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Re: Tree-sitter introduction documentation

From: Dmitry Gutov
Subject: Re: Tree-sitter introduction documentation
Date: Tue, 27 Dec 2022 16:11:22 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2

On 27/12/2022 15:38, Eli Zaretskii wrote:
Date: Tue, 27 Dec 2022 14:43:06 +0200
Cc: monnier@iro.umontreal.ca, theophilusx@gmail.com, emacs-devel@gnu.org
From: Dmitry Gutov <dgutov@yandex.ru>

WDYT about what we have in NEWS about this?

Those instructions seem to be written foremost with distro maintainers
in mind.

Or users who build and install Emacs by themselves.

Frankly, I don't see why we, the upstream project, need to worry about
anyone else.  It isn't our job.  That's what distros are there for.

Previously all one needed for a language support mode is to download and load an .el file. As we drift to the idea of using externally-maintained grammars, and the "native" modes become less useful (possibly deprecated in 5-10), it seems like it will become more of our responsibility to streamline.

Definitely better to have them than not, but I'd hate to present
them to the average user.

"Hate"?  That's a strong word.

Also a figure of speech.

The questions that the NEWS entries
answer were asked here and elsewhere several times, so presumably that
information has some non-trivial value.

Of course.

Do we expect all (most?) distros to compile all the popular grammars?

I honestly don't know.  On the one hand, there aren't many Emacs modes
which use tree-sitter, but OTOH they could start growing like
mushrooms once Emacs 29 hits the streets.  I do expect them to offer
the ones they consider useful/needed, for some value of that.  I
really don't see any significant difference in this regard between
grammar libraries and, say, librsvg.  Both are used in Emacs, and the
lack of either disables useful Emacs features.  So it's a no-brainer
for me.  But then I'm not a distro maintainer, and never have been.

On the flip side, the third-party modes can provide their own download-compile-install instructions, which will make it easier to end users.

The barrier to creating such a mode, though, is now higher.

That would still leave out the users of the less popular languages whose
grammars were not included. Or grammars which saw updates since the
distro-distributed version (so it's useful to install the newer version).

What's the solution?  All the "solutions" I saw until now require a
working and well-configured C/C++ compiler (sometimes both C and C++),
linker, and C/C++ runtimes.  A user who has them already installed can
easily build a grammar library with two simple commands.  A user who
doesn't have a C/C++ development environment will not find those
"solutions" useful at all.  And asking us to distribute binaries for
half a dozen popular systems is IMNSHO unreasonable.

I think it's common enough for a user to have build tools installed, but not know well enough how to set up a C project. Think junior-middle developers in a number of languages which are not C.

Or just first grade students.

I wouldn't worry too much about the maintenance burden (keeping the list
of urls up-to-date?), especially since we could refer to such lists by
other projects.

I cannot disagree more.  Look at this from my POV: once the list
becomes even semi-official, people will expect it to be of the same
high quality as all the rest of Emacs, and they _will_ complain and
report inaccuracies.  It's a nuisance, especially for such a "hot"
feature set.

They will report inaccuracies, which will be helpful to fixing them. That is certainly a workload, but still small compared to the current flow of bug reports, I think. Or the many hours one would spend fixing a font- or redisplay-related problem.

Anyway, my point was not to put this burden on you specifically. If you might recall, I've always advocated toward "smaller core with many plugins" as a model of Emacs development.

And which "other projects"? who can track those and know which ones
have the most accurate, up-to-date, and comprehensive list?  I'm a bit
interested in this (and have several dozens of grammar libraries built
locally), and I discover another project with a useful list of
grammars almost every day.  These things are highly dynamic: I see
some of the grammars get updates every couple of days.  Some languages
have more than one grammar library maintained by different people --
who will figure out which one is better for us and keep that
information up-to-date?

The Neovim repo will likely be a good resource for this in the near future. This file in particular: https://github.com/nvim-treesitter/nvim-treesitter/blob/f2b1d727e6ad46238baa84c4d1f968a297e415ab/lua/nvim-treesitter/parsers.lua

But it brings me to another concern, showcased by this commit: https://github.com/nvim-treesitter/nvim-treesitter/commit/0cb637ca9f4389172933e5aba36387ab8430b6fb

The AST for one version of a grammar might be incompatible enough with a newer one, making the TS queries, font-lock and indentation rules obsolete or at least slightly broken. nvim-treesitter works around this by locking the repository version of a grammar corresponding to the current language support code.

How much this will be a problem in practice for us? I'm not sure. Perhaps most popular grammars have had enough time to mature by now.

I think ELPA is a better place for this feature, though. Because we
always want the user to get the latest version of the recipes.

That solves only part of the problem.  (And not an important part: our
Git repository is public, so people can track it and download updates
for files as easily as they track ELPA.)

One is not exactly like the other from an end user's POV.

The hard part -- keeping the
information accurate and up-to-date -- still needs a motivated
volunteer.  And we hardly have resources to work on our code and docs,
let alone help people install external software.

(Of course, if such a motivated volunteer steps forward, he or she
will be most welcome.)

My guess is we have a few people here already who might be interested.

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