bug#57042: 28.1.91; c-mode autoindents cweb style lines

bug#57042: 28.1.91; c-mode autoindents cweb style lines

[Van Ly]

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Hello,

C Mode autoindents CWEB style lines undesirably.

Steps to reproduce
  . starting from 'emacs -Q'
  . open new file 'C-x f /dev/shm/explain.w'
  . enable mode for C 'M-x c-mode'
  . enter the C CWEB style source text below
  . Explanation}
      the last two lines autoindent but I expect them to be without
  . at line 6 below at # position c-set-offset reports 'cpp-macro'
  . at line 0 below at # position c-set-offset reports 'cpp-macro'

Expected result is for lines 6, F and 0 below to be without indent.

```
1 @** Convert 511 decimal to octal.
2 @d _x_number_x_ 511
3 @d _x_banner_x_ "What is the value of %d in octal?"
4 @c
5 #include <stdio.h>
6 #include "u.h"
7 int@/
8 main(void)@/
9 {
A   int n = _x_number_x_;
B   printf (_x_banner_x_, n);
C   printf ("%s! %d decimal is %o octal\n", "Right", n, n);
D }
E @ @(u.h@>=
F     @h
0     #include <stdlib.h>
```

-- 
vl

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In GNU Emacs 28.1.91 (build 1, aarch64-unknown-linux-gnu, GTK+ Version 3.24.24, cairo version 1.16.0)
 of 2022-08-08 built on charlie
Repository revision: 059ab47a0664012b4d8cf8cc36b7d8a28b80c614
Repository branch: main
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LC_ALL: en_AU.UTF-8
  value of $LANG: en_AU.UTF-8
  locale-coding-system: utf-8-unix

Major mode: C/*l

Minor modes in effect:
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  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
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  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
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Load-path shadows:
None found.

Features:
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move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 92389 4478)
 (symbols 48 9389 1)
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bug#57042: 28.1.91; c-mode autoindents cweb style lines

[Eli Zaretskii]

> Date: Sun, 7 Aug 2022 16:16:31 +0000 (UTC)
> From: Van Ly <van.ly@sdf.org>
> 
> C Mode autoindents CWEB style lines undesirably.
> 
> Steps to reproduce
>   . starting from 'emacs -Q'
>   . open new file 'C-x f /dev/shm/explain.w'
>   . enable mode for C 'M-x c-mode'
>   . enter the C CWEB style source text below
>   . Explanation}
>       the last two lines autoindent but I expect them to be without
>   . at line 6 below at # position c-set-offset reports 'cpp-macro'
>   . at line 0 below at # position c-set-offset reports 'cpp-macro'
> 
> Expected result is for lines 6, F and 0 below to be without indent.
> 
> ```
> 1 @** Convert 511 decimal to octal.
> 2 @d _x_number_x_ 511
> 3 @d _x_banner_x_ "What is the value of %d in octal?"
> 4 @c
> 5 #include <stdio.h>
> 6 #include "u.h"
> 7 int@/
> 8 main(void)@/
> 9 {
> A   int n = _x_number_x_;
> B   printf (_x_banner_x_, n);
> C   printf ("%s! %d decimal is %o octal\n", "Right", n, n);
> D }
> E @ @(u.h@>=
> F     @h
> 0     #include <stdlib.h>
> ```

Sorry, I don't understand: why do you expect C Mode to DTRT for CWEB
files?  The above is not valid C code, it's a different language that
needs a dedicated major mode.

bug#57042: 28.1.91; c-mode autoindents cweb style lines

[Van Ly]

On Sun, 7 Aug 2022, Eli Zaretskii wrote:

>
> Sorry, I don't understand: why do you expect C Mode to DTRT for CWEB
> files?  The above is not valid C code, it's a different language that
> needs a dedicated major mode.
>

Yes, there is a dedicated mode for cweb by dek.  I guess it is out of 
date in relation to modern Emacs.  I'm expecting c mode might have 
enough fuzzy heuristic to play well with cweb.  For example, skip the 
lines beginning with @ when autoindenting.  C code validity is a 
moving target.

-- 
vl

bug#57042: 28.1.91; c-mode autoindents cweb style lines

[Lars Ingebrigtsen]

Van Ly <van.ly@sdf.org> writes:

> Yes, there is a dedicated mode for cweb by dek.  I guess it is out of
> date in relation to modern Emacs.  I'm expecting c mode might have
> enough fuzzy heuristic to play well with cweb.  For example, skip the
> lines beginning with @ when autoindenting.  C code validity is a
> moving target.

c-mode doesn't support the cweb language, and won't do that, either.

It might make sense to add a package for doing that to ELPA, but I
haven't seen anybody request that either, so it seems like there's not
really much demand for it.

In any case, I don't think there's anything actionable here on the
Emacs side, so I'm closing this bug report.

bug#57042: 28.1.91; c-mode autoindents cweb style lines

[Van Ly]

On Sun, 7 Aug 2022, Lars Ingebrigtsen wrote:

>
> c-mode doesn't support the cweb language, and won't do that, either.
>
> It might make sense to add a package for doing that to ELPA, but I
> haven't seen anybody request that either, so it seems like there's not
> really much demand for it.
>

But I did when I discovered cweb is out there and working.  I posted a
bug report with  a link to the  cweb mode el file.   I guess ownership
and licensing bureaucratic complication make  it less available and to
keep  current.   Finding that  file  wasn't  easy.  Anyway,  cweb  has
intrinsic value  in as much  Emacs has.  Prog mode doesn't  indent the
second brace right at all which was why I tried the c mode next.

'C-c C-o' can tell c mode to override the autoindent to offset 0.

-- 
vl