treesit: Theme treesit.el variables

[RangHo]

Theme treesit--install-language-grammar-out-dir-history, and treesit-extra-load-path.

• This directory contains tree-sitter grammar shared object artifacts (basically, ELF files).
• The installation function included in this package takes care of creating the directory.

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The treesit component introduced since Emacs 29 requires that you build grammar libraries for each language you want to parse. Unfortunately, the default hard-coded search path for said libraries is user-emacs-directory/tree-sitter, littering our .emacs.d once again.

This patch reconciles this by:

1. specifying an alternative load path that is within the var directory (treesit-extra-load-path),
2. providing a default install directory for the treesit-install-language-grammar interactive function (treesit--install-language-grammar-out-dir-history).

Oddities

Unlike specified in the README file, the directory is named tree-sitter, instead of treesit, since it contains shared object artifacts that technically can be used by the legacy tree-sitter integration as well.

Also, the variable treesit--install-language-grammar-out-dir-history is not yet present on Emacs 29.1.90, and the interactive function treesit-install-language-grammar always litters the Emacs directory. The relevant patch was already made in April in commit emacs-mirror/emacs@c146bd893dfbc8a4c92f9d1f33def8f29e7ece1f, though.

[tarsius]

Thanks!

"Merged". (Side-note:)

Unfortunately this pull-request asks for your master branch to be merged into ours. It is better to use a dedicated feature branch instead, as explained here. It is too late for this pull-request now, but the next time you open a pull-request (in any repository really), then please use a feature branch.

_{This is a canned response; it may not apply 100% in this case.}

[leungbk]

This change causes issues for Nix users; those of us who use Nix to install our tree-sitter grammars have our Emacs' treesit-extra-load-path updated by Nix (using add-to-list) to contain /nix/store/hash123-emacs-packages-deps/lib: https://github.com/nixos/nixpkgs/blob/6a19af3e00770531136d8f27e3a452a549224bf4/pkgs/build-support/emacs/wrapper.nix#L166-L168

When I start up my Emacs, since this commit tosses out the Nix-prescribed update to treesit-extra-load-path, Emacs does not know where to find my pre-installed grammars.

Consequently, I am now using this in my config:

(let ((old-val treesit-extra-load-path))
  (use-package no-littering
    :ensure t
    :demand t
    :config
    (setq treesit-extra-load-path old-val)))

Ideally, upstream Emacs would use some defcustom somewhere here instead of hard-coding: https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/treesit.el?h=ff1f82cbe3fa9aee354581f2798faaae7163ea44#n3424

[tarsius]

Reverting for now. I was on the fence about this. Will have to think about it more. Open to suggestions.

[RangHo]

This change causes issues for Nix users; those of us who use Nix to install our tree-sitter grammars have our Emacs' treesit-extra-load-path updated by Nix

Geez, I was unaware of this. I shouldn't have assumed that distros don't meddle with default configurations... Sorry about that.

Ideally, upstream Emacs would use some defcustom somewhere here instead of hard-coding

I agree. Fiddling with the history variable as the initial commit I made was a pretty bad, but the only solution as well...

Since treesit-extra-load-path is a list of search paths, would it be possible to use add-to-list instead of regular setq to register the alternative paths?

While this add-to-list-if-defined structure will deviate from the rest of the configurations using setq only, I guess this is pretty much the only solution versatile enough to reconcile for differences in default configs. Well, until upstream creates a new custom variable, that is.

[tarsius]

Let's wait until this has been improved upstream. (And by "wait", I mean "feel free to bring this up upstream". :grinning: )