Self not supported in fallible builders (as return type of constructor)

[d4h0]

Hi,

First of all, thanks for building buildstructor!

I like the chosen approach quite a lot.

I noticed, that the Self type alias isn't supported, when defining a fallible builder:

// Works:
pub struct Foo {
    foo: (),
}

#[buildstructor::builder]
impl Foo {
    pub fn new(foo: ()) -> Self { // <- `Self`
        Self { foo }
    }
}

// Doesn't work:
pub struct Bar {
    bar: (),
}

#[buildstructor::builder]
impl Bar {
    pub fn new(bar: ()) -> Result<Self, ()> { // <- `Self`
        Ok(Self { bar })
    }
}

// Works:
pub struct Baz {
    baz: (),
}

#[buildstructor::builder]
impl Baz {
    pub fn new(baz: ()) -> Result<Baz, ()> { // <- no `Self`
        Ok(Self { baz })
    }
}

The resulting error is as follows:

error[E0308]: mismatched types
  --> my_crate/main.rs:30:1
   |
30 | #[buildstructor::builder]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `__BarBuilder`, found struct `rustdoc::Bar`
31 | impl Bar {
32 |     pub fn new(bar: ()) -> Result<Self, ()> {
   |                            ---------------- expected `Result<__BarBuilder<(__P0,)>, ()>` because of return type
   |
   = note: expected enum `Result<__BarBuilder<(__P0,)>, _>`
              found enum `Result<rustdoc::Bar, _>`
   = note: this error originates in the attribute macro `buildstructor::builder` (in Nightly builds, run with -Z macro-backtrace for more info)

...which is a bit confusing, to be honest... ;)

[BrynCooke]

Hi.
Thanks for the detailed bug report!

I'll get round to this in the next couple of weeks.

Not sure what can be done about error messages, the generated code is not pleasant, and only testing and time is going to surface issues. Hopefully I'll get some time to improve things over the coming months.

[d4h0]

Sounds good. Thank you, @BrynCooke.