document convenient way to lay out all files in bazel-out

[mrmeku]

🐞 bug report

Affected Rule

The issue is caused by the rule: ts_project

Is this a regression?

No

Description

Consider what happens when you try to bundle a index.js emited by ts_project.

index.js is placed in execroot/workspace/bazel-out/k8-fastbuild/bin/index.js and tries to do a relative import of a non-generated file something like ./styles.css (other common scenarios would be a local .js, or .json file)

styles.css is placed in execroot/workspace/styles.css

So the relative import fails since the bundler doesn't know how to resolve things living bazel-out vs not in bazel-out

In order to fix this sort of thing we'll either need to layout the directory structure differently or provide some documentation on ways to configure bundlers to resolve these imports.

A clear and concise description of the problem...

🔬 Minimal Reproduction

#1770

🔥 Exception or Error

ERROR in ./bazel-out/k8-fastbuild/bin/index.js
Module not found: Error: Can't resolve './styles.css' in '.../execroot/react_webpack/bazel-out/k8-fastbuild/bin'
 @ ./bazel-out/k8-fastbuild/bin/index.js 5:13-36

🌍 Your Environment

Output of bazel version:

  
Build label: 2.2.0
Build target: bazel-out/k8-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar
Build time: Tue Mar 3 09:26:12 2020 (1583227572)
Build timestamp: 1583227572
Build timestamp as int: 1583227572
  

Rules_nodejs version:

(Please check that you have matching versions between WORKSPACE file and @bazel/* npm packages.)

  
http_archive(
    name = "build_bazel_rules_nodejs",
    sha256 = "d0c4bb8b902c1658f42eb5563809c70a06e46015d64057d25560b0eb4bdc9007",
    urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/1.5.0/rules_nodejs-1.5.0.tar.gz"],
)
  

[alexeagle]

js_library has a built-in copy_to_bin action on InputArtifacts so you get relative imports together again. That's how @gregmagolan solved this in the linker PR.

[alexeagle]

certainly not a ts_project bug, it's doing the right thing with its inputs and outputs.
The question is how the user should express that they want other sources of the bundler to be copied to the output tree. You could manually add copy_to_bin rules for it, but maybe we should make the js_library rule part of the public API, as it now does this https://github.com/bazelbuild/rules_nodejs/blob/1.5.0/internal/js_library/js_library.bzl#L57-L63

[alexeagle]

I'm doing some work right now with cra/react-scripts and copy_to_bin works pretty well, just use it as a drop-in replacement for filegroup and you get a self-contained output directory

[alexeagle]

We should add a bit of docs somewhere for 2.0 to explain the current situation.
IF js_library becomes public API then it changes what we tell you to do...

[alexeagle]

js_library not going public in time for 2.0, so I think this should slip too.