bug#62204: 30.0.50; Feature Request: treesit-major-mode-hook

[Aleksandar Dimitrov]

I'd like to propose a major mode hook that is called every time any 
treesit-based major mode is enabled.

My use case is this: I'd like to extend the expand-region.el package so that it 
can make use of treesit to set the region to any treesit node. This should work 
in all treesit-based major modes.

Currently, I've found two ways to accomplish loading my functionality for all 
ts-modes:

- enumerate them all and use their respective hooks
- advise something like `treesit-major-mode-setup` to execute my code

The first idea might miss a mode if Emacs decides to add one down the
line, or if the user defines her own ts-mode.

The second idea does not feel idiomatic, as this sort of functionality
is usually covered by hooks.

I'd imagine there are other use cases for minor modes and other
functionality that we'd like to provide to any ts-based mode, not just
particular ones.

The concrete use-case is exemplified here:
https://github.com/magnars/expand-region.el/pull/279/