fix: preserve valid servers during CLI discovery (#4714)

Co-authored-by: Shuying <zsy@u.northwestern.edu>

fastmcp_slim/fastmcp/cli/discovery.py

@@ -97,24 +97,33 @@ def _parse_mcp_servers(
     if not servers_dict:
         return []
 
-    normalized = {
-        name: _normalize_server_entry(entry)
-        for name, entry in servers_dict.items()
-        if isinstance(entry, dict)
-    }
+    discovered: list[DiscoveredServer] = []
+    for name, entry in servers_dict.items():
+        if not isinstance(entry, dict):
+            continue
 
-    try:
-        config = MCPConfig.from_dict({"mcpServers": normalized})
-    except Exception as exc:
-        logger.warning("Could not parse MCP servers from %s: %s", config_path, exc)
-        return []
+        normalized = _normalize_server_entry(entry)
+        try:
+            config = MCPConfig.from_dict({"mcpServers": {name: normalized}})
+        except Exception as exc:
+            logger.warning(
+                "Could not parse MCP server %r from %s: %s",
+                name,
+                config_path,
+                exc,
+            )
+            continue
 
-    return [
-        DiscoveredServer(
-            name=name, source=source, config=server, config_path=config_path
+        discovered.append(
+            DiscoveredServer(
+                name=name,
+                source=source,
+                config=config.mcpServers[name],
+                config_path=config_path,
+            )
         )
-        for name, server in config.mcpServers.items()
-    ]
+
+    return discovered
 
 
 def _parse_mcp_config(path: Path, source: str) -> list[DiscoveredServer]:

tests/cli/test_discovery.py

@@ -140,6 +140,30 @@ class TestParseMcpConfig:
         servers = _parse_mcp_config(path, "test")
         assert servers == []
 
+    def test_invalid_server_does_not_hide_valid_servers(
+        self, tmp_path: Path, caplog: pytest.LogCaptureFixture
+    ):
+        path = tmp_path / "config.json"
+        _write_config(
+            path,
+            {
+                "mcpServers": {
+                    "working": {
+                        "command": "python",
+                        "args": ["server.py"],
+                    },
+                    "broken": {
+                        "args": ["missing-command.py"],
+                    },
+                }
+            },
+        )
+
+        servers = _parse_mcp_config(path, "test")
+
+        assert [server.name for server in servers] == ["working"]
+        assert "broken" in caplog.text
+
     def test_remote_server(self, tmp_path: Path):
         path = tmp_path / "config.json"
         _write_config(path, _REMOTE_CONFIG)