gdb: add the 'set/show suppress-cli-notifications' command

GDB already has a flag to suppress printing notification events, such
as thread and inferior context switches, on the CLI.  This is used
internally when executing commands.  Make the flag available to the
user via a new command.  This is expected to be useful in scripts.

For instance, suppose that when Inferior 1 gets to a certain state,
you want to add and set up a new inferior using the commands below,
but you also want to have a reduced/clean output.

  define do-setup
    printf "Setting up Inferior 2...\n"
    add-inferior -exec a.out
    inferior 2
    break file.c:3
    run
    inferior 1
    printf "Done\n"
  end

Currently, GDB prints

  (gdb) do-setup
  Setting up Inferior 2...
  [New inferior 2]
  Added inferior 2 on connection 1 (native)
  [Switching to inferior 2 [<null>] (/tmp/a.out)]
  Breakpoint 2 at 0x1155: file file.c, line 3.

  Thread 2.1 "a.out" hit Breakpoint 2, main () at file.c:3
  3         return 0;
  [Switching to inferior 1 [process 7670] (/tmp/test)]
  [Switching to thread 1.1 (process 7670)]
  #0  main () at test.c:2
  2         int a = 1;
  Done

GDB's Python API make it possible to capture and return GDB's output,
but this does not work for all the streams.  In particular, CLI
notification events are not captured:

  (gdb) python gdb.execute("do-setup", False, True)
  [Switching to inferior 2 [<null>] (/tmp/a.out)]

  Thread 2.1 "a.out" hit Breakpoint 2, main () at file.c:3
  3         return 0;
  [Switching to inferior 1 [process 8263] (/tmp/test)]
  [Switching to thread 1.1 (process 8263)]
  #0  main () at test.c:2
  2         int a = 1;

You can use the new "set suppress-cli-notifications" command to
suppress the output:

  (gdb) set suppress-cli-notifications on
  (gdb) do-setup
  Setting up Inferior 2...
  [New inferior 2]
  Added inferior 2 on connection 1 (native)
  Breakpoint 2 at 0x1155: file file.c, line 3.
  Done

gdb/NEWS

@@ -81,6 +81,14 @@ maint show gnu-source-highlight enabled
   styling to a particular source file, then the Python Pygments
   library will be used instead.
 
+set suppress-cli-notifications (on|off)
+show suppress-cli-notifications
+  This controls whether printing the notifications is suppressed for CLI.
+  CLI notifications occur when you change the selected context
+  (i.e., the current inferior, thread and/or the frame), or when
+  the program being debugged stops (e.g., because of hitting a
+  breakpoint, completing source-stepping, an interrupt, etc.).
+
 * Changed commands
 
 maint packet

gdb/cli/cli-cmds.c

@@ -192,6 +192,11 @@ static const char *const script_ext_enums[] = {
 
 static const char *script_ext_mode = script_ext_soft;
 
+
+/* User-controllable flag to suppress event notification on CLI.  */
+
+static bool user_wants_cli_suppress_notification = false;
+
 /* Utility used everywhere when at least one argument is needed and
    none is supplied.  */
 
@@ -2136,6 +2141,28 @@ show_max_user_call_depth (struct ui_file *file, int from_tty,
 		    value);
 }
 
+/* Implement 'show suppress-cli-notifications'.  */
+
+static void
+show_suppress_cli_notifications (ui_file *file, int from_tty,
+				 cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Suppression of printing CLI notifications "
+			    "is %s.\n"), value);
+}
+
+/* Implement 'set suppress-cli-notifications'.  */
+
+static void
+set_suppress_cli_notifications (const char *args, int from_tty,
+				cmd_list_element *c)
+{
+  cli_suppress_notification.user_selected_context
+    = user_wants_cli_suppress_notification;
+  cli_suppress_notification.normal_stop
+    = user_wants_cli_suppress_notification;
+}
+
 /* Returns the cmd_list_element in SHOWLIST corresponding to the first
    argument of ARGV, which must contain one single value.
    Throws an error if no value provided, or value not correct.
@@ -2734,6 +2761,18 @@ Make \"wLapPeu\" an alias of 2 nested \"with\":\n\
 
   set_cmd_completer_handle_brkchars (c, alias_command_completer);
 
+  add_setshow_boolean_cmd ("suppress-cli-notifications", no_class,
+			   &user_wants_cli_suppress_notification,
+			   _("\
+Set whether printing notifications on CLI is suppressed."), _("\
+Show whether printing notifications on CLI is suppressed."), _("\
+When on, printing notifications (such as inferior/thread switch)\n\
+on CLI is suppressed."),
+			   set_suppress_cli_notifications,
+			   show_suppress_cli_notifications,
+			   &setlist,
+			   &showlist);
+
   const char *source_help_text = xstrprintf (_("\
 Read commands from a file named FILE.\n\
 \n\

gdb/doc/gdb.texinfo

@@ -27211,6 +27211,75 @@ inside a cygwin window.
 Displays whether the debugger is operating in interactive mode or not.
 @end table
 
+@table @code
+@kindex set suppress-cli-notifications
+@item set suppress-cli-notifications
+If @code{on}, command-line-interface (CLI) notifications that are
+printed by @value{GDBN} are suppressed.  If @code{off}, the
+notifications are printed as usual.  The default value is @code{off}.
+CLI notifications occur when you change the selected context or when
+the program being debugged stops, as detailed below.
+
+@table @emph
+@item User-selected context changes:
+When you change the selected context (i.e.@: the current inferior,
+thread and/or the frame), @value{GDBN} prints information about the
+new context.  For example, the default behavior is below:
+
+@smallexample
+(gdb) inferior 1
+[Switching to inferior 1 [process 634] (/tmp/test)]
+[Switching to thread 1 (process 634)]
+#0  main () at test.c:3
+3         return 0;
+(gdb)
+@end smallexample
+
+When the notifications are suppressed, the new context is not printed:
+
+@smallexample
+(gdb) set suppress-cli-notifications on
+(gdb) inferior 1
+(gdb)
+@end smallexample
+
+@item The program being debugged stops:
+When the program you are debugging stops (e.g.@: because of hitting a
+breakpoint, completing source-stepping, an interrupt, etc.),
+@value{GDBN} prints information about the stop event.  For example,
+below is a breakpoint hit:
+
+@smallexample
+(gdb) break test.c:3
+Breakpoint 2 at 0x555555555155: file test.c, line 3.
+(gdb) continue
+Continuing.
+
+Breakpoint 2, main () at test.c:3
+3         return 0;
+(gdb)
+@end smallexample
+
+When the notifications are suppressed, the output becomes:
+
+@smallexample
+(gdb) break test.c:3
+Breakpoint 2 at 0x555555555155: file test.c, line 3.
+(gdb) set suppress-cli-notifications on
+(gdb) continue
+Continuing.
+(gdb)
+@end smallexample
+
+Suppressing CLI notifications may be useful in scripts to obtain a
+reduced output from a list of commands.
+@end table
+
+@kindex show suppress-cli-notifications
+@item show suppress-cli-notifications
+Displays whether printing CLI notifications is suppressed or not.
+@end table
+
 @node Extending GDB
 @chapter Extending @value{GDBN}
 @cindex extending GDB

gdb/testsuite/gdb.base/cli-suppress-notification.c

@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020-2022 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 global = 0;
+
+int
+main ()
+{
+  global++;
+  global++;
+  return 0;
+}

gdb/testsuite/gdb.base/cli-suppress-notification.exp

@@ -0,0 +1,39 @@
+# Copyright 2020-2022 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/>.
+
+# Test the set/show suppress-cli-notifications command.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" ${binfile} ${srcfile}]} {
+    return
+}
+
+if {![runto_main]} {
+    return
+}
+
+gdb_test "inferior 1" ".*Switching to inferior 1 .* to thread 1 .*" \
+    "inferior switch is not suppressed"
+
+gdb_test_no_output "set suppress-cli-notifications on"
+gdb_test_no_output "inferior 1" "inferior switch is suppressed"
+gdb_test_no_output "next" "stepping is suppressed"
+
+# Now check that suppression can be turned back off.
+gdb_test_no_output "set suppress-cli-notifications off"
+gdb_test "inferior 1" ".*Switching to inferior 1 .* to thread 1 .*" \
+    "inferior switch is not suppressed again"
+gdb_test "next" "return 0;" "stepping is not suppressed"