[Bug]: `entry_point` is duplicated when also included in data

[allsey87]

For a complete MRE of this issue including a VS Code devcontainer see: https://github.com/allsey87/aspect_rules_js_mre

This issue arises when a custom rule generate a single Javascript file that needs to be tested. For example, assume in the following BUILD file that custom_rule with name output returns a DefaultInfo provider with a single file output.js.

load("@aspect_rules_js//js:defs.bzl", "js_test")
load("//:custom_rule.bzl", "custom_rule")

custom_rule(
    name = "output",
)

js_test(
    name = "validate",
    entry_point = "output.js",
    data = [":output"],
    timeout = "short",
)

If data is omitted, we get an error:

Copying file output.js failed: missing input file '//:output.js'

If data is provided, we get the error:

file 'output.js' is generated by these conflicting actions:
Label: //:output, //:validate

For now, the only workaround (that I know of) is to create a custom wrapper that launches output.js:

load("@aspect_rules_js//js:defs.bzl", "js_test")
load("@bazel_skylib//rules:write_file.bzl", "write_file")
load("//:custom_rule.bzl", "custom_rule")

custom_rule(
    name = "output",
)

write_file(
    name = "wrapper",
    out = "wrapper.js",
    content = [
        "require('./output.js')"
    ]
)

js_test(
    name = "validate",
    entry_point = "wrapper.js",
    data = [":output"],
    timeout = "short",
)

[jbedard]

@allsey87 did you find any other workarounds for this?

I've adapted your test into a basic unit test and reproduced the issue: #2662

It seems like the .is_source is returning true for some reason, despite the fact that output.js is clearly a generic file. I tested with bazel 7-9 and they all seem to think your generated file is a source so it does the copy_js_file_to_bin_action on it, despite the actions.write already writing to that same location. I'm not sure if that makes this a bazel bug? 🤔

When your :output target only outputs a single file it seems you can do entry_point = ":output" to workaround this, otherwise an extra wrapper file like you mentioned would be the other workaround.

[jbedard]

FYI @allsey87 one way to workaround this is for your custom_rule to use predeclared outputs and predeclare the fact that it outputs output.js. Then when you refer to output.js bazel knows it is not a source file.

I think the issue is when you simply have "output.js" passed as a string to a rule bazel doesn't (yet) know it is a generated file.

The other option might be changing custom_rule to only output a single file in the DefaultInfo and do entry_point = ":output", and the rest of the files can be returned from custom_rule via JsInfo.

[jbedard]

Standalone repro without any rulesets: https://github.com/jbedard/rjs-2190-repro