Compile error deriving FromForm on a struct made by a macro

[MassiminoilTrace]

Hello
I post this here instead of the issues section because i'm not sure if it's my mistake, if it happens because of my little knowledge of fromform inner algorithm or if it is a rocket limitation.
Should i move it to the issues or keep it here?

I tried deriving things different than FromForm and they all work ( I tried deriving Clone, serde's Serialize and Deserialize).

I reduced it to a very simple example that still fails to compile.

Reproducing
Create a macro that takes a struct and simply declares each field, a sort of "wrapper" like in this website. My previous macro did other stuff like generating getter and setters from this and some other stuff, but I removed that part to make an barebone example.

macro_rules! test {
    (
        $(#[$meta:meta])*
        $vis:vis struct $struct_name:ident
        {
            $(
                $field_vis:vis $field_name:ident : $field_type:ty
            ),*
        }
    ) =>
    {
        $(#[$meta])*
        $vis struct $struct_name
        {
            $(
                $field_name: $field_type
            )*,
        }
    }
}

Then I simply use the example macro while deriving FromForm

test!(
    #[derive(FromForm)]
    struct Abc
    {
        a: u32
    }
);

Error message
Compile error saying:

error[E0425]: cannot find value `__c` in this scope
  --> src/main.rs:18:30
   |
18 |                   $field_name: $field_type
   |                                ^^^^^^^^^^^ not found in this scope
...
26 | / test!(
27 | |     #[derive(FromForm)]
28 | |     struct Abc
29 | |     {
30 | |         a: u32
31 | |     }
32 | | );
   | |_- in this macro invocation
   |
   = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0425]: cannot find value `__f` in this scope
  --> src/main.rs:18:30
   |
18 |                   $field_name: $field_type
   |                                ^^^^^^^^^^^ not found in this scope
...
26 | / test!(
27 | |     #[derive(FromForm)]
28 | |     struct Abc
29 | |     {
30 | |         a: u32
31 | |     }
32 | | );
   | |_- in this macro invocation
   |
   = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0425]: cannot find value `__c` in this scope
  --> src/main.rs:16:9
   |
16 | /         {
17 | |             $(
18 | |                 $field_name: $field_type
19 | |             )*,
20 | |         }
   | |_________^ not found in this scope
...
26 | / test!(
27 | |     #[derive(FromForm)]
28 | |     struct Abc
29 | |     {
30 | |         a: u32
31 | |     }
32 | | );
   | |_- in this macro invocation
   |
   = note: this error originates in the macro `test` (in Nightly builds, run with -Z macro-backtrace for more info)