Problem replacing dummy trait methods

[xunilrj]

The code below is triggering the following error:

 error
           --> /home/xunilrj/github/sway/test/src/e2e_vm_tests/test_programs/should_pass/language/main_args/main_args_empty/src/main.sw:4:8
            |
          2 | 
          3 | trait AbiEncode2 {
          4 |     fn abi_encode2(self, ref mut buffer: Buffer);
            |        ^^^^^^^^^^^ Internal compiler error: Method abi_encode2_3 is a trait method dummy and was not properly replaced.
          Please file an issue on the repository and include the code that triggered this error.
          5 | }
            |
          ____

            Aborting due to 1 error.

The code. This is a simplified version of the new encoding that is being implemented.

script;

trait AbiEncode2 {
    fn abi_encode2(self, ref mut buffer: Buffer);
}

impl AbiEncode2 for u64 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u32 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u16 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u8 { fn abi_encode2(self, ref mut buffer: Buffer) { } }

struct GenericBimbam<U> {
    val: U,
}

impl<U> AbiEncode2 for GenericBimbam<U> where U: AbiEncode2,
 {
    fn abi_encode2(self, ref mut buffer: Buffer) {
        self.val.abi_encode2(buffer);
    }
}

struct GenericSnack<T, V> {
    twix: GenericBimbam<T>,
    mars: V,
}

impl<T, V> AbiEncode2 for GenericSnack<T, V> where T: AbiEncode2, V: AbiEncode2,
 {
    fn abi_encode2(self, ref mut buffer: Buffer) {
        self.twix.abi_encode2(buffer);
        self.mars.abi_encode2(buffer);
    }
}

fn encode2<T>(item: T) -> raw_slice where T: AbiEncode2  {
    let mut buffer = Buffer::new();
    item.abi_encode2(buffer);
    buffer.as_raw_slice()
}

fn main() {
    encode2(GenericSnack { twix: GenericBimbam { val: 0u64 }, mars: 2u32 });
}

This blocks: #5427

[xunilrj]

I don't know if this is the solution for this problem, but for my PR I solved this with: be3cc06#diff-35d4b64f583b6ae57aa8095e3d3049788690e178702af2aaf6443030818b74c8R707

[tritao]

So this seems to be a problem with trait constraints and our replace decls machinery. Me and @esdrubal been looking at this and found a workaround, if you move the where clauses to the method then it seems to work fine.

script;

trait AbiEncode2 {
    fn abi_encode2(self, ref mut buffer: Buffer);
}

impl AbiEncode2 for u64 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u32 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u16 { fn abi_encode2(self, ref mut buffer: Buffer) { } }
impl AbiEncode2 for u8 { fn abi_encode2(self, ref mut buffer: Buffer) { } }

struct GenericBimbam<U> {
    val: U,
}

impl<U> AbiEncode2 for GenericBimbam<U>
 {
    fn abi_encode2(self, ref mut buffer: Buffer) where U: AbiEncode2 {
        self.val.abi_encode2(buffer);
    }
}

struct GenericSnack<T, V> {
    twix: GenericBimbam<T>,
    mars: V,
}

impl<T, V> AbiEncode2 for GenericSnack<T, V>
 {
    fn abi_encode2(self, ref mut buffer: Buffer) where T: AbiEncode2, V: AbiEncode2 {
        self.twix.abi_encode2(buffer);
        self.mars.abi_encode2(buffer);
    }
}

fn encode2<T>(item: T) -> raw_slice where T: AbiEncode2  {
    let mut buffer = Buffer::new();
    item.abi_encode2(buffer);
    buffer.as_raw_slice()
}

fn main() {
    encode2(GenericSnack { twix: GenericBimbam { val: 0u64 }, mars: 2u32 });
}

The proper bugfix for this will probably take a bit of time to get done, so hopefully this is a workable workaround so we can get this feature out ASAP.

[xunilrj]

But should this supported? Rust correctly complains that the impl has more constraints than the trait declaration

error[E0276]: impl has stricter requirements than trait
  --> src/main.rs:36:57
   |
10 |     fn abi_encode2(self, buffer: &mut Buffer);
   |     ------------------------------------------ definition of `abi_encode2` from trait
...
36 |     fn abi_encode2(self,  buffer: &mut Buffer) where T: AbiEncode2, V: AbiEncode2 {
   |                                                         ^^^^^^^^^^ impl has extra requirement `T: AbiEncode2`

[IGI-111]

Rust is right here, the signature of a trait method implementation should be the same as the trait method including the constraints. So this is exploiting a bug.

Looks like we didn't include those in the signature check when we implemented trait constraints. But we should.