Impossible type generated for tagged enum variant with anonymous field

[link2xt]

I have tried adding this test:

diff --git a/tests/test.rs b/tests/test.rs
index cc14ae8..5480c3a 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -246,6 +246,7 @@ export type Test10=({"type":"A";"value":(types.Parent&{"a":string;"b":types.Usiz
                 B(Inner),
                 // C(Inner, Inner), // not allowed
                 D,
+                E(i64),
             }
 
             assert_eq_str!(

This results in generation of the following type:

export type I64=number;
export type Test=(({"type":"A";}&{"a":types.Inner;})|({"type":"B";}&types.Inner)|{"type":"D";}|({"type":"E";}&types.I64));

Type ({"type":"E";}&types.I64) does not look like something possible to construct.

This is a minimal example of what I am trying to do at deltachat/deltachat-core-rust#4602

No idea how this type should look like, maybe should not be allowed similar to C.

[dbeckwith]

A type like this is not even supported by serde_json. When I try to serialize a value of this type, I get an error cannot serialize tagged newtype variant Test::E containing an integer. Since the goal of this library is to produce TypeScript types that describe the way serde_json serializes values, ({"type":"E";}&types.I64) is technically correct because its effectively never, and serde_json cannot serialize values of this type.

Maybe I could update my library to catch this case and throw an error or emit never just as a quality-of-life improvement though.

[dbeckwith]

That same test has a commented-out variant // C(Inner, Inner), // not allowed demonstrating another valid Rust type that serde_json does not support (and neither does this library, although it may emit nonsensical types for it).

[dbeckwith]

Thinking about how I might catch this case in my library, I think it's not possible to do statically since it's hard to tell in general if the type i64 in E(i64) is a struct or a primitive. I think this is the same reason serde doesn't emit an error in its derive macro for this case, but it does for C(Inner, Inner).