It is becoming somewhat ubiquitous that commands have tab completion/bash completion, so users will expect the same of us. It will likely be commands with many options or arguments that benefit the most from this, like tlctl.
I had a look at different tools for providing shell completions in a declarative manner based on the argument parser object. • Ahead-of-time completion script generators • shtab <https://github.com/iterative/shtab> Completion script generation for argparse. Rather complex but noticeably faster than the alternatives below for obvious reasons. Supports both bash and zsh. Could possibly benefit from more granular phase separation complexity-wise. • Completion performed by the script itself • argcomplete <https://pypi.org/project/argcomplete/> Completion for argparse. Seems to be relatively widely used by individuals using many argparse but seldom bundled with other packages. Has good test coverage. Only first-class support for bash. Relatively slow but gives the programmer an easy time providing rich completions. • optcomplete <https://furius.ca/optcomplete/> Completion for optparse (the library currently used). Supports only Python 2 and does not look very promising at a first glance as the code is both unmaintained and littered with TODOs and has close to zero test coverage. Nonetheless it may have some good parts/ideas and is relatively compact. Supports both bash and zsh. So, the main trade-off that has to be made is between performance/low coupling and extendability/completion richness. The approach of spinning up a python interpreter for every completion also makes supporting multiple different shells easier. Also, note that we are running M.2 drives in our workstations and that the python start-up time on our machines are very fast compared to others when reasoning about the overhead of spinning up a python interpreter for every completion call.
