[PATCH 2/8] Don't create empty literal pieces

[Tom Tromey <tom@tromey.com>]

I noticed that format_pieces can create an empty literal piece.
However, there's never a need for one, so this patch removes the
possibility.

gdb/ChangeLog
2019-09-27  Tom Tromey  <tom@tromey.com>

	* unittests/format_pieces-selftests.c: Update.  Add final format.
	* gdbsupport/format.c (format_pieces::format_pieces): Don't add
	empty literal pieces.
---
 gdb/ChangeLog                           |  6 ++++++
 gdb/gdbsupport/format.c                 | 16 ++++++++++------
 gdb/unittests/format_pieces-selftests.c |  6 ++++--
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/gdb/gdbsupport/format.c b/gdb/gdbsupport/format.c
index fb3421e62bf..a5a367015f1 100644
--- a/gdb/gdbsupport/format.c
+++ b/gdb/gdbsupport/format.c
@@ -129,7 +129,8 @@ format_pieces::format_pieces (const char **arg)
 	current_substring += f - 1 - prev_start;
 	*current_substring++ = '\0';
 
-	m_pieces.emplace_back (sub_start, literal_piece);
+	if (*sub_start != '\0')
+	  m_pieces.emplace_back (sub_start, literal_piece);
 
 	percent_loc = f - 1;
 
@@ -340,11 +341,14 @@ format_pieces::format_pieces (const char **arg)
 
   /* Record the remainder of the string.  */
 
-  sub_start = current_substring;
+  if (f > prev_start)
+    {
+      sub_start = current_substring;
 
-  strncpy (current_substring, prev_start, f - prev_start);
-  current_substring += f - prev_start;
-  *current_substring++ = '\0';
+      strncpy (current_substring, prev_start, f - prev_start);
+      current_substring += f - prev_start;
+      *current_substring++ = '\0';
 
-  m_pieces.emplace_back (sub_start, literal_piece);
+      m_pieces.emplace_back (sub_start, literal_piece);
+    }
 }
diff --git a/gdb/unittests/format_pieces-selftests.c b/gdb/unittests/format_pieces-selftests.c
index 7d31b3cb93f..862b2da0f48 100644
--- a/gdb/unittests/format_pieces-selftests.c
+++ b/gdb/unittests/format_pieces-selftests.c
@@ -48,13 +48,15 @@ test_escape_sequences ()
 static void
 test_format_specifier ()
 {
-  check ("Hello %d%llx%%d", /* ARI: %ll */
+  /* The format string here ends with a % sequence, to ensure we don't
+     see a trailing empty literal piece.  */
+  check ("Hello %d%llx%%d%d", /* ARI: %ll */
     {
       format_piece ("Hello ", literal_piece),
       format_piece ("%d", int_arg),
-      format_piece ("", literal_piece),
       format_piece ("%llx", long_long_arg), /* ARI: %ll */
       format_piece ("%%d", literal_piece),
+      format_piece ("%d", int_arg),
     });
 }
 
-- 
2.17.2