[FR]: Add env argument to ts_project

[jamirvin]

What is the current behavior?

Currently there is no way to customize the environment variables that are set during the tsc execution.

Describe the feature

I am attempting to adopt ts_project on my very large Typescript codebase. In order to use tsc without running out of memory, we need to use the --max-old-space-size on the node process. ts_project does not currently provide a way to do this. I propose adding an env option to ts_project that gets passed though to the underlying action run.

Currently, our setup looks like this:

typescript_bin.tsc(
    name = "src_transpiled",
    args = [
        "-p",
        "tsconfig.json",
    ],
    chdir = package_name(),
    out_dirs = ["dist"],
    srcs = glob([
        "src/**/*"
    ]) + [
        "tsconfig.json",
    ],
    env = {
        "NODE_OPTIONS": "--max-old-space-size=10240",
    },
    visibility = ["//visibility:public"],
)

[alexeagle]

You can do this already by passing a tsc that has extra arguments baked into it.

rules_ts/examples/custom_compiler/BUILD.bazel

Line 31 in 04286dd

name = "tsc_with_more_heap",

It's not per-target, but of course you could make a tsc for one target to use. It would also be neat to accept a Partial as the value of tsc and then you could do it with less syntax.