Typescript 使用泛型推断正确的类型

我正在try 创建一个Reducer函数，它允许我们推断有效负载中允许的属性和值，目前这是有效的，如果调度中的type属性被更改，它将只允许传递与ToolMap相关联的值，如果在有效负载中传递错误的名称值，则将抛出错误.

问题出现在削减器的接收端，即action.有效负载不能正确地推断name属性是否正确，它总是认为它是一个联合类型CursorToolName或DrawingToolName.这让我感到有点困惑，因为当有效负载到达Switch语句中的Case时，它应该始终是正确的类型.

type ToolCategory = 'CursorTools' | 'DrawingTools'
type CursorToolName = 'Cursor' | 'Measure'
type DrawingToolName = 'Brush' | 'Pencil'


type ToolMap = {
    CursorTools: CursorToolName;
    DrawingTools: DrawingToolName
}

interface ToolState {
    CursorTools: Tool<'CursorTools'>
    DrawingTools: Tool<'DrawingTools'>
}

interface ToolAction<T extends ToolCategory>{
    type: T;
    payload: Tool<T>
}

interface Tool<T extends ToolCategory> {
    name: ToolMap[T];
    onEnter?: () => void;
}

const reducer = <T extends ToolCategory>(
    state: ToolState,
    action: ToolAction<T>
): ToolState => {
    switch(action.type){
        case 'CursorTools': {
            return {
                ...state,
                CursorTools: {
                    // This doesn't infer that the payload.name is of correct type
                    name: action.payload.name
                }
            }
        }
    }

    return state;
}

// This infers the name in the payload we can pass, and we can never pass the wrong value
reducer({CursorTools: {name: 'Cursor'}, DrawingTools: {name: 'Brush'}
}, {type: 'CursorTools', payload: {
    name: 'Cursor'
}})