fix(arcjet): Infer types when no detect function is specified

[blaine-arcjet]

While trying to improve the type inference on #1358, I found that we weren't providing the correct type inference on the sensitiveInfo rule when a user does not specify a detect() function. This is likely the most common scenario so we want to have proper type inference here.

To solve this, I made Detect very generic throughout the types and then used some techniques (commented inline) to figure out if the function was specified in the options.

[trunk-io]

😎 Merged successfully - details.

[blaine-arcjet]

There's a really annoying behavior with this type inference. When the detect property is specified, it needs to use a colon and can't be the object function shorthand syntax. Such that:

const [rule] = sensitiveInfo({
        mode: "LIVE",
        allow: ["custom", "CREDIT_CARD_NUMBER"],
// WORKS
        detect: (tokens: string[]) => {
          return tokens.map((token) => {
            if (token === "[email protected]") {
              return "custom";
            }
          });
        },
        contextWindowSize: 1,
});

const [rule] = sensitiveInfo({
        mode: "LIVE",
        allow: ["custom", "CREDIT_CARD_NUMBER"],
// FAILS
        detect(tokens: string[]) {
          return tokens.map((token) => {
            if (token === "[email protected]") {
              return "custom";
            }
          });
        },
        contextWindowSize: 1,
});

I can't figure out how to make TypeScript support both so that's just a caveat here.

[blaine-arcjet]

I think this has the other caveat I found in #1358 (comment):

I've also just discovered that the arguments of detect must be typed as string[] otherwise the inference is lost. I need think more about how to solve that.