auto-detect --merge-install

[NikolasE]

Why is colcon not starting the build process if I omit the '--merge-install' flag after the first run? Can't we assume that the user intends to build in the same layout like last time?
So instead of forcing the user to type --merge-install every time (or use an alias or similar), couldn't colcon use the detected layout?

[dirk-thomas]

Can't we assume that the user intends to build in the same layout like last time?

I am not sure that would be a good heuristic. What if the user intended to do an isolated build and forgot that the workspace was previously built merged? If this choice would happen automatically there is no easy way to choose the opposite.

I think the concept of profiles as described in colcon/colcon-core#168 would be a better solution for this use case. The arguments from a previous invocation would be persistent and reapplied in future invocations.

[NikolasE]

Yes, that sounds like a good way to achieve what I was thinking about!