Expected type to be "Array<Json>", but got "Array<Json>" instead

[Chriscbr]

I tried this:

let extra = MutArray<Json>["bar"];
let base = [Json "foo"];
base.concat(extra.copy());

This happened:

error: Expected type to be "Array<Json>", but got "Array<Json>" instead
  --> main.w:3:13
  |
3 | base.concat(extra.copy());
  |              ^^^^^^^^^^ Expected type to be "Array<Json>", but got "Array<Json>" instead

I expected this:

No error

Is there a workaround?

If I change the second statement to

let base = Array<Json>["foo"];

then it compiles.

Anything else?

No response

Wing Version

0.54.28

Node.js Version

20.9.0

Platform(s)

MacOS

Community Notes

• Please vote by adding a 👍 reaction to the issue to help us prioritize.
• If you are interested to work on this issue, please leave a comment.

[Chriscbr]

The error is similar the one in #3822, but it might not be the same cause

[Chriscbr]

Another variation:

let base = Array<Json>["foo"];

let obj = {
  first: "ok",
  second: ["cool"].concat(base)
};

Here's the error it produces today

error: Expected type to be "Array<Json>", but got "Array<Json>" instead
  --> main.w:5:27
  |
5 |   second: ["cool"].concat(base)
  |                           ^^^^ Expected type to be "Array<Json>", but got "Array<Json>" instead

In principle this code should also compile if base is annotated as Array<str>.

[Chriscbr]

Another example

let arr = MutArray<num>[1, 2, 3];
arr.push(4);

let takeJson = (obj: Json) => {
  // ...
};

takeJson({ values: arr });

yields:

Failed to compile.

error: Expected type to be "Json", but got "Json" instead
  --> wing/main.w:8:10
  |
8 | takeJson({ values: arr });
  |          ^^^^^^^^^^^^^^^


error: "MutArray<num>" is not a legal JSON value
  --> wing/main.w:8:20
  |
8 | takeJson({ values: arr });
  |                    ^^^

The easiest fix is to convert the MutArray to a plain Array by calling .copy(), but the error message should be improved

[monadabot]

Congrats! 🚀 This was released in Wing 0.82.3.