respect the RegExp case-insensitivity flag.

For example, the following will only match files ending in .cpp or .c but not .C or .CPP even though the i flag is specified at the end of the RegExp literal.

build.onResolve({ filter: /\.c(pp)?$/i }, (args) => { ... }

I also attempted to use the new RegExp('\.c(pp)?$', 'i') form but it didn't work either. 😔

[hyrious]

Yes, looking at the source it passes only the source of regexp from JS to Go. You may manually match all cases without the help of flags.

{ filter: /\.[Cc]([pP][pP])?$/ }

[graysonlang]

@hyrious Thanks for the link to the code that verifies what I'm seeing. I was mostly filing the issue to bring light to the lack of support. As you mentioned, this particular case could certainly be recomposed to handle all of the permutations as part of the pattern, though I intentionally picked a relatively simple case as an example. Sadly, expanding out my actual use case is a little bit messier. 😬

[evanw]

Thanks for bringing this to my attention. This is just an oversight. It hadn't occurred to me to test this, and it's never come up for me. Of course it's very reasonable that this should work.

The way esbuild handles this is by taking the JavaScript regexp source code and passing it to Go's regexp engine. Apparently Go handles flags differently from JavaScript. The JavaScript regular expression new RegExp('\.c(pp)?$', 'i') is equivalent to the Go regular expression regexp.MustCompile(`(?i)\.c(pp)?$`) (the i flag turns into a (?i) prefix). So I'll need to do that substitution in esbuild's API.

[graysonlang]

Thanks, Evan!