Make shell completion instruction format Click 8.x and Click 7.x compatible?

[AndreasBackx]

First Check

• I added a very descriptive title here.
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Example Code

See below, unrelated.

Description

To request completions you have to use the variable name _{CLI_NAME}_COMPLETE to request a completion instruction, which is in the format {SHELL}_{INSTRUCTION} where instruction can be complete or source. Example:

eval "$(_FOO_BAR_COMPLETE=bash_source foo-bar)"

Click 8.0 changed this from {INSTRUCTION}_{SHELL} to the current {SHELL}_{INSTRUCTION}. #317 reverted this so it was backwards compatible, which is a good thing. The problem is that when we want to request an instruction and instruct what shell is used, we cannot write code to do this for a binary where we know it's Click but don't know if it's Typer/Click.

We have some tooling to make it easy to deploy CLIs in the company with autocomplete. Currently it adheres to the Click 8.0 spec and we have implemented a wrapper around clap_complete for Clap CLIs to have the same behaviour (somewhat). I was working on some Clap improvements here and part of this was potentially making Clap adhere to the Click 8.x spec for at least the source instruction. This hasn't been discussed for Clap however so this is not set in stone, definitely as I am not part of the "core maintainers".

This all means we can (and potentially future Clap versions might be able to) generate the completion files for Click 8.x and Clap CLIs. Though we cannot support Typer because it did the right thing and kept backwards-compatibility. I feel like it's moot trying to convince Click to change it now, hence why I'm making a post here. Could the implementation be made Click 8.x compatible in addition to Click 7.x compatibility? Then it will be possible for Click, Typer, and Clap CLIs to generate their autocompletion files in the same way.

Operating System

Linux, Windows, macOS, Other

Operating System Details

Unrelated.

Typer Version

0.4.0+

Python Version

Unrelated.

Additional Context

No response