[RFC] Python's gdb.FRAME_UNWIND_NULL_ID is no longer used. What to do with it?

[Pedro Alves <palves@redhat.com>]

I'd assume scripts just check the result of Frame.unwind_stop_reason,
and compare it to gdb.FRAME_UNWIND_NO_REASON.  That at most, they'll
pass the result of Frame.unwind_stop_reason to
gdb.frame_stop_reason_string.  I'd prefer to just get rid of it, but
it may be best to keep this around for compatibility, in case a script
does refer to gdb.FRAME_UNWIND_NULL_ID directly.

In general, what's the policy for exposed constants like this in
Python?

gdb/
2013-11-28  Pedro Alves  <palves@redhat.com>

	* unwind_stop_reasons.def (UNWIND_NULL_ID): Update comment.

gdb/doc/
2013-11-28  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Frames In Python) <gdb.FRAME_UNWIND_NULL_ID>:
	Update comment.
---
 gdb/doc/gdb.texinfo         |  4 +++-
 gdb/unwind_stop_reasons.def | 10 +++-------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 004c376..ddb4b38 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -26556,7 +26556,9 @@ function to a string. The value can be one of:
 No particular reason (older frames should be available).
 
 @item gdb.FRAME_UNWIND_NULL_ID
-The previous frame's analyzer returns an invalid result.
+The previous frame's analyzer returns an invalid result.  This is no
+longer used by @value{GDBN}, and is kept only for backward
+compatibility.
 
 @item gdb.FRAME_UNWIND_OUTERMOST
 This frame is the outermost.
diff --git a/gdb/unwind_stop_reasons.def b/gdb/unwind_stop_reasons.def
index ca5a74a..2c3d341 100644
--- a/gdb/unwind_stop_reasons.def
+++ b/gdb/unwind_stop_reasons.def
@@ -31,13 +31,9 @@
    or we didn't fail.  */
 SET (UNWIND_NO_REASON, "no reason")
 
-/* The previous frame's analyzer returns an invalid result
-   from this_id.
-
-   FIXME drow/2006-08-16: This is how GDB used to indicate end of
-   stack.  We should migrate to a model where frames always have a
-   valid ID, and this becomes not just an error but an internal
-   error.  But that's a project for another day.  */
+/* This is no longer used anywhere, but it's kept because it's exposed
+   to Python.  This is how GDB used to indicate end of stack.  We've
+   now migrated to a model where frames always have a valid ID.  */
 SET (UNWIND_NULL_ID, "unwinder did not report frame ID")
 
 /* This frame is the outermost.  */
-- 
1.7.11.7