command: capture command now handles both types commands

Commands that output progress output and no return value
will have the progress output captured.

Commands that do not output progress output(tcl commands)
will return the tcl return value instead.

The advantage here is that it is no longer necessary to
consider which command one is capturing, it works for
either.

Example #1: capture progress output:

set foo [capture help]

Example #2: capture tcl return value

set foo [capture {set abc def}]

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

src/helper/command.c

@@ -84,14 +84,36 @@ static struct log_capture_state *command_log_capture_start(Jim_Interp *interp)
 	return state;
 }
 
-static void command_log_capture_finish(struct log_capture_state *state)
+/* Classic openocd commands provide progress output which we
+ * will capture and return as a Tcl return value.
+ *
+ * However, if a non-openocd command has been invoked, then it
+ * makes sense to return the tcl return value from that command.
+ *
+ * The tcl return value is empty for openocd commands that provide
+ * progress output.
+ *
+ * Therefore we set the tcl return value only if we actually
+ * captured output.
+ */
+static void command_log_capture_finish(struct log_capture_state *state) 
 {
 	if (NULL == state)
 		return;
 
 	log_remove_callback(tcl_output, state);
 
-	Jim_SetResult(state->interp, state->output);
+	int length;
+	Jim_GetString(state->output, &length);
+
+	if (length > 0)
+	{
+		Jim_SetResult(state->interp, state->output);
+	} else
+	{
+		/* No output captured, use tcl return value (which could
+		 * be empty too). */
+	}
 	Jim_DecrRefCount(state->interp, state->output);
 
 	free(state);