requirements_test always pass if pip-compile fails to resolve dependency

[reiyw]

🐞 bug report

Affected Rule

The issue is caused by the rule: compile_pip_requirements

Is this a regression?

No.

Description

compile_pip_requirements produces a test target for checking pip-compile. This test generates a lock file from given requirements_in, and fails if the content is different from the original requirements_txt. However, if pip-compile fails to resolve the dependency, the test passes regardless of the contents of requirements_txt.

The cause of this issue is in: https://github.com/bazelbuild/rules_python/blob/c6970fc44877dbbbce84d17845d9bc797aefe299/python/pip_install/pip_compile.py#L70-L89
pip-compile exits with code 2 when it fails to resolve the dependency. However, the error code is not checked, and here the contents of requirements_txt and requirements_out are identical (copied immediately before and not updated by pip-compile), so the test passes.

I'm ready to send a PR to fix this issue, if relevant.

🔬 Minimal Reproduction

Example Project

WORKSPACE

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

# HEAD commit as of 2021-06-01.
RULES_PYTHON_COMMIT = "c6970fc44877dbbbce84d17845d9bc797aefe299"
RULES_PYTHON_DIGEST = "c43edeb59c6cb009f23f8e5603ce8fa1ca25a9084aae54513c82acfff06c3aaa"

http_archive(
    name = "rules_python",
    urls = [
        "https://github.com/bazelbuild/rules_python/archive/" + RULES_PYTHON_COMMIT + ".tar.gz",
    ],
    sha256 = RULES_PYTHON_DIGEST,
    strip_prefix = "rules_python-" + RULES_PYTHON_COMMIT,
)

load("@rules_python//python:pip.bzl", "pip_parse")
pip_parse(
    name = "my_deps",
    requirements_lock = "//:requirements.txt",
)

load("@my_deps//:requirements.bzl", "install_deps")
install_deps()

BUILD

load("@rules_python//python/pip_install:requirements.bzl", "compile_pip_requirements")

compile_pip_requirements(
    name = "requirements",
    extra_args = [
        "--quiet",
    ],
)

requirements.in

grpcio==1.38.0
# tensorflow 2.5.0 requires grpcio~=1.34.0, which is incompatible
tensorflow==2.5.0

requirements.txt

foo

Command

$ bazel test //:requirements_test

🔥 Exception or Error

INFO: Analyzed target //:requirements_test (9 packages loaded, 228 targets configured).
INFO: Found 1 test target...
Target //:requirements_test up-to-date:
  bazel-bin/requirements_test
INFO: Elapsed time: 5.532s, Critical Path: 4.88s
INFO: 2 processes: 2 processwrapper-sandbox.
INFO: Build completed successfully, 2 total actions
//:requirements_test                                                     PASSED in 4.8s

INFO: Build completed successfully, 2 total actions

🌍 Your Environment

Operating System:

  
Debian GNU/Linux 10 (buster)
  

Output of bazel version:

  
4.1.0
  

Rules_python version:

  
c6970fc44877dbbbce84d17845d9bc797aefe299
  

Anything else relevant?