bug#45160: 27.1; [C] wrong indent for knr-style arguments declaration

[Bruno <braoult@gmail.com>]

Within "emacs -Q" session, open the following C source file:

------------------------------ foo.c
int f(i, j, k)
int i;
int j;
int k;
{
return 1;
}

int g(i, j, k)
int i;
int j, k;
{
return 1;
}
------------------------------

Then, do "C-c ." (c-set-style) to "k&r", and "c-c c-o" (c-set-offset),
and set "knr-argdecl-intro" to "+".

We have now the following values in c-offsets-alist :
knr-argdecl-intro : +  (First line of a K&R C argument declaration)
knr-argdecl : 0        (Subsequent lines in a K&R C argument declaration)

re-indent foo.c. At this stage we expect the following indentation for
arguments declarations.

------------------------------ expected indentation
int f(i, j, k)
    int i;
    int j;
    int k;
{
    return 1;
}

int g(i, j, k)
    int i;
    int j, k;
{
    return 1;
}
------------------------------

But we get the following result (please note line 11).

------------------------------ emacs indentation
int f(i, j, k)
    int i;
    int j;
    int k;
{
    return 1;
}

int g(i, j, k)
    int i;
int j, k;
{
    return 1;
}
------------------------------

It should be noted that if we separate each argument on separate lines
(function f), indentation is correct.
It is incorrect if multiple variables are in same declaration (function
g).

Also, multiple variables on first arguments declaration line seems to
have correct indentation.

Regards,

Bruno.

In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.32)
 of 2020-10-29 built on lorien
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 20.04.1 LTS

Recent messages:
End of buffer [3 times]
Beginning of buffer [3 times]
Making completion list...
Beginning of buffer [3 times]
previous-line: Beginning of buffer
user-error: No further undo information
C-x C-g is undefined
previous-line: Beginning of buffer [10 times]
scroll-up-command: End of buffer
command-execute: Buffer is read-only: #<buffer *Bug Help*>
Quit
Configured features:
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MODULES THREADS PDUMPER GMP

Important settings:
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: en_IE.UTF-8
  value of $LC_NUMERIC: en_IE.UTF-8
  value of $LC_TIME: en_IE.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
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  mouse-wheel-mode: t
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  auto-composition-mode: t
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Load-path shadows:
None found.

Features:
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Memory information:
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