ci: add strict-no-cover to detect unnecessary coverage pragmas (#1897)

Author: maxisbey

.github/workflows/shared.yml

@@ -62,6 +62,10 @@ jobs:
           uv run --frozen --no-sync coverage combine
           uv run --frozen --no-sync coverage report
 
+      - name: Check for unnecessary no cover pragmas
+        if: runner.os != 'Windows'
+        run: uv run --frozen --no-sync strict-no-cover
+
   readme-snippets:
     runs-on: ubuntu-latest
     steps:

pyproject.toml

@@ -66,8 +66,9 @@ dev = [
     "pytest-pretty>=1.2.0",
     "inline-snapshot>=0.23.0",
     "dirty-equals>=0.9.0",
-    "coverage[toml]>=7.13.1",
+    "coverage[toml]>=7.10.7,<=7.13",
     "pillow>=12.0",
+    "strict-no-cover",
 ]
 docs = [
     "mkdocs>=1.6.1",
@@ -163,6 +164,7 @@ members = ["examples/clients/*", "examples/servers/*", "examples/snippets"]
 
 [tool.uv.sources]
 mcp = { workspace = true }
+strict-no-cover = { git = "https://github.com/pydantic/strict-no-cover" }
 
 [tool.pytest.ini_options]
 log_cli = true
@@ -198,7 +200,6 @@ branch = true
 patch = ["subprocess"]
 concurrency = ["multiprocessing", "thread"]
 source = ["src", "tests"]
-relative_files = true
 omit = [
     "src/mcp/client/__main__.py",
     "src/mcp/server/__main__.py",
@@ -215,6 +216,7 @@ ignore_errors = true
 precision = 2
 exclude_lines = [
     "pragma: no cover",
+    "pragma: lax no cover",
     "if TYPE_CHECKING:",
     "@overload",
     "raise NotImplementedError",

src/mcp/cli/claude.py

@@ -72,7 +72,7 @@ def update_claude_config(
         )
 
     config_file = config_dir / "claude_desktop_config.json"
-    if not config_file.exists():  # pragma: no cover
+    if not config_file.exists():  # pragma: lax no cover
         try:
             config_file.write_text("{}")
         except Exception:

src/mcp/cli/cli.py

@@ -77,7 +77,7 @@ def _build_uv_command(
 
     if with_packages:
         for pkg in with_packages:
-            if pkg:  # pragma: no cover
+            if pkg:  # pragma: no branch
                 cmd.extend(["--with", pkg])
 
     # Add mcp run command

src/mcp/client/auth/oauth2.py

@@ -192,7 +192,7 @@ def prepare_token_auth(
             headers = {}  # pragma: no cover
 
         if not self.client_info:
-            return data, headers  # pragma: no cover
+            return data, headers
 
         auth_method = self.client_info.token_endpoint_auth_method
 
@@ -418,7 +418,7 @@ async def _refresh_token(self) -> httpx.Request:
             raise OAuthTokenError("No client info available")  # pragma: no cover
 
         if self.context.oauth_metadata and self.context.oauth_metadata.token_endpoint:
-            token_url = str(self.context.oauth_metadata.token_endpoint)  # pragma: no cover
+            token_url = str(self.context.oauth_metadata.token_endpoint)
         else:
             auth_base_url = self.context.get_authorization_base_url(self.context.server_url)
             token_url = urljoin(auth_base_url, "/token")
@@ -534,7 +534,7 @@ async def async_auth_flow(self, request: httpx.Request) -> AsyncGenerator[httpx.
                     )
 
                     # Step 2: Discover OAuth Authorization Server Metadata (OASM) (with fallback for legacy servers)
-                    for url in asm_discovery_urls:  # pragma: no cover
+                    for url in asm_discovery_urls:  # pragma: no branch
                         oauth_metadata_request = create_oauth_metadata_request(url)
                         oauth_metadata_response = yield oauth_metadata_request
 

src/mcp/client/session.py

@@ -250,7 +250,7 @@ async def set_logging_level(
         meta: RequestParamsMeta | None = None,
     ) -> types.EmptyResult:
         """Send a logging/setLevel request."""
-        return await self.send_request(  # pragma: no cover
+        return await self.send_request(
             types.SetLevelRequest(params=types.SetLevelRequestParams(level=level, _meta=meta)),
             types.EmptyResult,
         )
@@ -285,14 +285,14 @@ async def read_resource(self, uri: str, *, meta: RequestParamsMeta | None = None
 
     async def subscribe_resource(self, uri: str, *, meta: RequestParamsMeta | None = None) -> types.EmptyResult:
         """Send a resources/subscribe request."""
-        return await self.send_request(  # pragma: no cover
+        return await self.send_request(
             types.SubscribeRequest(params=types.SubscribeRequestParams(uri=uri, _meta=meta)),
             types.EmptyResult,
         )
 
     async def unsubscribe_resource(self, uri: str, *, meta: RequestParamsMeta | None = None) -> types.EmptyResult:
         """Send a resources/unsubscribe request."""
-        return await self.send_request(  # pragma: no cover
+        return await self.send_request(
             types.UnsubscribeRequest(params=types.UnsubscribeRequestParams(uri=uri, _meta=meta)),
             types.EmptyResult,
         )
@@ -344,7 +344,7 @@ async def _validate_tool_result(self, name: str, result: types.CallToolResult) -
             try:
                 validate(result.structured_content, output_schema)
             except ValidationError as e:
-                raise RuntimeError(f"Invalid structured content returned by tool {name}: {e}")  # pragma: no cover
+                raise RuntimeError(f"Invalid structured content returned by tool {name}: {e}")
             except SchemaError as e:  # pragma: no cover
                 raise RuntimeError(f"Invalid schema for tool {name}: {e}")  # pragma: no cover
 

src/mcp/client/session_group.py

@@ -223,22 +223,22 @@ async def disconnect_from_server(self, session: mcp.ClientSession) -> None:
                 )
             )
 
-        if session_known_for_components:  # pragma: no cover
+        if session_known_for_components:  # pragma: no branch
             component_names = self._sessions.pop(session)  # Pop from _sessions tracking
 
             # Remove prompts associated with the session.
             for name in component_names.prompts:
-                if name in self._prompts:
+                if name in self._prompts:  # pragma: no branch
                     del self._prompts[name]
             # Remove resources associated with the session.
             for name in component_names.resources:
-                if name in self._resources:
+                if name in self._resources:  # pragma: no branch
                     del self._resources[name]
             # Remove tools associated with the session.
             for name in component_names.tools:
-                if name in self._tools:
+                if name in self._tools:  # pragma: no branch
                     del self._tools[name]
-                if name in self._tool_to_session:
+                if name in self._tool_to_session:  # pragma: no branch
                     del self._tool_to_session[name]
 
         # Clean up the session's resources via its dedicated exit stack

src/mcp/client/sse.py

@@ -119,12 +119,12 @@ async def sse_reader(task_status: TaskStatus[str] = anyio.TASK_STATUS_IGNORED):
                                         await read_stream_writer.send(session_message)
                                     case _:  # pragma: no cover
                                         logger.warning(f"Unknown SSE event: {sse.event}")  # pragma: no cover
-                        except SSEError as sse_exc:  # pragma: no cover
-                            logger.exception("Encountered SSE exception")  # pragma: no cover
-                            raise sse_exc  # pragma: no cover
-                        except Exception as exc:  # pragma: no cover
-                            logger.exception("Error in sse_reader")  # pragma: no cover
-                            await read_stream_writer.send(exc)  # pragma: no cover
+                        except SSEError as sse_exc:  # pragma: lax no cover
+                            logger.exception("Encountered SSE exception")
+                            raise sse_exc
+                        except Exception as exc:  # pragma: lax no cover
+                            logger.exception("Error in sse_reader")
+                            await read_stream_writer.send(exc)
                         finally:
                             await read_stream_writer.aclose()
 
@@ -143,8 +143,8 @@ async def post_writer(endpoint_url: str):
                                     )
                                     response.raise_for_status()
                                     logger.debug(f"Client message sent successfully: {response.status_code}")
-                        except Exception:  # pragma: no cover
-                            logger.exception("Error in post_writer")  # pragma: no cover
+                        except Exception:  # pragma: lax no cover
+                            logger.exception("Error in post_writer")
                         finally:
                             await write_stream.aclose()
 

src/mcp/client/stdio.py

@@ -56,8 +56,8 @@ def get_default_environment() -> dict[str, str]:
 
     for key in DEFAULT_INHERITED_ENV_VARS:
         value = os.environ.get(key)
-        if value is None:
-            continue  # pragma: no cover
+        if value is None:  # pragma: lax no cover
+            continue
 
         if value.startswith("()"):  # pragma: no cover
             # Skip functions, which are a security risk
@@ -158,7 +158,7 @@ async def stdout_reader():
 
                         session_message = SessionMessage(message)
                         await read_stream_writer.send(session_message)
-        except anyio.ClosedResourceError:  # pragma: no cover
+        except anyio.ClosedResourceError:  # pragma: lax no cover
             await anyio.lowlevel.checkpoint()
 
     async def stdin_writer():
@@ -225,8 +225,8 @@ def _get_executable_command(command: str) -> str:
     """
     if sys.platform == "win32":  # pragma: no cover
         return get_windows_executable_command(command)
-    else:
-        return command  # pragma: no cover
+    else:  # pragma: lax no cover
+        return command
 
 
 async def _create_platform_compatible_process(
@@ -243,14 +243,14 @@ async def _create_platform_compatible_process(
     """
     if sys.platform == "win32":  # pragma: no cover
         process = await create_windows_process(command, args, env, errlog, cwd)
-    else:
+    else:  # pragma: lax no cover
         process = await anyio.open_process(
             [command, *args],
             env=env,
             stderr=errlog,
             cwd=cwd,
             start_new_session=True,
-        )  # pragma: no cover
+        )
 
     return process
 
@@ -267,7 +267,7 @@ async def _terminate_process_tree(process: Process | FallbackProcess, timeout_se
     """
     if sys.platform == "win32":  # pragma: no cover
         await terminate_windows_process_tree(process, timeout_seconds)
-    else:  # pragma: no cover
+    else:  # pragma: lax no cover
         # FallbackProcess should only be used for Windows compatibility
         assert isinstance(process, Process)
         await terminate_posix_process_tree(process, timeout_seconds)

src/mcp/client/streamable_http.py

@@ -181,7 +181,7 @@ async def handle_get_stream(self, client: httpx.AsyncClient, read_stream_writer:
 
                 headers = self._prepare_headers()
                 if last_event_id:
-                    headers[LAST_EVENT_ID] = last_event_id  # pragma: no cover
+                    headers[LAST_EVENT_ID] = last_event_id
 
                 async with aconnect_sse(client, "GET", self.url, headers=headers) as event_source:
                     event_source.response.raise_for_status()
@@ -190,17 +190,17 @@ async def handle_get_stream(self, client: httpx.AsyncClient, read_stream_writer:
                     async for sse in event_source.aiter_sse():
                         # Track last event ID for reconnection
                         if sse.id:
-                            last_event_id = sse.id  # pragma: no cover
+                            last_event_id = sse.id
                         # Track retry interval from server
                         if sse.retry is not None:
-                            retry_interval_ms = sse.retry  # pragma: no cover
+                            retry_interval_ms = sse.retry
 
                         await self._handle_sse_event(sse, read_stream_writer)
 
                     # Stream ended normally (server closed) - reset attempt counter
                     attempt = 0
 
-            except Exception as exc:  # pragma: no cover
+            except Exception as exc:  # pragma: lax no cover
                 logger.debug(f"GET stream error: {exc}")
                 attempt += 1
 
@@ -333,8 +333,8 @@ async def _handle_sse_response(
                 if is_complete:
                     await response.aclose()
                     return  # Normal completion, no reconnect needed
-        except Exception as e:  # pragma: no cover
-            logger.debug(f"SSE stream ended: {e}")
+        except Exception as e:
+            logger.debug(f"SSE stream ended: {e}")  # pragma: no cover
 
         # Stream ended without response - reconnect if we received an event with ID
         if last_event_id is not None:  # pragma: no branch
@@ -472,20 +472,20 @@ async def handle_request_async():
             await read_stream_writer.aclose()
             await write_stream.aclose()
 
-    async def terminate_session(self, client: httpx.AsyncClient) -> None:  # pragma: no cover
+    async def terminate_session(self, client: httpx.AsyncClient) -> None:
         """Terminate the session by sending a DELETE request."""
-        if not self.session_id:
+        if not self.session_id:  # pragma: lax no cover
             return
 
         try:
             headers = self._prepare_headers()
             response = await client.delete(self.url, headers=headers)
 
-            if response.status_code == 405:
+            if response.status_code == 405:  # pragma: lax no cover
                 logger.debug("Server does not allow session termination")
-            elif response.status_code not in (200, 204):
+            elif response.status_code not in (200, 204):  # pragma: lax no cover
                 logger.warning(f"Session termination failed: {response.status_code}")
-        except Exception as exc:
+        except Exception as exc:  # pragma: no cover
             logger.warning(f"Session termination failed: {exc}")
 
     def get_session_id(self) -> str | None: