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Re: Why tree-sitter instead of Semantic? (was Re: CC Mode with font-lock

From: Lynn Winebarger
Subject: Re: Why tree-sitter instead of Semantic? (was Re: CC Mode with font-lock-maximum-decoration 2)
Date: Tue, 16 Aug 2022 06:42:23 -0400

On Sun, Aug 14, 2022 at 3:24 PM Eric Ludlam <ericludlam@gmail.com> wrote:
> On 8/9/22 10:14 PM, Po Lu wrote:
> > Lynn Winebarger <owinebar@gmail.com> writes:
> >
> >> I'm curious, though, as to why Semantic/CEDET seems to have been
> >> superceded by external solutions like tree-sitter or LSP-based
> >> (non-emacs) servers.  One of the draws of Emacs for me is the
> >> "batteries included" nature of it having Emacs Lisp built in.  Is
> >> there a downside to using Semantic as the basis for improving my
> >> derived mode that's non-obvious?
> >
> > I think Semantic lost intertia after the original author lost interest
> > in it (or left for unrelated reasons, I don't remember which.)
> I eventually stopped pushing on CEDET for a few reasons - but a big one
> was that I don't code professionally anymore, and trying to wrestle the
> legal paperwork from my company and merges between repositories
> necessitated by those restrictions was just too troublesome.

Unfortunately, I feel your pain.

> I was also frequently surprised by how hard it was to get CEDET to 'just
> work' well enough for everyone to use it as intended, and how often
> people just jumped over to simpler one-off external tools because the
> full suite way CEDET works was too heavy a lift.  That in turn resulted
> in not a lot of contributors to help support/improve those workflows.
> Tools like LSP also became good enough where there was no way I could
> keep up.  I had hoped to pull data from external tools like lsp into the
> framework CEDET used, but again the simpler one-off tools were too
> appealing to that audience.
> Overall, I think that is fine though - having many projects
> experimenting with different techniques, and having the best solution
> win is the benefit of free software.  Developing CEDET back when it was
> the only game it town was a good time with many good people helping, and
> I am glad to have been a part of that, and I'm glad CEDET is still
> useful in many cases.

I think there should be a substantive place for such a framework in Emacs, regardless of external tools that can be used to provide some of the analysis.  Even if a mode doesn't use the parser generated by a grammar, the grammar can also provide a description of the syntactic structure that can be used in separating fontification from syntactic analysis.  If I understand it correctly, Semantic provides support for that generic approach and tying the classification to the text through overlays  It should be straightforward for a major mode to create a set of faces that can be applied generically by font-lock based on those overlays instead of via regular expressions on the underlying text.
I've skimmed lsp-mode, but I can't tell how it attaches the analysis from the server to the text.
Just looking at tsc-core's GitHub page, I don't see a similar generic approach being provided.  I get the impression there is a lot of dependence on the individual language/mode as to how the information gets incorporated in the fontification.


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