New `HashMap` export type creates type problems

[timephy]

Hello! Long time no see.
I've just upgraded past 10.0.0 with this breaking change:

Change how HashMap<K, V> is represented in TypeScript. The resulting bindings ({ [key in K]?: V } instead of { [key: K]: V }) are more accurate and flexible.

This does create problems, because now inside a Object.values(...)/Object.entries(...) the value can be undefined. Which it is definitely not.

Either using HashMap<K, V> or { [key: K]: V }) would prevent this problem.

I cannot quite understand why that decision was made.
But all I ask for is a feature flag to change this please. 🙏🏽
(for me this has created >25 errors in my repo - all wrongfully, because undefined is never the case)

[gustavo-shigueo]

Hey @timephy, nice to see you again!

I cannot quite understand why that decision was made.

The main reason is described in #337. { [key: K]: V } does not allow K to be an enum ('A' | 'B' | 'C')

Fixing this is relatively simple, since we just need to change : to in ({ [key in K]: V }) but this brings a new problem: now all variants of your enum are required in the object, so { A: 'foo' } throws a type error because keys 'B' and 'C' are missing, hence the ? to avoid this issue

What really annoys me about this problem is that TS has a config that should fix this: exactOptionalPropertyTypes

[gustavo-shigueo]

@NyxCode, what do you think about adding a method to the TS interface?

Default impl:

trait TS {
  /* ... */
  
  fn as_hashmap_key(&self) -> String {
    format!("[key: {}]", self.name())
  }
}

Impl when the type is an enum:

fn as_hashmap_key(&self) -> String {
  format("[key in {}]?", self.name())
}

Or maybe just a const

Default impl:

trait TS {
  const IS_HASHMAP_OPTIONAL: bool = false;

  /* ... */
}

Impl when the type is an enum:

  const IS_HASHMAP_OPTIONAL: bool = true;

Then in the HashMap TS impl we could do

  format!(
    "{{ [key in {}]{}: {} }}",
    K::name(),
    if K::IS_HASHMAP_OPTIONAL { "?" } else { "" },
    V::name()
  )

[timephy]

Oh wow, I didn't even know about exactOptionalPropertyTypes!
I gave it a try but of course ran into the same thing as you.
According to the docs it does prevent writing to the property, but does not improve/fix the type for reading... What a scam 😂

Thanks for looking into this! I would appreciate a "fix" for HashMaps 🙏🏽
(I downgraded to 9.0.1 for now)

[NyxCode]

These record types are just a recurring nightmare at this point. Yikes.
I like the solution you propose though - fallback to the old behavior for normal structs!