Automatically prepend module to task logger name

Rather than having to edit every single task to specify a module
prefix, determing the module prefix automatically (usually "lsst")
and prepend it if the logger name is being determined
automatically.

Provide a flag to disable this such that specific Task implementations
can declare that the default name should be used on its own.

python/lsst/pipe/base/task.py

@@ -139,6 +139,10 @@ class Task:
     `~lsst.pipe.base.CmdLineTask` not Task.
     """
 
+    _add_module_logger_prefix = True
+    """Control whether the module prefix should be prepended to default
+    logger names."""
+
     def __init__(self, config=None, name=None, parentTask=None, log=None):
         self.metadata = dafBase.PropertyList()
         self.__parentTask: Optional[weakref.ReferenceType]
@@ -167,6 +171,17 @@ def __init__(self, config=None, name=None, parentTask=None, log=None):
             loggerName = self._fullName
             if log is not None and log.name:
                 loggerName = log.getChild(loggerName).name
+            elif self._add_module_logger_prefix:
+                # Prefix the logger name with the root module name.
+                # We want all Task loggers to have this prefix to make
+                # it easier to control them. This can be disabled by
+                # a Task setting the class property _add_module_logger_prefix
+                # to False -- in which case the logger name will not be
+                # modified.
+                module_name = self.__module__
+                module_root = module_name.split(".")[0] + "."
+                if not loggerName.startswith(module_root):
+                    loggerName = module_root + loggerName
 
         # Get a logger (that might be a subclass of logging.Logger).
         self.log = lsst.utils.logging.getLogger(loggerName)

tests/test_task.py

@@ -75,6 +75,7 @@ class AddMultConfig(pexConfig.Config):
 class AddMultTask(pipeBase.Task):
     ConfigClass = AddMultConfig
     _DefaultName = "addMult"
+    _add_module_logger_prefix = False
 
     """First add, then multiply"""
 
@@ -106,6 +107,11 @@ def failCtx(self):
             raise RuntimeError("failCtx intentional error")
 
 
+class AddMultTask2(AddMultTask):
+    """Subclass that gets an automatic logger prefix."""
+    _add_module_logger_prefix = True
+
+
 class AddTwiceTask(AddTask):
     """Variant of AddTask that adds twice the addend"""
 
@@ -172,6 +178,9 @@ def testLog(self):
         self.assertEqual(addMultTask.log.name, "tester.addMult")
         self.assertEqual(addMultTask.add.log.name, "tester.addMult.add")
 
+        addMultTask2 = AddMultTask2()
+        self.assertEqual(addMultTask2.log.name, "test_task.addMult")
+
     def testGetFullMetadata(self):
         """Test getFullMetadata()
         """