teach ClaudeCodeOptions.mcp_servers to accept a filepath (anthropics#114)

`claude`'s `--mcp-config` takes either a JSON file or string, so support
this in `ClaudeCodeOptions`
```
  --mcp-config <file or string>    Load MCP servers from a JSON file or string
```

---------

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: Sam Fu <shunfu@users.noreply.github.com>
Signed-off-by: Rushil Patel <rpatel@codegen.com>

Author: 2 people

src/claude_code_sdk/_internal/transport/subprocess_cli.py

@@ -140,9 +140,17 @@ def _build_command(self) -> list[str]:
                 cmd.extend(["--add-dir", str(directory)])
 
         if self._options.mcp_servers:
-            cmd.extend(
-                ["--mcp-config", json.dumps({"mcpServers": self._options.mcp_servers})]
-            )
+            if isinstance(self._options.mcp_servers, dict):
+                # Dict format: serialize to JSON
+                cmd.extend(
+                    [
+                        "--mcp-config",
+                        json.dumps({"mcpServers": self._options.mcp_servers}),
+                    ]
+                )
+            else:
+                # String or Path format: pass directly as file path or JSON string
+                cmd.extend(["--mcp-config", str(self._options.mcp_servers)])
 
         # Add extra args for future CLI flags
         for flag, value in self._options.extra_args.items():

src/claude_code_sdk/types.py

@@ -117,7 +117,7 @@ class ClaudeCodeOptions:
     max_thinking_tokens: int = 8000
     system_prompt: str | None = None
     append_system_prompt: str | None = None
-    mcp_servers: dict[str, McpServerConfig] = field(default_factory=dict)
+    mcp_servers: dict[str, McpServerConfig] | str | Path = field(default_factory=dict)
     permission_mode: PermissionMode | None = None
     continue_conversation: bool = False
     resume: str | None = None

tests/test_transport.py

@@ -227,3 +227,75 @@ def test_build_command_with_extra_args(self):
         boolean_idx = cmd.index("--boolean-flag")
         # Either it's the last element or the next element is another flag
         assert boolean_idx == len(cmd) - 1 or cmd[boolean_idx + 1].startswith("--")
+
+    def test_build_command_with_mcp_servers(self):
+        """Test building CLI command with mcp_servers option."""
+        import json
+
+        mcp_servers = {
+            "test-server": {
+                "type": "stdio",
+                "command": "/path/to/server",
+                "args": ["--option", "value"],
+            }
+        }
+
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=ClaudeCodeOptions(mcp_servers=mcp_servers),
+            cli_path="/usr/bin/claude",
+        )
+
+        cmd = transport._build_command()
+
+        # Find the --mcp-config flag and its value
+        assert "--mcp-config" in cmd
+        mcp_idx = cmd.index("--mcp-config")
+        mcp_config_value = cmd[mcp_idx + 1]
+
+        # Parse the JSON and verify structure
+        config = json.loads(mcp_config_value)
+        assert "mcpServers" in config
+        assert config["mcpServers"] == mcp_servers
+
+    def test_build_command_with_mcp_servers_as_file_path(self):
+        """Test building CLI command with mcp_servers as file path."""
+        from pathlib import Path
+
+        # Test with string path
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=ClaudeCodeOptions(mcp_servers="/path/to/mcp-config.json"),
+            cli_path="/usr/bin/claude",
+        )
+
+        cmd = transport._build_command()
+        assert "--mcp-config" in cmd
+        mcp_idx = cmd.index("--mcp-config")
+        assert cmd[mcp_idx + 1] == "/path/to/mcp-config.json"
+
+        # Test with Path object
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=ClaudeCodeOptions(mcp_servers=Path("/path/to/mcp-config.json")),
+            cli_path="/usr/bin/claude",
+        )
+
+        cmd = transport._build_command()
+        assert "--mcp-config" in cmd
+        mcp_idx = cmd.index("--mcp-config")
+        assert cmd[mcp_idx + 1] == "/path/to/mcp-config.json"
+
+    def test_build_command_with_mcp_servers_as_json_string(self):
+        """Test building CLI command with mcp_servers as JSON string."""
+        json_config = '{"mcpServers": {"server": {"type": "stdio", "command": "test"}}}'
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=ClaudeCodeOptions(mcp_servers=json_config),
+            cli_path="/usr/bin/claude",
+        )
+
+        cmd = transport._build_command()
+        assert "--mcp-config" in cmd
+        mcp_idx = cmd.index("--mcp-config")
+        assert cmd[mcp_idx + 1] == json_config