bug#54128: 27.2; c-paragraph-* variables not sufficiently documented

[John Hagerman]

[Sent manually because sending from Emacs didn't work.]


Save this as file "comment.c" (*.c as C-mode is important):
---8<---
// \details
// I want the previous line to be untouched by c-fill-paragraph.
--->8---

Dribble file:
comment.c<return><escape>q<escape>:(setq c-paragraph-separate "$\\|// 
\\\\[a-z]+$")<return><escape>:(c-setup-paragraph-variables)<return><escape>q

Summary of actions:
+ Read comment.c; C-mode is entered.
+ Move down one line and do c-fill-paragraph: the two lines are merged
+ Undo to revert to original two lines
+ Set c-paragraph-separate and update the C-mode variables
+ Do c-fill-paragraph again; this time the two lines are not merged

There is nothing wrong with these actions!  The bug is only about the
c-paragraph-* variable documentation.

The Bug:
The documentation for c-paragraph-separate and c-paragraph-start should
describe the fact that they must begin with "$\\|" to work properly.

Details:
// Upon entering C-mode, the value of c-paragraph-separate is "$".
//
// \details
// I want the previous line to be untouched by c-fill-paragraph.
// With c-paragraph-separate being "$", that line will be included
// in a paragraph fill.  So: I want lines matching "^// \\\\[a-z]+$"
// to stand alone.  I will modify c-paragraph-separate to get this.
//
// As always, fill-paragraph regexps do not start with "^".  After a
// fair amount of work I found that custom c-paragraph-separate (and
// c-paragraph-start) must begin with "$\\|" to work properly.  So I
// do this:
// (setq c-paragraph-separate "$\\|// \\\\[a-z]+$")
// (c-setup-paragraph-variables)
//
// This bug report is about the fact that c-paragraph-separate and
// c-paragraph-start must begin with "$\\|".  Ideally that would be
// fixed.  But at the least this fact should be described in the
// variables' documentation.


In GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30, cairo 
version 1.15.12)
 of 2021-06-11 built on depbldcs73
Windowing system distributor 'TigerVNC', version 11.0.11400000
System Description: CentOS Linux 7 (Core)

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Configured using:
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