typeCast Next type appears to be incorrect

[bbugh]

Problem

The current return type of Next is void. This led to a bug in the code because as currently typed, the return value of next appears to be unnecessary.

node-mysql2/typings/mysql/lib/parsers/typeCast.d.ts

Lines 52 to 54 in 9ba3706

	export type Next = () => void;
	export type TypeCast = ((field: Field, next: Next) => any) | boolean;

I discovered in my code that unless next() was returned, this function would result in many undefined values. However, in every case that I can find it, next is called as return next(). If it is not returned, the result is empty data.

// bad, results in all `undefined` values:
typeCast: (field, next) => { next() }

// good, returns expected results
typeCast: (field, next) => { return next() }

Additionally, typescript-eslint correctly raises an error on this with the @typescript-eslint/no-confusing-void-expression rule:

Example 1

Example 2

Proposed solution

Since the return value is required, but the type is not known, the unknown type seems like the most correct option here. I tested and this resolves the issue.

mysql2/typings/mysql/lib/parsers/typeCast.d.ts
-export type Next = () => void;
+export type Next = () => unknown;

I can submit a PR if requested (and it will be accepted).

[wellwelwel]

// good, returns expected results
typeCast: (field, next) => { return next() }

@bbugh, could you help with a basic debug (if you can't, I'll try to check it out later)?

What would console.log(next()) return in general or when would it return something other than void | undefined?

[bbugh]

console.log(next()) will print whatever the value of the field is. I don't think it should ever be void:

"a3adef49-a125-5e83-bc84-0a9f57f5b167"
"5b455423-7961-53b7-a627-93db69ab295c"
"ac4233ad-b60e-5ce9-9185-3d366815348c"
4

---

Here is further demonstration of the issue. The console output of the following code when typeCast next return value is not or is returned:

const [rows] = await connection.query(sql, values);
console.log(rows);

❌ Without returning next, no fields have values

typeCast: (field, next) => { next(); }, // notice no "return"

{
  id: undefined,
  projectId: undefined,
  taskId: undefined,
  status: undefined,
},
{
  id: undefined,
  projectId: undefined,
  taskId: undefined,
  status: undefined,
}

✅ With returning next, it returns the field values

typeCast: (field, next) => { return next() },

{
  id: "a3adef49-a125-5e83-bc84-0a9f57f5b167",
  projectId: "5b455423-7961-53b7-a627-93db69ab295c",
  taskId: "ac4233ad-b60e-5ce9-9185-3d366815348c",
  status: 4,
},
{
  id: "cf483a80-52a0-5f53-8b24-03dc9d6dc60c",
  projectId: "01b821bf-e4a8-5953-8d59-72d1a28b4543",
  taskId: "2a803da9-b6c6-5746-989b-ca07832d0a72",
  status: 2,
}

[wellwelwel]

Thanks for the debug, @bbugh 🤝

I can submit a PR if requested (and it will be accepted).

Please, feel free to contribute 🚀