PR mi/18833 gdb.execute ("set param value", to_string=True) will crash gdb if using MI

gdb/ChangeLog:

	* cli/cli-logging.c (pop_output_files): Don't restore redirection
	if MI-like.
	* mi/mi-out.c: #include "vec.h".
	(ui_filep): New type.
	(DEV_VEC_P (ui_filep)): New type.
	(struct ui_out_data) <buffer, original_buffer>: Delete.
	(struct ui_out_data) <streams>: New member.
	(mi_ui_out_impl): Add data_destroy field.
	(mi_field_string, mi_field_fmt): Update.
	(mi_flush, mi_redirect, field_separator): Update.
	(mi_open, mi_close): Update.
	(mi_out_buffered, mi_out_rewind, mi_out_put): Update.
	(mi_out_data_ctor, mi_out_data_dtor): New functions.
	(mi_out_new): Call mi_out_data_ctor.

testsuite/gdb/ChangeLog:

	* lib/gdb.exp (skip_python_tests_prompt): Renamed from
	skip_python_tests.  New arg prompt_regexp.
	(skip_python_tests): New function.
	* lib/mi-support.exp (mi_skip_python_tests): New function.
	* gdb.python/py-mi-objfile-gdb.py: New file.
	* gdb.python/py-mi-objfile.c: New file.
	* gdb.python/py-mi-objfile.exp: New file.

gdb/testsuite/gdb.python/py-mi-objfile-gdb.py

@@ -0,0 +1,27 @@
+# Copyright (C) 2015 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/>.
+
+# This file is part of the GDB testsuite.
+
+import gdb
+
+# PR 18833
+# We want to have two levels of redirection while MI is current_uiout.
+# This will create one for to_string=True and then another for the
+# parameter change notification.
+gdb.execute("set width 101", to_string=True)
+# And finally a command that will use the original MI stream, which in a
+# buggy gdb will use just-freed data.
+gdb.execute("list")

gdb/testsuite/gdb.python/py-mi-objfile.c

@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2015 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/>.  */
+
+int
+main (void)
+{
+  return 0;
+}

gdb/testsuite/gdb.python/py-mi-objfile.exp

@@ -0,0 +1,57 @@
+# Copyright (C) 2008-2015 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/>.
+
+# This file is part of the GDB testsuite.  It tests exercises PR 18833.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi2"
+
+gdb_exit
+if [mi_gdb_start] {
+    continue
+}
+
+standard_testfile
+set pyfile ${testfile}-gdb.py
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested ${testfile}.exp
+    return -1
+}
+
+if { [mi_skip_python_tests] } { continue }
+
+# Make the -gdb.py script available to gdb, it is automagically loaded by gdb.
+# Care is taken to put it in the same directory as the binary so that
+# gdb will find it.
+set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${pyfile}]
+
+mi_delete_breakpoints
+mi_gdb_reinitialize_dir $srcdir/$subdir
+mi_gdb_test "set auto-load safe-path ${remote_python_file}" \
+    {.*\^done} \
+    "set safe-path"
+
+if [is_remote host] {
+    set filename ${testfile}
+    remote_download host ${binfile} ${filename}
+} else {
+    set filename ${binfile}
+}
+
+# PR 18833.  This will cause an unpatched gdb to crash.
+mi_gdb_test "-file-exec-and-symbols ${filename}" \
+    ".*\\^done,line=.*${srcfile}\"" \
+    "file-exec-and-symbols operation"