js_binary + ESM + hermeticity

[paullewis]

Assuming something like this in a BUILD file:

load("@aspect_rules_ts//ts:defs.bzl", "ts_project")
load("@aspect_rules_js//js:defs.bzl", "js_binary")
load("@aspect_rules_swc//swc:defs.bzl", "swc_transpiler")
load("@bazel_skylib//lib:partial.bzl", "partial")

ts_project(
    name = "src",
    srcs = [
        "src.ts",
    ],
    declaration = True,
    transpiler = partial.make(
        swc_transpiler,
        source_maps = "true",
        swcrc = "//:swcrc_esm",
    ),
    tsconfig = "//:tsconfig",
    deps = [
        "//:node_modules/@types/node",
    ],
)

js_binary(
    name = "src_bin",
    entry_point = ":src.js",
)

And assuming that the transpilation of src.ts makes an ESM bundle in bazel-dist, running the js_binary fails because the generated src.js file is neither src.mjs, nor does Node know to run as "type": "module".

In other words, bazel run //src:src_bin will fail:

(node:92736) Warning: To load an ES module, set "type": "module" in the package.json or use the .mjs extension.

However, if in the source tree I update the package.json file to have "type": "module", the js_binary will now run.

I'm not sure if this is a bug or a question, but I'm surprised that a change to the package.json file in the source tree affects the js_binary. I assumed (perhaps incorrectly) that there would be a sandbox for the node process underpinning js_binary, and that it wouldn't have access to a package.json in the source tree.

Am I missing something?

[gregmagolan]

Thanks for the report @paullewis . EMS requires escape the sandbox right now. Its a known issue, #362, and seems like a tricky one to fix.

[paullewis]

Ah, I see. Happy to close this if it's a dupe... wdyt?

[gregmagolan]

Sounds good. It will be linked in the history of #362 as well.