Making next.js work under rules_js

[Zemnmez]

I'm having some trouble making next.js work under rules_js. The specific problem I am having trouble with is that next.js opens tsconfig.json in read-write mode, and Bazel (understandably) does not want the actions to an input to be in read-write mode. Thus, the node runtime crashes with an error.

My understanding is that tsconfig.json is a useful thing for next.js to have available in general, but more specifically, module resolution within my monorepo won't work without it because it uses absolute paths and baseUrl is needed for those. As a result, I'm attempting to pass the tsconfig.json in the project root to my next.js build action. It's important to note that next.js will not modify tsconfig.json within this run. It has no need to.

I've tried and considered a few approaches:

1. Using a jsconfig.json. This doesn't seem to work because next.js doesn't pick it up from the root without specifying something like tsconfigPath, and next.js does not seem to have a jsconfigPath equivalent.
2. Using an implicit jsconfig.json in the project dir, not the root dir. In this case, next.js doesn't appear to notice the jsconfig.json.
3. Allowing the tsconfig.json to be modifiable in the action by running next.js in a harness that writes tsconfig.json to a writable directory. I doubt this would work because tsconfig.json would necessarily not be in the $(BINDIR) tree, and so, baseUrl would not resolve correctly.
4. Patching the next.js NPM package. I've had trouble finding the exact call that opens tsconfig.json, and I theorise it might even be as deep as in webpack.

I'd like to hear if anyone has any thoughts as to a way forward here. I feel like it could be possible to have some kind of harness that allows "opening" read-only files as read-write, but fails only when an attempt at a write actually occurs.

The pull request I am working on is here: https://github.com/Zemnmez/monorepo/pull/2091/files

[Zemnmez]

I managed to get this to work by generating a jsconfig.json in the next project dir like this:

    # create a jsconfig allowing imports from root
    native.genrule(
        name = name + "_jsconfig",
        outs = ["jsconfig.json"],
        cmd_bash = """
            echo '{ "compilerOptions": { "baseUrl": \"""" + "/".join([ '..' for x in native.package_name().split("/") ]) + """\" }}' > $@
        """,
    )

For me, my inputs are all already compiled javascript, so this should work fine.