Build failure when CMAKE_PROJECT_NAME is not set

[cottsay]

There's some code in colcon_cmake which skips the package build when CMAKE_PROJECT_NAME is not set or could not be detected. When this case is triggered and the warning is printed because the cache is not readable, the code in colcon_ros tries to detect the availability of an install target, but fails to do so as this requires reading the cache as well. There appears to be an attempt to suppress this sort of error if the build invocation failed, but because of how colcon_cmake returned without an error, this logic fails and a backtrace is printed.

https://github.com/colcon/colcon-ros/blob/eb0b932cf7b1f3f5a720804e67f3c1a0f8995ca8/colcon_ros/task/cmake/build.py#L38-L44

[2.863s] colcon.colcon_cmake.task.cmake.build WARNING Could not build CMake package 'foobar' because the CMake cache has no 'CMAKE_PROJECT_NAME' variable
Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/colcon_core/executor/__init__.py", line 91, in __call__
    rc = await self.task(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/colcon_core/task/__init__.py", line 93, in __call__
    return await task_method(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/colcon_ros/task/ament_cmake/build.py", line 65, in build
    has_install_target = await has_target(args.build_base, 'install')
  File "/usr/lib/python3.9/site-packages/colcon_cmake/task/cmake/__init__.py", line 56, in has_target
    if 'Unix Makefiles' in generator:
TypeError: argument of type 'NoneType' is not iterable

The situation that led to this state was initially caused by user error, in which I had accidentally left the remnants of a prior invocation of CMake within the package sources. Removing these files resolved that specific issue.

[rsarrazin2]

Note that in my case, colcon's not finding the CMake cache variable CMAKE_PROJECT_NAME was due to its expecting CMakeCache.txt in the "wrong" folder. You can find the full description in my self-answered question How can I make colcon work with a plain preset-based CMake project with multiple presets in parallel?.

I add this comment here because that's where I landed searching for my problem.