Add selective trace loggers

Add selective enabling of trace loggers as described in python-discord/bot#1529

2 files changed, 32 insertions, 2 deletions

diff --git a/bot/constants.py b/bot/constants.py
index 2313bfdb..ae6e02c1 100644
--- a/bot/constants.py
+++ b/bot/constants.py
@@ -138,6 +138,7 @@ class Client(NamedTuple):
     github_bot_repo = "https://github.com/python-discord/sir-lancebot"
     # Override seasonal locks: 1 (January) to 12 (December)
     month_override = int(environ["MONTH_OVERRIDE"]) if "MONTH_OVERRIDE" in environ else None
+    trace_loggers = environ.get("BOT_TRACE_LOGGERS")
 
 
 class Colours:
diff --git a/bot/log.py b/bot/log.py
index c8437505..5e0e909d 100644
--- a/bot/log.py
+++ b/bot/log.py
@@ -30,7 +30,6 @@ def setup() -> None:
     file_handler.setFormatter(log_format)
 
     root_logger = logging.getLogger()
-    root_logger.setLevel(logging.TRACE if Client.debug else logging.INFO)
     root_logger.addHandler(file_handler)
 
     if "COLOREDLOGS_LEVEL_STYLES" not in os.environ:
@@ -44,8 +43,9 @@ def setup() -> None:
     if "COLOREDLOGS_LOG_FORMAT" not in os.environ:
         coloredlogs.DEFAULT_LOG_FORMAT = format_string
 
-    coloredlogs.install(stream=sys.stdout)
+    coloredlogs.install(level=logging.TRACE, stream=sys.stdout)
 
+    root_logger.setLevel(logging.DEBUG if Client.debug else logging.INFO)
     # Silence irrelevant loggers
     logging.getLogger("discord").setLevel(logging.ERROR)
     logging.getLogger("websockets").setLevel(logging.ERROR)
@@ -53,6 +53,8 @@ def setup() -> None:
     logging.getLogger("matplotlib").setLevel(logging.ERROR)
     logging.getLogger("async_rediscache").setLevel(logging.WARNING)
 
+    _set_trace_loggers()
+
     root_logger.info("Logging initialization complete")
 
 
@@ -65,3 +67,30 @@ def _monkeypatch_trace(self: logging.Logger, msg: str, *args, **kwargs) -> None:
     """
     if self.isEnabledFor(logging.TRACE):
         self._log(logging.TRACE, msg, args, **kwargs)
+
+
+def _set_trace_loggers() -> None:
+    """
+    Set loggers to the trace level according to the value from the BOT_TRACE_LOGGERS env var.
+
+    When the env var is a list of logger names delimited by a comma,
+    each of the listed loggers will be set to the trace level.
+
+    If this list is prefixed with a "!", all of the loggers except the listed ones will be set to the trace level.
+
+    Otherwise if the env var begins with a "*",
+    the root logger is set to the trace level and other contents are ignored.
+    """
+    level_filter = Client.trace_loggers
+    if level_filter:
+        if level_filter.startswith("*"):
+            logging.getLogger().setLevel(logging.TRACE)
+
+        elif level_filter.startswith("!"):
+            logging.getLogger().setLevel(logging.TRACE)
+            for logger_name in level_filter.strip("!,").split(","):
+                logging.getLogger(logger_name).setLevel(logging.DEBUG)
+
+        else:
+            for logger_name in level_filter.strip(",").split(","):
+                logging.getLogger(logger_name).setLevel(logging.TRACE)