How do I see the commands executed during a colcon build?

Question

colcon build invokes cmake --build which invokes the build tool (e.g., make), which invokes the compiler -- along the way it becomes difficult to see how the compiler is being invoked.

The log files only include stdout or stderr. Increasing the verbosity of colcon itself does not increase the verbosity of cmake.

Answer 1

Per the Colcon how to documentation, to show all subcommand output immediately on the console:

colcon <verb> --event-handlers console_direct+

Secondly, you need to get verbose output from the build tool, in which case setting the environment variable VERBOSE=1 worked. So altogether my command was:

VERBOSE=1 colcon build --event-handlers console_direct+ ...args...