[RFC] diagnostics.c: For terminals, restrict messages to terminal width?

[Tobias Burnus]

This patch fixes a Fortran diagnostic "regression".

With the current common diagnostic, the width shown with caret 
diagnostic is determined by:

     case OPT_fmessage_length_:
       pp_set_line_maximum_length (dc->printer, value);
       diagnostic_set_caret_max_width (dc, value);

plus

  diagnostic_set_caret_max_width (diagnostic_context *context, int value)
  {
    /* One minus to account for the leading empty space.  */
    value = value ? value - 1
      : (isatty (fileno (pp_buffer (context->printer)->stream))
        ? getenv_columns () - 1: INT_MAX);

    if (value <= 0)
      value = INT_MAX;

    context->caret_max_width = value;
  }

where getenv_columns looks at the environment variable COLUMNS.

Note that -fmessage-length= applies to the error message (wraps) _and_ 
the caret diagnostic (truncates) while the COLUMNS variable _only_ 
applies to the caret diagnostic. (BTW: The documentation currently does 
not mention COLUMNS.)

On most terminals, which I tried, COLUMNS does not seem to be set. In 
Fortran, error.c's get_terminal_width has a similar check, but 
additionally it uses ioctl to determine the terminal width.

I think with caret diagnostics, it is useful not to exceed the terminal 
width as having several "empty" lines before the "^" does not really 
improve the readability. Thus, I would propose to additionally use 
ioctl. Which rises two questions: (a) Should the COLUMNS environment 
variable or ioctl have a higher priority? [Fortran ranks ioctl higher; 
in the patch, for backward compatibilty, I rank COLUMNS higher.] (b) 
Should ioctl be always used or only for Fortran?

Comments?

Tobias
-------------- next part --------------
A non-text attachment was scrubbed...
Name: diag.diff
Type: text/x-patch
Size: 1272 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/fortran/attachments/20141206/7ee4804d/attachment.bin>