gdb/mi: add --no-connection to MI -add-inferior command

Following on from the previous commit, where the -add-inferior command
now uses the same connection as the current inferior, this commit adds
a --no-connection option to -add-inferior.

This new option matches the existing option of the same name for the
CLI version of add-inferior; the new inferior is created with no
connection.

I've added a new 'connection' field to the MI output of -add-inferior,
which includes the connection number and short name.  I haven't
included the longer description field, this is the MI after all.  My
expectation would be that if the frontend wanted to display all the
connection details then this would be looked up from 'info
connection' (or the MI equivalent if/when such a command is added).

The existing -add-inferior tests are updated, as are the docs.

gdb/NEWS

@@ -158,6 +158,10 @@ info win
     connection of the current inferior, this restores the behaviour of
     GDB as it was prior to GDB 10.
 
+ ** The '-add-inferior' command now accepts a '--no-connection'
+    option, which causes the new inferior to start without a
+    connection.
+
 * New targets
 
 GNU/Linux/LoongArch    loongarch*-*-linux*

gdb/doc/gdb.texinfo

@@ -3310,6 +3310,7 @@ remove inferiors from the debugging session use the
 @w{@code{remove-inferiors}} command.
 
 @table @code
+@anchor{add_inferior_cli}
 @kindex add-inferior
 @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ] [-no-connection ]
 Adds @var{n} inferiors to be run using @var{executable} as the
@@ -37141,15 +37142,45 @@ popup menu, but is needless clutter on the command line, and
 @subheading Synopsis
 
 @smallexample
--add-inferior
+-add-inferior [ --no-connection ]
 @end smallexample
 
 Creates a new inferior (@pxref{Inferiors Connections and Programs}).  The created
 inferior is not associated with any executable.  Such association may
 be established with the @samp{-file-exec-and-symbols} command
-(@pxref{GDB/MI File Commands}).  The command response has a single
-field, @samp{inferior}, whose value is the identifier of the
-thread group corresponding to the new inferior.
+(@pxref{GDB/MI File Commands}).
+
+By default, the new inferior begins connected to the same target
+connection as the current inferior.  For example, if the current
+inferior was connected to @code{gdbserver} with @code{target remote},
+then the new inferior will be connected to the same @code{gdbserver}
+instance.  The @samp{--no-connection} option starts the new inferior
+with no connection yet.  You can then for example use the
+@code{-target-select remote} command to connect to some other
+@code{gdbserver} instance, use @code{-exec-run} to spawn a local
+program, etc.
+
+The command response always has a field, @var{inferior}, whose value
+is the identifier of the thread group corresponding to the new
+inferior.
+
+An additional section field, @var{connection}, is optional.  This
+field will only exist if the new inferior has a target connection.  If
+this field exists, then its value will be a tuple containing the
+following fields:
+
+@table @samp
+@item number
+The number of the connection used for the new inferior.
+
+@item name
+The name of the connection type used for the new inferior.
+@end table
+
+@subheading @value{GDBN} Command
+
+The corresponding @value{GDBN} command is @samp{add-inferior}
+(@pxref{add_inferior_cli,,@samp{add-inferior}}).
 
 @subheading Example
 

gdb/mi/mi-main.c

@@ -1703,18 +1703,53 @@ mi_cmd_list_target_features (const char *command, char **argv, int argc)
 void
 mi_cmd_add_inferior (const char *command, char **argv, int argc)
 {
-  struct inferior *inf;
+  bool no_connection = false;
 
-  if (argc != 0)
-    error (_("-add-inferior should be passed no arguments"));
+  /* Parse the command options.  */
+  enum opt
+    {
+      NO_CONNECTION_OPT,
+    };
+  static const struct mi_opt opts[] =
+    {
+	{"-no-connection", NO_CONNECTION_OPT, 0},
+	{NULL, 0, 0},
+    };
+
+  int oind = 0;
+  char *oarg;
+
+  while (1)
+    {
+      int opt = mi_getopt ("-add-inferior", argc, argv, opts, &oind, &oarg);
+
+      if (opt < 0)
+	break;
+      switch ((enum opt) opt)
+	{
+	case NO_CONNECTION_OPT:
+	  no_connection = true;
+	  break;
+	}
+    }
 
   scoped_restore_current_pspace_and_thread restore_pspace_thread;
 
-  inf = add_inferior_with_spaces ();
+  inferior *inf = add_inferior_with_spaces ();
 
-  switch_to_inferior_and_push_target (inf, false, current_inferior ());
+  switch_to_inferior_and_push_target (inf, no_connection,
+				      current_inferior ());
 
   current_uiout->field_fmt ("inferior", "i%d", inf->num);
+
+  process_stratum_target *proc_target = inf->process_target ();
+
+  if (proc_target != nullptr)
+    {
+      ui_out_emit_tuple tuple_emitter (current_uiout, "connection");
+      current_uiout->field_unsigned ("number", proc_target->connection_number);
+      current_uiout->field_string ("name", proc_target->shortname ());
+    }
 }
 
 void

gdb/testsuite/gdb.mi/interrupt-thread-group.exp

@@ -57,19 +57,9 @@ mi_send_resuming_command "exec-continue --thread-group i1" \
 set use_second_inferior [expr {![use_gdb_stub]}]
 
 if { $use_second_inferior } {
-    # The inferior created by the -add-inferior MI command does not inherit the
-    # target connection of the first inferior.  If debugging through an
-    # extended-remote connection, that means we can't run that second inferior
-    # on the remote connection.  Use the add-inferior CLI command as a stop-gap.
-    if { [mi_is_target_remote] } {
-	mi_gdb_test "add-inferior" \
-	    "\\^done" \
-	    "add inferior 2"
-    } else {
-	mi_gdb_test "-add-inferior" \
-	    "\\^done,inferior=\"i2\"" \
-	    "add inferior 2"
-    }
+    mi_gdb_test "-add-inferior" \
+	"\\^done,inferior=\"i2\",connection=\\{\[^\}\]+\\}" \
+	"add inferior 2"
     mi_gdb_test "-file-exec-and-symbols --thread-group i2 $::binfile" \
 	"\\^done" \
 	"set executable of inferior 2"

gdb/testsuite/gdb.mi/mi-add-inferior.exp

@@ -79,7 +79,7 @@ mi_gdb_test "-add-inferior" \
     [multi_line "=thread-group-added,id=\"\[^\"\]+\"" \
 	 "~\"\\\[New inferior 2\\\]\\\\n\"" \
 	 "\~\"Added inferior 2 on connection ${conn_pattern}\\\\n\"" \
-	 "\\^done,inferior=\"\[^\"\]+\"" ] \
+	 "\\^done,inferior=\"\[^\"\]+\",connection=\{number=\"$decimal\",name=\"\[^\"\]+\"\}" ] \
     "mi add inferior"
 
 # Now run 'info inferiors' again to check that the currently selected
@@ -120,3 +120,11 @@ gdb_test_multiple "info inferiors" \
 	    pass $gdb_test_name
 	}
     }
+
+# Add a third inferior, but this time, use --no-connection.
+mi_gdb_test "-add-inferior --no-connection" \
+    [multi_line "=thread-group-added,id=\"\[^\"\]+\"" \
+	 "~\"\\\[New inferior 3\\\]\\\\n\"" \
+	 "\~\"Added inferior 3\\\\n\"" \
+	 "\\^done,inferior=\"\[^\"\]+\"" ] \
+    "mi add inferior with no connection"