Fix duplicate keyword argument error in configure_logging (#2381)

Allow traceback-related kwargs to override defaults by building a dict
with defaults first, then updating with user-provided values.

Fixes #2356

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: William Easton <strawgate@users.noreply.github.com>

src/fastmcp/utilities/logging.py

@@ -74,15 +74,19 @@ def configure_logging(
     import mcp
     import pydantic
 
-    traceback_handler = RichHandler(
-        console=Console(stderr=True),
-        show_path=False,
-        show_level=False,
-        rich_tracebacks=enable_rich_tracebacks,
-        tracebacks_max_frames=3,
-        tracebacks_suppress=[fastmcp, mcp, pydantic],
-        **rich_kwargs,
-    )
+    # Build traceback kwargs with defaults that can be overridden
+    traceback_kwargs = {
+        "console": Console(stderr=True),
+        "show_path": False,
+        "show_level": False,
+        "rich_tracebacks": enable_rich_tracebacks,
+        "tracebacks_max_frames": 3,
+        "tracebacks_suppress": [fastmcp, mcp, pydantic],
+    }
+    # Override defaults with user-provided values
+    traceback_kwargs.update(rich_kwargs)
+
+    traceback_handler = RichHandler(**traceback_kwargs)  # type: ignore[arg-type]
     traceback_handler.setFormatter(formatter)
 
     traceback_handler.addFilter(lambda record: record.exc_info is not None)

tests/utilities/test_logging.py

@@ -1,6 +1,6 @@
 import logging
 
-from fastmcp.utilities.logging import get_logger
+from fastmcp.utilities.logging import configure_logging, get_logger
 
 
 def test_logging_doesnt_affect_other_loggers(caplog):
@@ -28,3 +28,29 @@ def test_logging_doesnt_affect_other_loggers(caplog):
 
     finally:
         logging.getLogger("fastmcp").setLevel(original_level)
+
+
+def test_configure_logging_with_traceback_kwargs():
+    """Test that traceback-related kwargs can be passed without causing duplicate argument errors."""
+    # This should not raise TypeError about duplicate keyword arguments
+    configure_logging(enable_rich_tracebacks=True, tracebacks_max_frames=20)
+
+    # Verify the logger was configured
+    logger = logging.getLogger("fastmcp")
+    assert logger.handlers
+    assert len(logger.handlers) == 2  # One for normal logs, one for tracebacks
+
+
+def test_configure_logging_traceback_defaults_can_be_overridden():
+    """Test that default traceback settings can be overridden by kwargs."""
+    configure_logging(
+        enable_rich_tracebacks=True,
+        tracebacks_max_frames=20,
+        show_path=True,
+        show_level=True,
+    )
+
+    logger = logging.getLogger("fastmcp")
+    assert logger.handlers
+    # The traceback handler should have been created with custom values
+    # We can't directly inspect RichHandler internals easily, but we verified no error was raised