gdb/cli: Improve UX when using list with no args

When using "list" with no arguments, GDB will first print the lines
around where the inferior is stopped, then print the next N lines until
reaching the end of file, at which point it warns the user "Line X out
of range, file Y only has X-1 lines.".  This is usually desirable, but
if the user can no longer see the original line, they may have forgotten
the current line or that a list command was used at all, making GDB's
error message look cryptic. It was reported in bugzilla as PR cli/30497.

This commit improves the user experience by changing the behavior of
"list" slightly when a user passes no arguments.  It now prints that the
end of the file has been reached and recommends that the user use the
command "list ." instead.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30497
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 44db019..3a1902a 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -1246,10 +1246,19 @@ list_command (const char *arg, int from_tty)
 	  list_around_line (arg, cursal);
 	}
 
-      /* "l" or "l +" lists next ten lines.  */
-      else if (arg == NULL || arg[0] == '+')
-	print_source_lines (cursal.symtab,
-			    source_lines_range (cursal.line), 0);
+      /* "l" and "l +" lists the next few lines, unless we're listing past
+	 the end of the file.  */
+      else if (arg == nullptr || arg[0] == '+')
+	{
+	  if (last_symtab_line (cursal.symtab) >= cursal.line)
+	    print_source_lines (cursal.symtab,
+				source_lines_range (cursal.line), 0);
+	  else
+	    {
+	      error (_("End of the file was already reached, use \"list .\" to"
+		       " list the current location again"));
+	    }
+	}
 
       /* "l -" lists previous ten lines, the ones before the ten just
 	 listed.  */