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[RFC] Don't show "display"s twice in MI


If you run "gdb -i=mi2" and set a "display", then when "next"ing the
displays will be shown twice:

    ~"1: x = 23\n"
    ~"7\t  printf(\"%d\\n\", x);\n"
    ~"1: x = 23\n"
    *stopped,reason="end-stepping-range",frame={addr="0x0000000000400565",func="main",args=[],file="q.c",fullname="/tmp/q.c",line="7"},thread-id="1",stopped-threads="all",core="1"

The immediate cause of this is this code in mi_on_normal_stop_1:

      print_stop_event (mi_uiout);

      console_interp = interp_lookup (current_ui, INTERP_CONSOLE);
      if (should_print_stop_to_console (console_interp, tp))
	print_stop_event (mi->cli_uiout);

... which obviously prints the stop twice.

However, I think the first call to print_stop_event is intended just
to emit the MI *stopped notification, which explains why the source
line does not show up two times.

This patch fixes the bug by changing print_stop_event to only call
do_displays for non-MI-like ui-outs.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-03-12  Tom Tromey  <tromey@adacore.com>

	* infrun.c (print_stop_event): Don't call do_displays for MI-like
	ui-outs.

gdb/testsuite/ChangeLog
2019-03-12  Tom Tromey  <tromey@adacore.com>

	* gdb.mi/mi2-cli-display.c: New file.
	* gdb.mi/mi2-cli-display.exp: New file.
---
 gdb/ChangeLog                            |  5 ++
 gdb/infrun.c                             |  3 +-
 gdb/testsuite/ChangeLog                  |  5 ++
 gdb/testsuite/gdb.mi/mi2-cli-display.c   | 30 ++++++++++++
 gdb/testsuite/gdb.mi/mi2-cli-display.exp | 62 ++++++++++++++++++++++++
 5 files changed, 104 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.c
 create mode 100644 gdb/testsuite/gdb.mi/mi2-cli-display.exp

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 33e5d434b35..9261588db32 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -7867,7 +7867,8 @@ print_stop_event (struct ui_out *uiout)
     print_stop_location (&last);
 
     /* Display the auto-display expressions.  */
-    do_displays ();
+    if (!uiout->is_mi_like_p ())
+      do_displays ();
   }
 
   tp = inferior_thread ();
diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.c b/gdb/testsuite/gdb.mi/mi2-cli-display.c
new file mode 100644
index 00000000000..813fda47cfc
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi2-cli-display.c
@@ -0,0 +1,30 @@
+/* Copyright 2019 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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 do_tests (int x)
+{
+  ++x;
+  ++x;
+  ++x;
+  ++x;
+  return x;
+}
+
+int main (void)
+{
+  return do_tests (23);
+}
diff --git a/gdb/testsuite/gdb.mi/mi2-cli-display.exp b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
new file mode 100644
index 00000000000..b11306a51cd
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi2-cli-display.exp
@@ -0,0 +1,62 @@
+# Copyright 2019 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/>.
+
+# Ensure that CLI "display"s aren't double-emitted in MI mode.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi2"
+
+if {[mi_gdb_start]} {
+    continue
+}
+
+standard_testfile
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+    untested "failed to compile"
+    return -1
+}
+
+mi_delete_breakpoints
+mi_gdb_reinitialize_dir $srcdir/$subdir
+mi_gdb_load ${binfile}
+
+mi_runto do_tests
+
+mi_gdb_test "display x" \
+    "&\"display x\\\\n\"\r\n~\"1: x = 23\\\\n\"\r\n\\^done" \
+    "display x"
+
+mi_send_resuming_command "interpreter-exec console next" next
+
+# Now check for the display and the source line.  Note we don't check
+# the source line too closely, since it's not really important here.
+gdb_expect {
+    -re "~\"1: x = 24\\\\n\"\r\n~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
+	# This case is the bug: the display is shown twice.
+	fail "check display and source line"
+    }
+    -re "~\"\[0-9\]+.*\\\\n\"\r\n~\"1: x = 24\\\\n\"\r\n" {
+	pass "check display and source line"
+    }
+    -re ".*\r\n$mi_gdb_prompt$" {
+	fail "check display and source line"
+    }
+    timeout {
+	fail "check display and source line"
+    }
+}
+
+mi_expect_stop end-stepping-range {.*} {.*} {.*} {.*} {.*} "stop for next"
-- 
2.20.1


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