The docs say that the constraints file can be used more than once: https://pip-tools.readthedocs.io/en/latest/cli/pip-compile/

What is more, I think it is possible to do this today without this PR?

1. Add the constraints.txt files to data attribute.
2. Use $(location) in the args.

Am I missing something here?

The docs say that the constraints file can be used more than once: pip-tools.readthedocs.io/en/latest/cli/pip-compile

Fair point, we could support a list instead of a single file/label instead.

What is more, I think it is possible to do this today without this PR?

1. Add the constraints.txt files to data attribute.
2. Use $(location) in the args.

Am I missing something here?

The data attribute gets popped from the kwargs here,

But then it gets reincluded back in via

I think I am missing something crucial here. Just by reading the code, this looks like it should work. What is the minimum example that does not work?

I think I am missing something crucial here. Just by reading the code, this looks like it should work. What is the minimum example that does not work?

e10255e fails.

$ bazelisk build //:requirements.update
ERROR: rules_python/examples/pip_parse/BUILD.bazel:57:25: in args attribute of py_binary rule //:requirements.update: label '//:constraints.txt' in $(location) expression is not a declared
 prerequisite of this rule. Since this rule was created by the macro 'pip_compile', the error might have been caused by the macro implementation
ERROR: rules_python/examples/pip_parse/BUILD.bazel:57:25: Analysis of target '//:requirements.update' failed
ERROR: Analysis of target '//:requirements.update' failed; build aborted
INFO: Elapsed time: 0.175s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
ERROR: Build did NOT complete successfully

102a76a is the minimal change to get it working again. I'm fine with that patch instead if you don't want to support an explicit arg.

No, I think the extra attribute for constraints makes sense. The only remaining thing here then is to make it a list.