number_or_range_parser::get_number, don't treat "1 -" as a range

While adding -OPT options to "frame apply level", I noticed that:

 (gdb) frame apply level 0 -[TAB]

wasn't completing on the supported options.  This commit fixes it.
We'll get instead:

  (gdb) frame apply level 0 -
  -c           -past-entry  -past-main   -q           -s

I added the isspace check because this case:

  (gdb) frame apply level 0-

can't be an option.

Tests for this will be in a new gdb.base/options.exp file, in a
following patch.  It will exercise all of:

  (gdb) frame apply level 0-
  (gdb) frame apply level 0 -
  (gdb) frame apply level 0 --
  (gdb) frame apply level 0 -- -

gdb/ChangeLog:
2019-06-13  Pedro Alves  <palves@redhat.com>

	* cli/cli-utils.c (number_or_range_parser::get_number): Do not
	parse a range if "-" is at the end of the string.

1 files changed, 12 insertions, 4 deletions

diff --git a/gdb/cli/cli-utils.c b/gdb/cli/cli-utils.c
index a24fe92..23296ce 100644
--- a/gdb/cli/cli-utils.c
+++ b/gdb/cli/cli-utils.c
@@ -233,10 +233,18 @@ number_or_range_parser::get_number ()
       /* Default case: state->m_cur_tok is pointing either to a solo
 	 number, or to the first number of a range.  */
       m_last_retval = get_number_trailer (&m_cur_tok, '-');
-      /* If get_number_trailer has found a -, it might be the start
-	 of a command option.  So, do not parse a range if the - is
-	 followed by an alpha.  */
-      if (*m_cur_tok == '-' && !isalpha (*(m_cur_tok + 1)))
+      /* If get_number_trailer has found a '-' preceded by a space, it
+	 might be the start of a command option.  So, do not parse a
+	 range if the '-' is followed by an alpha or another '-'.  We
+	 might also be completing something like
+	 "frame apply level 0 -" and we prefer treating that "-" as an
+	 option rather than an incomplete range, so check for end of
+	 string as well.  */
+      if (m_cur_tok[0] == '-'
+	  && !(isspace (m_cur_tok[-1])
+	       && (isalpha (m_cur_tok[1])
+		   || m_cur_tok[1] == '-'
+		   || m_cur_tok[1] == '\0')))
 	{
 	  const char **temp;