[RFA] Fix PR python/17981

[Tom Tromey <tom@tromey.com>]

PR python/17981 notes that gdb.breakpoints() returns None when there
are no breakpoints; whereas an empty list or tuple would be more in
keeping with Python and the documentation.

This patch fixes the bug by changing the no-breakpoint return to make
an empty tuple.

It's arguable whether this should be changed.  On the one hand, it may
mean some script has to adapt.  On the other hand, it's clearly better
this way.

Built and regtested on x86-64 Fedora 23.

2016-05-18  Tom Tromey  <tom@tromey.com>

	PR python/17981:
	* python/py-breakpoint.c (gdbpy_breakpoints): Return a new tuple
	when there are no breakpoints.

2016-05-18  Tom Tromey  <tom@tromey.com>

	PR python/17981:
	* gdb.python/py-breakpoint.exp (test_bkpt_basic): Add test for
	no-breakpoint case.
---
 gdb/ChangeLog                              | 6 ++++++
 gdb/python/py-breakpoint.c                 | 4 ++--
 gdb/testsuite/ChangeLog                    | 6 ++++++
 gdb/testsuite/gdb.python/py-breakpoint.exp | 5 ++++-
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 92024b6..53b11c0 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2016-05-18  Tom Tromey  <tom@tromey.com>
 
+	PR python/17981:
+	* python/py-breakpoint.c (gdbpy_breakpoints): Return a new tuple
+	when there are no breakpoints.
+
+2016-05-18  Tom Tromey  <tom@tromey.com>
+
 	* rust-lang.c (rust_subscript): Initialize "high".
 
 2016-05-17  Simon Marchi  <simon.marchi@ericsson.com>
diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
index 611a41e..ed9cae6 100644
--- a/gdb/python/py-breakpoint.c
+++ b/gdb/python/py-breakpoint.c
@@ -746,13 +746,13 @@ gdbpy_breakpoints (PyObject *self, PyObject *args)
   PyObject *list, *tuple;
 
   if (bppy_live == 0)
-    Py_RETURN_NONE;
+    return PyTuple_New (0);
 
   list = PyList_New (0);
   if (!list)
     return NULL;
 
-  /* If iteratre_over_breakpoints returns non NULL it signals an error
+  /* If iterate_over_breakpoints returns non NULL it signals an error
      condition.  In that case abandon building the list and return
      NULL.  */
   if (iterate_over_breakpoints (build_bp_list, list) != NULL)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index a773c63..c09e858 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2016-05-18  Tom Tromey  <tom@tromey.com>
+
+	PR python/17981:
+	* gdb.python/py-breakpoint.exp (test_bkpt_basic): Add test for
+	no-breakpoint case.
+
 2016-05-18  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* gdb.mi/mi-threads-interrupt.c: New file.
diff --git a/gdb/testsuite/gdb.python/py-breakpoint.exp b/gdb/testsuite/gdb.python/py-breakpoint.exp
index d1d1b22..0116705 100644
--- a/gdb/testsuite/gdb.python/py-breakpoint.exp
+++ b/gdb/testsuite/gdb.python/py-breakpoint.exp
@@ -34,12 +34,15 @@ proc test_bkpt_basic { } {
 	# Start with a fresh gdb.
 	clean_restart ${testfile}
 
+	# We should start with no breakpoints.
+	gdb_test "python print gdb.breakpoints()" "\\(\\)"
+
 	if ![runto_main] then {
 	    fail "Cannot run to main."
 	    return 0
 	}
 
-	# Initially there should be one breakpoint: main.
+	# Now there should be one breakpoint: main.
 	gdb_py_test_silent_cmd "python blist = gdb.breakpoints()" \
 	    "Get Breakpoint List" 0
 	gdb_test "python print (blist\[0\])" \
-- 
2.5.5