[committed] diagnostics: add line numbers to source (PR other/84889)

[Manuel López-Ibáñez]

On 17/08/18 17:50, Andreas Schwab wrote:
> On Aug 17 2018, Manuel López-Ibáñez <lopezibanez@gmail.com> wrote:
> 
>> However, I see that GCC trunk still counts tabs as 1-column, probably
>> because emacs counts tabs as one column when interpreting column numbers
>> in the output of GCC.
> 
> That is not true.  Emacs is using screen columns by default for almost
> 20 years now (see compilation-error-screen-columns).

Maybe I didn't properly explain what I mean. I mean that Emacs counts a tab as 
a "GCC" column, whatever number of visual columns the tab is configured to be 
in Emacs. The following code (with a tab before 'a'):

/* ñ    /* */
/* a    /* */
	a

With gcc -c test.c -Wcomment, it gives:

test.c:1:10: warning: "/*" within comment [-Wcomment]
  /* ñ    /* */
           ^
test.c:2:9: warning: "/*" within comment [-Wcomment]
  /* a    /* */
          ^
test.c:3:2: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ at end of input
   a
   ^

When the above appears in a compilation-mode buffer, I can click (or press 
enter) on each diagnostic and Emacs will jump exactly to what is pointed by the 
"^". That is, for Emacs, 3:2 does not mean line 3, *visual* column 2. In my 
Emacs, it jumps to column 8 (where the "a" is).

Changing the output to be 3:9 (if GCC starts interpreting tabs as 8 spaces as 
recommended by the GCS or to the value given by -ftabstop) will make Emacs jump 
to the wrong place.

This is independent of multi-byte characters. GCC is pointing to the wrong 
place when the line contains "ñ".

I hope the above is clearer,

Manuel.