Fix PR tui/21216: TUI line breaks regression

Commit d7e747318f4d04 ("Eliminate make_cleanup_ui_file_delete / make
ui_file a class hierarchy") regressed the TUI's command window.
Newlines miss doing a "carriage return", resulting in output like:

~~~~~~~~~~~~~~~~~~
(gdb) helpList of classes of commands:

                                      aliases -- Aliases of other commands
                                                                          breakpoints -- Making program stop at certain points
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Before the commit mentioned above, the default ui_file->to_write
implementation had a hack that would defer into the ui_file->to_fputs
method.  The TUI's ui_file did not implement the to_write method, so
all writes would end up going to the ncurses window via tui_file_fputs
-> tui_puts.

After the commit above, the hack is gone, but the TUI's ui_file still
does not implement the ui_file::write method.  Since tui_file inherits
from stdio_file, writing to a tui_file ends up doing fwrite on the
FILE stream the TUI is "associated" with, via stdio_file::write,
instead of writing to the ncurses window.

The fix is to have tui_file override the "write" method.

New test included.

gdb/ChangeLog:
2017-03-08  Pedro Alves  <palves@redhat.com>

	PR tui/21216
	* tui/tui-file.c (tui_file::write): New.
	* tui/tui-file.h (tui_file): Override "write".
	* tui/tui-io.c (do_tui_putc, update_start_line): New functions,
	factored out from ...
	(tui_puts): ... here.
	(tui_putc): Use them.
	(tui_write): New function.
	* tui/tui-io.h (tui_write): Declare.

gdb/testsuite/ChangeLog:
2017-03-08  Pedro Alves  <palves@redhat.com>

	PR tui/21216
	* gdb.tui/tui-nl-filtered-output.exp: New file.

2 files changed, 62 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index f986520..0654bef 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2017-03-08  Pedro Alves  <palves@redhat.com>
 
+	PR tui/21216
+	* gdb.tui/tui-nl-filtered-output.exp: New file.
+
+2017-03-08  Pedro Alves  <palves@redhat.com>
+
 	* gdb.base/completion.exp: Move TUI completion tests to ...
 	* gdb.tui/completion.exp: ... this new file.
 
diff --git a/gdb/testsuite/gdb.tui/tui-nl-filtered-output.exp b/gdb/testsuite/gdb.tui/tui-nl-filtered-output.exp
new file mode 100644
index 0000000..d1f56f2
--- /dev/null
+++ b/gdb/testsuite/gdb.tui/tui-nl-filtered-output.exp
@@ -0,0 +1,57 @@
+# Copyright 2017 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/>.
+
+# Regression test for PR tui/21216 - TUI line breaks regression.
+#
+# Tests that newlines in filtered output force a "carriage return" in
+# the TUI command window.  With a broken gdb, instead of:
+#
+#  (gdb) printf "hello\nworld\n"
+#  hello
+#  world
+#  (gdb)
+#
+# we'd get:
+#
+#  (gdb) printf "hello\nworld\n"hello
+#                                    world
+#
+#  (gdb)
+
+gdb_exit
+gdb_start
+
+if {[skip_tui_tests]} {
+    return
+}
+
+# Enable the TUI.
+
+set test "tui enable"
+gdb_test_multiple "tui enable" $test {
+    -re "$gdb_prompt $" {
+	pass $test
+    }
+}
+
+# Make sure filtering/pagination is enabled, but make the window high
+# enough that we don't paginate in practice.
+gdb_test_no_output "set pagination on"
+gdb_test_no_output "set height 2000"
+
+gdb_test \
+    {printf "hello\nworld\n"} \
+    "hello\r\nworld" \
+    "correct line breaks"