Subject: bug#70435: 30.0.50; cc-mode: <> are sometimes not reconized as parentheses

From: Alan Mackenzie <[email-masked]>
Date: Sun, 28 Apr 2024 15:44:35 +0000

Hello, Géza.

On Wed, Apr 17, 2024 at 12:47:25 +0200, Herman wrote:

> This is a subtle bug.  In some cases, <> template delimiters are
> not recognized as delimiters, but punctuation characters.

> Repro:
> - put the yasnippet file (included below) into
> <emacs-config-dir>/snippets/c++-mode/something
> - install yasnippet
> - start emacs
> - M-x c++-mode
> - M-x yas-minor-mode
> - load snippets with "M-x yas-reload-all"
> - write "ig", then press TAB to "yas-expand" the snippet
> - move the cursor on the opening "<", and execute "M-x describe-char"
> - notice that it will say "syntax: . which means: punctuation"
> - if you edit the buffer (like add a space somewhere), and execute
> describe-char again, Emacs will say "syntax: > which means: open,
> matches >", so the syntax class becomes correct.

You've been a little less than fully explicit, but I think you're
executing these commands in the *scratch* buffer.  The first two lines,
which are commented out in emacs-lisp-mode, are no longer commented out
in C++ Mode.  There is a whole line of garbage after the last end of
statement marker, the (double) semicolon on line 2.

On using ig<TAB> to insert the snippet, it is hardly surprising that CC
Mode's syntactic analysis gets confused.  If you first comment out those
first two lines (put the region around them and do C-c C-c), then the
inserted snippet appears to get the correct syntax on its template
markers.

I don't think there's a bug here.  If you could show ig<TAB> producing
the effect when typed inside a syntactically correct context, things
might be different.  Can you reproduce the effect in correct C++ code?

> A possible explanation for this is that yasnippet edits the buffer in a
> way that cc-mode doesn't notices the edit, so it has no chance to put
> the correct syntax info on the inserted characters.

> This is the snippet file (a simple template declaration):

> --8<---------------cut here---------------start------------->8---
> # -*- mode: snippet -*-
> # name: something
> # key: ig
> # --
> template <${1:typename AAA}> struct Foo;
> --8<---------------cut here---------------end--------------->8---

> In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, cairo version
>  1.18.0) of 2024-04-12 built on okoska
> Repository revision: b83d0d07bb316cd851517897a9d688d639441f90
> Repository branch: my-modifications
> Windowing system distributor 'The X.Org Foundation', version 11.0.12101008
> System Description: Debian GNU/Linux trixie/sid

-- 
Alan Mackenzie (Nuremberg, Germany).