Re: Fix pressing down in the TUI (Re: [RFC 8.3 0/3] Some style fixes)

[Eli Zaretskii <eliz@gnu.org>]

> Cc: gdb-patches@sourceware.org
> From: Pedro Alves <palves@redhat.com>
> Date: Fri, 15 Mar 2019 12:34:34 +0000
> 
> On 03/12/2019 04:44 PM, Eli Zaretskii wrote:
> > 1. The first patch fixes the problem noticed by Pedro: pressing DOWN
> > arrow in the command window doesn't scroll the source window.  This is
> > because we don't initialize the s->nlines field, and then
> > tui_vertical_source_scroll thinks we are off the chart.  This fixes
> > that:
> > 
> > --- gdb/source-cache.c~4	2019-03-10 08:34:47.422752400 +0200
> > +++ gdb/source-cache.c	2019-03-12 11:50:15.094147600 +0200
> > @@ -194,6 +194,12 @@ source_cache::get_source_lines (struct s
> >  	  std::ifstream input (fullname);
> >  	  if (input.is_open ())
> >  	    {
> > +	      if (s->line_charpos == 0)
> > +		{
> > +		  scoped_fd desc = open_source_file (s);
> > +		  if (desc.get () >= 0)
> > +		    find_source_lines (s, desc.get ());
> 
> I think this should return false if open_source_file fails?

How could it fail if input.is_open returns non-zero?  Are you thinking
about some race, whereby something deletes the file after the
constructor for 'input' returns?

> Otherwise this LGTM.  I see get_plain_source_lines has similar
> code, so my immediate thought was to move that to a helper function,
> but there's a difference that makes that unviable -- get_plain_source_lines
> always wants to open the source file first, while here we can avoid
> it unless line_charpos is 0.

Right.  Also, I originally hoped std::ifstream will have a way to get
at the underlying file descriptor, but no such luck, AFAICT.