gdb: don't use the global thread-id in the saved breakpoints file

I noticed that breakpoint::print_recreate_thread was printing the
global thread-id.  This function is used to implement the 'save
breakpoints' command, and should be writing out suitable CLI commands
for recreating the current breakpoints.  The CLI does not use global
thread-ids, but instead uses the inferior specific thread-ids,
e.g. "2.1".

After some discussion on the mailing list it was suggested that the
most consistent solution would be for the saved breakpoints file to
always contain the inferior-qualified thread-id, so the file would
include "thread 1.1" instead of just "thread 1", even when there is
only a single inferior.

So, this commit adds print_full_thread_id, which is just like the
existing print_thread_id, only it always prints the inferior-qualified
thread-id.

I then update the existing print_thread_id to make use of this new
function, and finally, I update  breakpoint::print_recreate_thread to
also use this new function.

There's a multi-inferior test that confirms the saved breakpoints file
correctly includes the fully-qualified thread-id, and I've also
updated the single inferior test gdb.base/save-bp.exp to have it
validate that the saved breakpoints file includes the
inferior-qualified thread-id, even for this single inferior case.

1 files changed, 15 insertions, 4 deletions

diff --git a/gdb/thread.c b/gdb/thread.c
index e4d98ce..3d4cba3 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1431,14 +1431,25 @@ show_inferior_qualified_tids (void)
 const char *
 print_thread_id (struct thread_info *thr)
 {
+  if (show_inferior_qualified_tids ())
+    return print_full_thread_id (thr);
+
+  char *s = get_print_cell ();
+
   gdb_assert (thr != nullptr);
+  xsnprintf (s, PRINT_CELL_SIZE, "%d", thr->per_inf_num);
+  return s;
+}
 
+/* See gdbthread.h.  */
+
+const char *
+print_full_thread_id (struct thread_info *thr)
+{
   char *s = get_print_cell ();
 
-  if (show_inferior_qualified_tids ())
-    xsnprintf (s, PRINT_CELL_SIZE, "%d.%d", thr->inf->num, thr->per_inf_num);
-  else
-    xsnprintf (s, PRINT_CELL_SIZE, "%d", thr->per_inf_num);
+  gdb_assert (thr != nullptr);
+  xsnprintf (s, PRINT_CELL_SIZE, "%d.%d", thr->inf->num, thr->per_inf_num);
   return s;
 }