Bazel: pkg_tar fails to import gflags when using py3

[damienmg]

From https://github.com/bazelbuild/rules_docker/issues/169

On Linux Ubuntu 14.10 and bazel 0.5.4:

$ bazel build --force_python=py3 --python_path=/usr/bin/python3 :bazel-srcs
INFO: Analysed target //:bazel-srcs (0 packages loaded).
INFO: Found 1 target...
ERROR: /usr/local/google/home/dmarting/git/bazel/BUILD:63:1: error executing shell command: 'bazel-out/host/bin/tools/build_defs/pkg/build_tar --flagfile=bazel-out/local-py3-fastbuild/bin/bazel-srcs.args' failed (Exit 1)
Traceback (most recent call last):
  File "/usr/local/google/home/dmarting/.cache/bazel/_bazel_dmarting/4c68128ea7d752c9535d956d14249eea/bazel-sandbox/5414131446493874244/execroot/io_bazel/bazel-out/host/bin/tools/build_defs/pkg/build_tar.runfiles/io_bazel/tools/build_defs/pkg/build_tar.py", line 23, in <module>
    from third_party.py import gflags
  File "/usr/local/google/home/dmarting/.cache/bazel/_bazel_dmarting/4c68128ea7d752c9535d956d14249eea/bazel-sandbox/5414131446493874244/execroot/io_bazel/bazel-out/host/bin/tools/build_defs/pkg/build_tar.runfiles/io_bazel/third_party/py/gflags/__init__.py", line 1, in <module>
    from gflags import *
ImportError: No module named 'gflags'
Target //:bazel-srcs failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 1.721s, Critical Path: 0.83s
FAILED: Build did NOT complete successfully
$ bazel build :bazel-srcs
INFO: Analysed target //:bazel-srcs (0 packages loaded).
INFO: Found 1 target...
Target //:bazel-srcs up-to-date:
  bazel-bin/bazel-srcs.tar
INFO: Elapsed time: 0.867s, Critical Path: 0.03s
INFO: Build completed successfully, 2 total actions

[duggelz]

Looking at this change: https://github.com/bazelbuild/bazel/commit/d7f5c120417bc2d2344dfb285322355f225d9153#diff-9b37129659ed5796bc9a42ed36bb49e1

That updates gflags to 3.1.0. Comparing Bazel's copy to stock gflags 3.1.0, it appears to have manually edited all the import statements from a compatible form, to a form that can only work in Python 2. Presumably there was some other problem that motivated this?

CC @spxtr

[spxtr]

That's curious. On my arch box both bazel build --force_python=py3 --python_path=/usr/bin/python3 :bazel-srcs and bazel build :bazel-srcs complete successfully.

Comparing Bazel's copy to stock gflags 3.1.0, it appears to have manually edited all the import statements from a compatible form, to a form that can only work in Python 2. Presumably there was some other problem that motivated this?

How do you mean? IIRC I just copied the code directly.

[hwright]

Would it be worth using the newly-released abseil version of gflags directly, rather than importing a local copy: https://github.com/abseil/abseil-py/tree/master/absl/flags ?

[akirabaruah]

Comparing Bazel's copy to stock gflags 3.1.0, it appears to have manually edited all the import statements from a compatible form, to a form that can only work in Python 2. Presumably there was some other problem that motivated this?

How do you mean? IIRC I just copied the code directly.

Comparing upstream vs. bazel versions of gflags 3.1.0, it looks like from gflags was omitted from the import statements.

[gpshead]

The correct thing to do here is move off of gflags entirely, not carry your own copy of the ancient dead code at all. Use absl.flags from https://pypi.org/project/absl-py/.