Redirect python logging in debug mode (#642)

This is handy for debugging what Glean and other low-level libraries
used by mozregression are doing.

gui/mozregui/main.py

@@ -4,6 +4,8 @@ from mozlog.structuredlog import StructuredLogger, set_default_logger
 from PySide2.QtCore import Qt
 from PySide2.QtWidgets import QApplication
 
+from mozregression.log import init_python_redirect_logger
+
 from .check_release import CheckRelease
 from .crash_reporter import CrashReporter
 from .global_prefs import set_default_prefs
@@ -13,7 +15,9 @@ from .mainwindow import MainWindow
 
 def main():
     logger = StructuredLogger("mozregression-gui")
+    init_python_redirect_logger(logger)
     set_default_logger(logger)
+
     # Create a Qt application
     log_model = LogModel()
     logger.add_handler(log_model)

mozregression/log.py

@@ -4,6 +4,7 @@ Logging and outputting configuration and utilities.
 
 from __future__ import absolute_import
 
+import logging
 import sys
 import time
 
@@ -22,6 +23,22 @@ def _format_seconds(total):
     return "%2d:%05.2f" % (minutes, seconds)
 
 
+def init_python_redirect_logger(logger):
+    """Create a pipe to the main log, at debug level
+
+    This is so we can see logs from third party libraries (like Glean)
+    """
+
+    class RedirectHandler(logging.StreamHandler):
+        def emit(self, record):
+            logger.debug("{}: {}".format(record.name, str(record.msg) % record.args))
+
+    rh = RedirectHandler()
+    rh.setLevel(logging.DEBUG)
+    logging.root.addHandler(rh)
+    logging.root.setLevel(logging.DEBUG)
+
+
 def init_logger(debug=True, allow_color=ALLOW_COLOR, output=None):
     """
     Initialize the mozlog logger. Must be called once before using logs.
@@ -56,6 +73,8 @@ def init_logger(debug=True, allow_color=ALLOW_COLOR, output=None):
     handler = LogLevelFilter(StreamHandler(output, format_log), "debug" if debug else "info")
     logger.add_handler(handler)
 
+    init_python_redirect_logger(logger)
+
     set_default_logger(logger)
     return logger