Re: syntax files: how to prevent embedded syntax from leaking out of a region?

"extend" clearly has the highest priority, so it cannot be overridden. But that's not the problem by itself. The real trouble is a misuse of it. It looks like every person out there starts playing with syntaxes by adding "keepend" and "extend" almost everywhere. While "extend" should only be used for those very special elements that essentially "violate normal rules", like escape sequences or such.

In other words, every inner syntax region is already "extend" by default, so an outer region _may_ put "keepend" to it if needed. But the inner region _under exceptional circumstances_ still may overpower it all with "extend". Maybe, we could add yet another override specially for syntax-include but, imo, that could lead to even more confusion. Instead, we should  better clean up existing syntax files from that garbage.

So, in my opinion, the whole issue is a consequence of having many poorly written syntax files. Main distribution included.

Kind regards,

Matvey

чт, 5 окт. 2023 г., 00:09 Edward McGuire <metaed@gmail.com>:

On Wednesday, October 4, 2023 at 1:55:55 PM UTC-5 Christian Brabandt wrote:
> Either nobody knows the answer or nobody understood the problem.

Thank you Christian, I'm glad to know it got out there anyway.

So maybe it will help for me to restate the problem, maybe not.

This has to do with syntax highlighting when a file written in one language has embedded in it a code block written in a different language.

The Vim distribution includes two great practical examples of how to do this.

Both examples highlight the code inside the block using different syntax rules than the code outside the block.

One is in help document "syntax.txt" under the tag "sh-embed".

This shows how to extend the sh syntax so that embedded awk code is highlighted using awk syntax.

The other is syntax file "ant.vim", which has a powerful technique to support multiple languages embedded in Ant syntax and highlight each language using the correct syntax file.

The problem I'm having is that sometimes code past the end of the block gets highlighted using the syntax rules for the code inside the block.

Here is an excerpt from the syntax I developed.

The excerpt highlights most of the buffer using the preinstalled "tex.vim".

Then, within any embedded code block introduced by a <<blockname>>= code block introducer, and terminated by an @ or another <<blockname>>= code block introducer, the embedded code block is highlighted by the preinstalled "make.vim".

syntax include @SyntaxTeX syntax/tex.vim

unlet b:current_syntax

syntax region Normal start=/\v%^/ end=/\v%$/ contains=@SyntaxTeX

syntax match nowebCodeChunkDeclarationMake "\v^[<][<][mM]akefile(|\s.*)[>][>][=]\s*$"

\ skipnl

\ containedin=@SyntaxTeX

\ nextgroup=nowebCodeChunkBodyMake

highlight link nowebCodeChunkDeclarationMake PreProc

syntax include @SyntaxMake syntax/make.vim

unlet b:current_syntax

syntax region nowebCodeChunkBodyMake

\ keepend

\ start="\v.*"

\ end="\v^([@]($| ))|([<][<].*[>][>][=][ \t]*$)"me=s-1

\ contained

\ contains=@SyntaxMake

The key bit is the "keepend" keyword on the embedded code block.

It is there to force the block terminator to also terminate any contained item.

It should stop the embedded language from reading past the block terminator.

But the embedded language syntax can override this using "extend".

That can cause the embedded language syntax highlighting to continue past the end of the code block delimiter.

And the problem seems to be that some of the preinstalled syntaxes do use "extend".

The question is how to prevent the preinstalled syntaxes from ever highlighting past the end of the delimiter.

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