TypeScript:返回类型取决于参数

Question

我有以下TypeScript函数：

declare function getUserContext(
options: UserContextOptions
): Promise<UserContext>;
declare function getTeamContext(
options: TeamContextOptions
): Promise<TeamContext>;
type UserContextWithoutSlackTeamOptions = Omit<
UserContextOptions,
'slackTeamRef'
>;
async function getContext<
T extends
| TeamContextOptions
| (TeamContextOptions & UserContextWithoutSlackTeamOptions)
>(
options: Partial<UserContextWithoutSlackTeamOptions> & T
): Promise<
T extends UserContextWithoutSlackTeamOptions
? TeamContext & UserContext
: TeamContext
> {
const teamContext = await getTeamContext(options);
const userContext = options.user
? await getUserContext({
user: options.user,
slackTeamRef: teamContext.slackTeam,
})
: undefined;
return {
...teamContext,
...userContext,
octokit: userContext.octokit ?? teamContext.octokit,
};
}

以下是接口：

interface UserContextOptions {
user: {
id: string;
name?: string;
};
slackTeamRef: string;
}
interface TeamContextOptions {
teamId: string;
}
interface TeamContext {
slackTeam: string;
octokit: string;
}
interface UserContext {
user: string | null | undefined;
slackUser: string;
octokit: string | undefined;
}

从逻辑上讲，我认为这是可行的，然而TypeScript在几个地方抱怨道：

在return声明中，它说

TS2322: Type '{ octokit: string; user?: string | null | undefined; slackUser?: string | undefined; slackTeam: string; }' is not assignable to type 'TeamContext & UserContext'.  
 Type '{ octokit: string; user?: string | null | undefined; slackUser?: string | undefined; slackTeam: string; }' is not assignable to type 'UserContext'.    
 Property 'user' is optional in type '{ octokit: string; user?: string | null | undefined; slackUser?: string | undefined; slackTeam: string; }' but required in type 'UserContext'.
TS2532: Object is possibly 'undefined'.

我看过许多其他SO职位，但我遇到的解决方案都不适用于这种特定的情况。

感谢您的帮助。

TS游乐场

Answer 1

函数重载是为这个设计的

async function getContext(options: TeamContextOptions & UserContextWithoutSlackTeamOptions): Promise<TeamContext & UserContext>;
async function getContext(options: TeamContextOptions): Promise<TeamContext>;
async function getContext(
options: TeamContextOptions & UserContextWithoutSlackTeamOptions | TeamContextOptions & Partial<UserContextWithoutSlackTeamOptions>
) {
// impl...
}
declare const teamOption: TeamContextOptions
declare const mixOption: TeamContextOptions & UserContextWithoutSlackTeamOptions
async () => {
const v1 = await getContext(teamOption) // TeamContext
const v2 = await getContext(mixOption) // TeamContext & UserContext
}