[Bug]: Wrong launcher script detection, when a custom platform is used

[nosamad]

What happened?

When using a custom target platform for a different os than the execution platform, the wrong launcher script is selected.
E.g. selecting a windows target platform on a linux execution platform, selects the windows launcher script and vice-versa.

Version

Development (host) and target OS/architectures:

Output of bazel --version:
aspect 5.2.1

Version of the Aspect rules, or other relevant rules from your
WORKSPACE or MODULE.bazel file:
0eca3b9

Language(s) and/or frameworks involved:
C/C++ and JS, TypeScript

How to reproduce

Add a custom target platform for cross compile to a different OS than windows and try to build under windows.

Any other information?

https://github.com/nosamad/rules_js/tree/topic/fix_launcher_script_selection

[gregmagolan]

I believe Bazel is doing the right thing here and building the js_binary for the target platform. For build actions that use a js_binary, those should still be built for the execution platform via the cfg=exec transition, which would be the host if you're not using RBE. What is your use case?

[nosamad]

I believe Bazel is doing the right thing here and building the js_binary for the target platform. For build actions that use a js_binary, those should still be built for the execution platform via the cfg=exec transition, which would be the host if you're not using RBE. What is your use case?

My use case is, that i have a code-generator written in Javascript/ Typescript and a C/C++ Target Application, which depends on the generated sources and is compiled for the target platform.
When I set the target platform, to a non-windows target (e.g. GCC ARM Baremetal), the launcher script is wrong detected.
The host system is windows (not using RBE) and I get an error that the bash Script is not executable (Failed to start process).
The underlying toolchain (nodejs) is correctly selected for the execution platform - independent from the target platform.
I think the launcher script, should be selected according to the nodejs toolchain.

[gregmagolan]

Can you provide more details as to how the js_binary is being executed? Is it a custom rule? Are you calling bazel build or bazel run? Code snippets may be helpful.