Bug 1226554 - [mozlog] add a ProxyLogger concept. r=jgraham

--HG--
extra : commitid : Ez3CFCMZVYb
extra : rebase_source : f2515b3bf0fc813a3f10613fb8d1bc94878a6e60

testing/mozbase/docs/mozlog.rst

@@ -210,6 +210,33 @@ StructuredLogger Objects
 .. autoclass:: StructuredLogFileLike
   :members:
 
+ProxyLogger Objects
+-------------------
+
+Since :func:`mozlog.structuredlog.get_default_logger` return None when
+the default logger is not initialized, it is not possible to directly
+use it at the module level.
+
+With ProxyLogger, it is possible to write the following code: ::
+
+  from mozlog import get_proxy_logger
+
+  LOG = get_proxy_logger('component_name')
+
+
+  def my_function():
+      LOG.info('logging with a module level object')
+
+
+.. note::
+
+   mozlog still needs to be initialized before the first call occurs
+   to a ProxyLogger instance, for example with
+   :func:`mozlog.commandline.setup_logging`.
+
+.. automodule:: mozlog.proxy
+  :members: get_proxy_logger, ProxyLogger
+
 Handlers
 --------
 

testing/mozbase/mozlog/mozlog/__init__.py

@@ -19,6 +19,7 @@ from . import commandline
 from . import structuredlog
 from . import unstructured
 from .structuredlog import get_default_logger, set_default_logger
+from .proxy import get_proxy_logger
 
 # Backwards compatibility shim for consumers that use mozlog.structured
 structured = sys.modules[__name__]

testing/mozbase/mozlog/mozlog/proxy.py

@@ -0,0 +1,34 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from .structuredlog import get_default_logger
+
+
+class ProxyLogger(object):
+    """
+    A ProxyLogger behaves like a
+    :class:`mozlog.structuredlog.StructuredLogger`.
+
+    Each method and attribute access will be forwarded to the underlying
+    StructuredLogger.
+
+    RuntimeError will be raised when the default logger is not yet initialized.
+    """
+    def __init__(self, component=None):
+        self.logger = None
+        self._component = component
+
+    def __getattr__(self, name):
+        if self.logger is None:
+            self.logger = get_default_logger(component=self._component)
+            if self.logger is None:
+                raise RuntimeError("Default logger is not initialized!")
+        return getattr(self.logger, name)
+
+
+def get_proxy_logger(component=None):
+    """
+    Returns a :class:`ProxyLogger` for the given component.
+    """
+    return ProxyLogger(component)