Suppress printing unnecessary info in silent mode // Resolve #3837

HISTORY.rst

@@ -13,6 +13,7 @@ PlatformIO Core 5
 
 * Fixed a "The command line is too long" issue with a linking process on Windows (`issue #3827 <https://github.com/platformio/platformio-core/issues/3827>`_)
 * Fixed an issue with `device monitor <https://docs.platformio.org/page/core/userguide/device/cmd_monitor.html>`__ when the "send_on_enter" filter didn't send EOL chars (`issue #3787 <https://github.com/platformio/platformio-core/issues/3787>`_)
+* Fixed an issue with silent mode when unwanted data is printed to stdout (`issue #3837 <https://github.com/platformio/platformio-core/issues/3837>`_)
 
 5.1.0 (2021-01-28)
 ~~~~~~~~~~~~~~~~~~

platformio/platform/_run.py

@@ -134,7 +134,9 @@ class PlatformRunMixin(object):
                 args,
                 stdout=proc.BuildAsyncPipe(
                     line_callback=self._on_stdout_line,
-                    data_callback=lambda data: _write_and_flush(sys.stdout, data),
+                    data_callback=lambda data: None
+                    if self.silent
+                    else _write_and_flush(sys.stdout, data),
                 ),
                 stderr=proc.BuildAsyncPipe(
                     line_callback=self._on_stderr_line,