BUILD.bazel files cause package identification problems

[mjcarroll]

Environment

• OS Version: Ubuntu 20.04
• Source or binary build? Source Edifice build with colcon

Description

• Expected behavior: Build successfully completes
• Actual behavior: Colcon package identification fails because it sees both cmake and bazel

Steps to reproduce

1. Install colcon as well as the colcon-bazel extension: https://github.com/colcon/colcon-bazel
2. Attempt to build the ignition edifice workspace with colcon

Output

An example of colcon list shows that ign-math and ign-utils are both ignored because they match against both CMake and Bazel.

$ colcon list
[0.368s] WARNING:colcon.colcon_core.package_identification:No valid Build content
[0.371s] WARNING:colcon.colcon_core.package_identification:_identify(src/ign-math) has multiple matches and therefore is being ignored: bazel, cmake
[0.435s] WARNING:colcon.colcon_core.package_identification:No valid Build content
[0.438s] WARNING:colcon.colcon_core.package_identification:_identify(src/ign-utils) has multiple matches and therefore is being ignored: bazel, cmake
ignition-cmake2	src/ign-cmake	(cmake)
ignition-common4	src/ign-common	(cmake)
ignition-fuel_tools6	src/ign-fuel-tools	(cmake)
ignition-gazebo5	src/ign-gazebo	(cmake)
ignition-gui5	src/ign-gui	(cmake)
ignition-launch4	src/ign-launch	(cmake)
ignition-msgs7	src/ign-msgs	(cmake)
ignition-physics4	src/ign-physics	(cmake)
ignition-plugin1	src/ign-plugin	(cmake)
ignition-rendering5	src/ign-rendering	(cmake)
ignition-sensors5	src/ign-sensors	(cmake)
ignition-tools	src/ign-tools	(cmake)
ignition-transport10	src/ign-transport	(cmake)
sdformat11	src/sdformat	(cmake)

[mjcarroll]

As far as I can tell, there are a few ways to solve it.

1. If you aren't actively using bazel in colcon workspaces, remove the colcon-bazel extension
2. Alter the PRIORITY setting the colcon-bazel extension point to give CMake higher priority
   • Ref: https://github.com/colcon/colcon-core/blob/master/colcon_core/package_identification/__init__.py#L46
   • https://github.com/colcon/colcon-bazel/blob/master/colcon_bazel/package_identification/bazel.py#L26
3. Add a colcon.pkg to all ignition packages to make CMake explicit

[mjcarroll]

Another alternative is to use a colcon.meta file in the root of your colcon workspace.

{
  "paths": {
    "src/ign-utils": {
      "type": "cmake"
    },
    "src/ign-math": {
      "type": "cmake"
    },
    "src/ign-common": {
      "type": "cmake"
    },
  }
}

[chapulina]

I remember having this issue before:

gazebosim/gz-plugin#31 (review)

---

Option 1. sounds like a tough ask for all users and I'd like to avoid option 3 so we don't have one more file to maintain.

I didn't quite understand how a user can set the PRIORITY for option 2, is this something that can be set from ~/.colcon/defaults.yaml or something like that?

The colcon.meta option also sounds promising.

[luca-della-vedova]

I didn't quite understand how a user can set the PRIORITY for option 2, is this something that can be set from ~/.colcon/defaults.yaml or something like that?

The colcon.meta option also sounds promising.

+1 to both options, I also wonder if a different default priority for Bazel should be pushed upstream? While I understand that it would be an arbitrary choice to say what's higher priority between CMake and Bazel, it sounds like anything better than the current behavior (skipping the package altogether) would be better?

[mjcarroll]

I didn't quite understand how a user can set the PRIORITY for option 2, is this something that can be set from ~/.colcon/defaults.yaml or something like that?

Setting the priority wouldn't be a user choice. The bazel extension itself would have to be modified upstream so that it had a higher/lower priority than CMake so that one will always "win".

From my observations, colcon is used more widely with cmake/ros projects, so it seems like that would be the sane default, and users could use one of the approaches above to "force" bazel.

[mjcarroll]

I believe the colcon-bazel pull request will address this. You can install that version via pip:

 pip3 install -e git://github.com/colcon/colcon-bazel@reduce_priority#egg=colcon-bazel --upgrade --user

[mxgrey]

For future visitors to this issue, I needed to tweak @mjcarroll 's command to this:

pip3 install git+https://github.com/colcon/colcon-bazel@master#egg=colcon-bazel --upgrade --user

in particular I needed to use git+https: instead of only git:, otherwise GitHub hung up on me. The other changes in my command are just to (1) not leave an editable version of the package hanging around, and (2) use the master branch of colcon-bazel since the relevant PR has been merged.