adjust deprecation handling

Author: strawgate

src/fastmcp/server/server.py

@@ -287,28 +287,22 @@ def _handle_lifespan_settings(
         session_lifespan: LifespanCallable | None = None,
         server_lifespan: LifespanCallable | None = None,
     ) -> tuple[LifespanCallable | None, LifespanCallable | None]:
-        if session_lifespan is not None:
-            if server_lifespan is not None:
-                raise ValueError(
-                    "Cannot specify both session_lifespan and server_lifespan."
-                )
-
+        if lifespan is not None:
             if fastmcp.settings.deprecation_warnings:
                 import warnings
 
                 warnings.warn(
-                    "The session_lifespan parameter is deprecated (as of 2.13.0). For the same behavior, "
-                    + "use the lifespan parameter instead.",
+                    "The lifespan parameter is deprecated (as of 2.13.0). For the same behavior, "
+                    + "use the session_lifespan parameter instead.",
                     DeprecationWarning,
                     stacklevel=2,
                 )
-            # Keep the provided session_lifespan. If it was not provided, fall back to lifespan below.
-        else:
-            session_lifespan = lifespan
 
-        if all([session_lifespan, server_lifespan]):
+        session_lifespan = lifespan or session_lifespan
+
+        if session_lifespan and server_lifespan:
             raise ValueError(
-                "Cannot specify both session_lifespan and server_lifespan."
+                "Cannot specify both session_lifespan (or lifespan) and server_lifespan."
             )
 
         return session_lifespan, server_lifespan

tests/server/test_mount.py

@@ -890,19 +890,6 @@ async def test_as_proxy_true(self):
         assert mcp._tool_manager._mounted_servers[0].server is not sub
         assert isinstance(mcp._tool_manager._mounted_servers[0].server, FastMCPProxy)
 
-    async def test_as_proxy_defaults_true_if_lifespan(self):
-        @asynccontextmanager
-        async def lifespan(mcp: FastMCP):
-            yield
-
-        mcp = FastMCP("Main")
-        sub = FastMCP("Sub", lifespan=lifespan)
-
-        mcp.mount(sub, "sub")
-
-        assert mcp._tool_manager._mounted_servers[0].server is not sub
-        assert isinstance(mcp._tool_manager._mounted_servers[0].server, FastMCPProxy)
-
     async def test_as_proxy_defaults_true_if_server_lifespan(self):
         """Test that as_proxy defaults to True when server_lifespan is provided."""
 
@@ -969,7 +956,7 @@ async def lifespan(mcp: FastMCP):
             yield
 
         mcp = FastMCP("Main")
-        sub = FastMCP("Sub", lifespan=lifespan)
+        sub = FastMCP("Sub", server_lifespan=lifespan)
 
         @sub.tool
         def hello():

tests/server/test_server_lifespan.py

@@ -98,17 +98,17 @@ async def session_lifespan(mcp: FastMCP) -> AsyncIterator[None]:
 
         with warnings.catch_warnings(record=True) as w:
             warnings.simplefilter("always")
-            _ = FastMCP(name="TestServer", session_lifespan=session_lifespan)
+            _ = FastMCP(name="TestServer", lifespan=session_lifespan)
 
             # Should have emitted a deprecation warning
             assert len(w) == 1
             assert issubclass(w[0].category, DeprecationWarning)
-            assert "session_lifespan parameter is deprecated" in str(w[0].message)
-            assert "use the lifespan parameter instead" in str(w[0].message)
+            assert "lifespan parameter is deprecated" in str(w[0].message)
+            assert "use the session_lifespan parameter instead" in str(w[0].message)
 
-    async def test_session_lifespan_still_works(self):
+    async def test_lifespan_still_works(self):
         """Test that session_lifespan still functions despite deprecation."""
-        session_events = []
+        session_events: list[str] = []
 
         @asynccontextmanager
         async def session_lifespan(mcp: FastMCP) -> AsyncIterator[None]:
@@ -118,7 +118,7 @@ async def session_lifespan(mcp: FastMCP) -> AsyncIterator[None]:
 
         with warnings.catch_warnings():
             warnings.simplefilter("ignore")
-            mcp = FastMCP("TestServer", session_lifespan=session_lifespan)
+            mcp = FastMCP("TestServer", lifespan=session_lifespan)
 
         @mcp.tool
         def test_tool() -> str:
@@ -183,7 +183,8 @@ async def server_lifespan(mcp: FastMCP) -> AsyncIterator[None]:
             yield
 
         with pytest.raises(
-            ValueError, match="Cannot specify both session_lifespan and server_lifespan"
+            expected_exception=ValueError,
+            match="Cannot specify both",
         ):
             _ = FastMCP(
                 name="TestServer",
@@ -200,15 +201,15 @@ async def my_lifespan(mcp: FastMCP) -> AsyncIterator[None]:
 
         with pytest.raises(
             expected_exception=ValueError,
-            match="Cannot specify both session_lifespan and server_lifespan",
+            match="Cannot specify both",
         ):
             _ = FastMCP(
                 name="TestServer", lifespan=my_lifespan, server_lifespan=my_lifespan
             )
 
         with pytest.raises(
             expected_exception=ValueError,
-            match="Cannot specify both session_lifespan and server_lifespan",
+            match="Cannot specify both",
         ):
             _ = FastMCP(
                 name="TestServer",