Conflict between Record<string, never> and Serde Tag in TypeScript Output

[bennobuilder]

Description

In Specta, an empty struct is represented as Record<string, never> in the TypeScript output, which conflicts with the Serde tag = type pattern.

Suggested Change

It's suggested to modify the handling of empty structs in TypeScript output, particularly in cases where Serde's tag is involved. Instead of using {} in general (which is not a good practice as explained in Total TypeScript - The Empty Object Type in TypeScript), the solution might involve a conditional approach based on the presence of Serde's tag.

More context: https://discord.com/channels/949090953497567312/1176756946796298310/1176761059764351127

[bennobuilder]

@oscartbeaumont

Thanks for the quick action. Though for me the proposed fix didn't work :/

Logs

--- Named: NamedFields {
    fields: [],
    tag: None,
}
--- Named: NamedFields {
    fields: [],
    tag: None,
}

Logs from

  if fields.is_empty() {
                println!("--- Named: {:#?}", s);
                return Ok(s
                    .tag()
                    .as_ref()
                    .map(|tag| format!("{{ \"{tag}\": \"{key}\" }}"))
                    .unwrap_or_else(|| format!("Record<{STRING}, {NEVER}>")));
            }

Code

#[derive(Debug, Deserialize, Type, Clone)]
#[serde(tag = "type")]
pub enum InteractionInputEvent {
    CursorEnteredComposition(CursorEnteredComposition),
    CursorExitedComposition(CursorExitedComposition),
    // ..
}

// ..

#[derive(Event, Debug, Deserialize, Type, Clone)]
pub struct CursorEnteredComposition {} // TODO: Change back to Unit struct when https://github.com/oscartbeaumont/specta/issues/174 fixed

#[derive(Event, Debug, Deserialize, Type, Clone)]
pub struct CursorExitedComposition {} // TODO: Change back to Unit struct when https://github.com/oscartbeaumont/specta/issues/174 fixed

// ..

Generated types:

export type CursorEnteredComposition = Record<string, never>

export type CursorExitedComposition = Record<string, never>

export type InteractionInputEvent = ({ type: "CursorEnteredComposition" } & CursorEnteredComposition) | ({ type: "CursorExitedComposition" } & CursorExitedComposition)

Experiment with Unit

Also it would be nice to support serde tags for Unit structs too :) (if possible)

  StructFields::Unit => {
            println!("--- Unit: {:#?}", s);
            Ok(s.tag()
                .as_ref()
                .map(|tag| format!("{{ \"{tag}\": \"{key}\" }}"))
                .unwrap_or_else(|| NULL.into())) // TODO
        }

Logs

--- Unit: StructType {
    name: "CursorEnteredComposition",
    generics: [],
    fields: Unit,
}
--- Unit: StructType {
    name: "CursorExitedComposition",
    generics: [],
    fields: Unit,
}

Thanks :)

[oscartbeaumont]

Ohhhh, now I get you.

Checking with what Serde do the expected behavior should be :

pub struct Inner {}

Previously: { "tag": "tagValue" } & Record<string, never>
Expected: { "tag":"tagValue" }

pub struct Inner

Previously: { "tag": "tagValue" } & null which Typescript coalesces to never.
Expected: { "tag":"tagValue" }

It looks like we already have a check related to this in place but it's not working correctly with references. Eg. it checks for the string null but in this case it would be Inner so the check fails.

pub struct Inner()

Previously: { "tag": "tagValue" } & []
Expected: Invalid Type Error

[oscartbeaumont]

Okay give 467e2b0 a shot and lemme know if you still are having issues.

[bennobuilder]

Okay give 467e2b0 a shot and lemme know if you still are having issues.

Seems to work as expected :)

Thanks a lot for the quick fixes 👍 🙏

export type InteractionInputEvent = ({ type: "CursorDownOnEntity" } & CursorDownOnEntity) | ({ type: "CursorMovedOnComposition" } & CursorMovedOnComposition) | ({ type: "CursorEnteredComposition" }) | ({ type: "CursorExitedComposition" })