Fix deletion of FinishBreakpoints

Currently, FinishBreakpoints are set at the return address of a frame based on
the `finish' command, and are meant to be temporary breakpoints. However, they
are not being cleaned up after use, as reported in PR python/18655. This was
happening because the disposition of the breakpoint was not being set
correctly.

This commit fixes this issue by correctly setting the disposition in the
post-stop hook of the breakpoint. It also adds a test to ensure this feature
isn't regressed in the future.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18655

gdb/python/py-finishbreakpoint.c

@@ -145,7 +145,7 @@ bpfinishpy_post_stop_hook (struct gdbpy_breakpoint_object *bp_obj)
     {
       /* Can't delete it here, but it will be removed at the next stop.  */
       disable_breakpoint (bp_obj->bp);
-      gdb_assert (bp_obj->bp->disposition == disp_del);
+      bp_obj->bp->disposition = disp_del_at_next_stop;
     }
   catch (const gdb_exception &except)
     {

gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.c

@@ -0,0 +1,31 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see  <http://www.gnu.org/licenses/>.  */
+
+static int
+subroutine (int a)
+{
+  return a;
+}
+
+int
+main (void)
+{
+  int i;
+  for (i = 0; i < 5; i++)
+    subroutine (i);
+  return 0;
+}

gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.exp

@@ -0,0 +1,41 @@
+# Copyright (C) 2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check that FinishBreakpoints are deleted after use.
+
+load_lib gdb-python.exp
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
+    return -1
+}
+
+# Skip all tests if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+if ![runto_main] then {
+    return 0
+}
+
+# For remote host testing
+set pyfile [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]
+
+gdb_test "python print(len(gdb.breakpoints()))" "1" "check default BP count"
+gdb_test "source $pyfile" ".*Python script imported.*" \
+    "import python scripts"
+gdb_test "python print(len(gdb.breakpoints()))" "2" "check modified BP count"
+gdb_test "continue" "Breakpoint.*at.*" "run until FinishBreakpoint stops"
+gdb_test "python print(len(gdb.breakpoints()))" "2" "check BP count"

gdb/testsuite/gdb.python/py-finish-breakpoint-deletion.py

@@ -0,0 +1,32 @@
+# Copyright (C) 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+class MyFinishBreakpoint(gdb.FinishBreakpoint):
+    def stop(self):
+        print("stopped at MyFinishBreakpoint")
+        return self.return_value == 4
+
+
+class MyBreakpoint(gdb.Breakpoint):
+    def stop(self):
+        print("stopped at MyBreakpoint")
+        MyFinishBreakpoint()
+        return False
+
+
+MyBreakpoint("subroutine", internal=True)
+
+print("Python script imported")