[gdb/tui] Fix shell command terminal settings

In bash I have the following terminal settings:
...
$ stty
speed 38400 baud; line = 0;
-brkint -imaxbel iutf8
...
and then in gdb using the shell command likewise:
...
(gdb) shell stty
speed 38400 baud; line = 0;
-brkint -imaxbel iutf8
(gdb)
...
and likewise using a shell session:
...
(gdb) shell
$ stty
speed 38400 baud; line = 0;
-brkint -imaxbel iutf8
$
...

But in TUI, we get different settings (removed runaway indentation for
readability):
...
(gdb) shell sttyspeed 38400 baud; line = 0;
min = 1; time = 0;
-brkint -icrnl -imaxbel iutf8
-onlcr
-icanon -echo

(gdb)
...
and consequently the shell is not really usable.  This is PR tui/18215.

The easiest way to fix this is to just temporarily leave TUI while in the shell,
leaving the output of the commands in CLI mode, but that's a bit confusing.

Fix this (as suggested in the PR) by restoring the initial terminal settings
while in the shell command, such that also in TUI we have:
...
(gdb) shell sttyspeed 38400 baud; line = 0;
-brkint -imaxbel iutf8

(gdb)
...

Tested on x86_64-linux.

Reported-By: Doug Evans <dje@google.com>
Approved-By: Tom Tromey <tom@tromey.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18215

gdb/cli/cli-cmds.c

@@ -51,6 +51,7 @@
 #include "cli/cli-cmds.h"
 #include "cli/cli-style.h"
 #include "cli/cli-utils.h"
+#include "terminal.h"
 
 #include "extension.h"
 #include "gdbsupport/pathstuff.h"
@@ -949,6 +950,9 @@ shell_escape (const char *arg, int from_tty)
 static void
 shell_command (const char *arg, int from_tty)
 {
+  scoped_gdb_ttystate save_restore_gdb_ttystate;
+  restore_initial_gdb_ttystate ();
+
   shell_escape (arg, from_tty);
 }
 

gdb/inflow.c

@@ -55,6 +55,20 @@ static void child_terminal_ours_1 (target_terminal_state);
 
 static struct serial *stdin_serial;
 
+/* See terminal.h.  */
+
+scoped_gdb_ttystate::scoped_gdb_ttystate ()
+{
+  m_ttystate = serial_get_tty_state (stdin_serial);
+}
+
+/* See terminal.h.  */
+
+scoped_gdb_ttystate::~scoped_gdb_ttystate ()
+{
+  serial_set_tty_state (stdin_serial, m_ttystate);
+}
+
 /* Terminal related info we need to keep track of.  Each inferior
    holds an instance of this structure --- we save it whenever the
    corresponding inferior stops, and restore it to the terminal when
@@ -163,6 +177,15 @@ set_initial_gdb_ttystate (void)
     }
 }
 
+/* See terminal.h.  */
+
+void
+restore_initial_gdb_ttystate ()
+{
+  if (initial_gdb_ttystate != nullptr)
+    serial_set_tty_state (stdin_serial, initial_gdb_ttystate);
+}
+
 /* Does GDB have a terminal (on stdin)?  */
 
 static int

gdb/terminal.h

@@ -19,6 +19,8 @@
 #ifndef GDB_TERMINAL_H
 #define GDB_TERMINAL_H
 
+#include "serial.h"
+
 struct inferior;
 
 extern void new_tty_prefork (std::string ttyname);
@@ -43,4 +45,17 @@ extern void gdb_save_tty_state (void);
    have had a chance to alter it.  */
 extern void set_initial_gdb_ttystate (void);
 
+/* Restore initial tty state.  */
+extern void restore_initial_gdb_ttystate (void);
+
+/* An RAII-based object that saves the tty state, and then restores it again
+   when this object is destroyed. */
+class scoped_gdb_ttystate
+{
+public:
+  scoped_gdb_ttystate ();
+  ~scoped_gdb_ttystate ();
+private:
+  serial_ttystate m_ttystate;
+};
 #endif /* GDB_TERMINAL_H */