implementing From<<ForeignTy as ToOwned>::Owned> for LocalTy, errors with conflicting implementation

[PizzasBear]

I tried this code:

use rand::rngs::StdRng;

#[derive(Clone)]
struct Foo;

impl From<<i32 as ToOwned>::Owned> for Foo {
    fn from(_: <i32 as ToOwned>::Owned) -> Self {
        Self
    }
}

impl From<<str as ToOwned>::Owned> for Foo {
    fn from(_: i32, _: String) -> u32 {
        Self
    }
}

impl From<<bool as ToOwned>::Owned> for Foo {
    fn from(_: <bool as ToOwned>::Owned) -> Self {
        Self
    }
    fn asdf() {}
}

impl From<<StdRng as ToOwned>::Owned> for Foo {}

#[derive(Clone)]
struct Bar;

impl From<<Bar as ToOwned>::Owned> for Foo {
    fn from(foo: <i32 as ToOwned>::Owned) -> Self {
        Self
    }
}

fn main() {}

Compiling it, I got these errors:

error[E0407]: method `asdf` is not a member of trait `From`
  --> src/main.rs:22:5
   |
22 |     fn asdf() {}
   |     ^^^^^^^^^^^^ not a member of trait `From`

error[E0119]: conflicting implementations of trait `From<Foo>` for type `Foo`
 --> src/main.rs:6:1
  |
6 | impl From<<i32 as ToOwned>::Owned> for Foo {
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: conflicting implementation in crate `core`:
          - impl<T> From<T> for T;

error[E0119]: conflicting implementations of trait `From<Foo>` for type `Foo`
  --> src/main.rs:12:1
   |
12 | impl From<<str as ToOwned>::Owned> for Foo {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: conflicting implementation in crate `core`:
           - impl<T> From<T> for T;

error[E0119]: conflicting implementations of trait `From<Foo>` for type `Foo`
  --> src/main.rs:18:1
   |
18 | impl From<<bool as ToOwned>::Owned> for Foo {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: conflicting implementation in crate `core`:
           - impl<T> From<T> for T;

error[E0119]: conflicting implementations of trait `From<Foo>` for type `Foo`
  --> src/main.rs:25:1
   |
25 | impl From<<StdRng as ToOwned>::Owned> for Foo {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: conflicting implementation in crate `core`:
           - impl<T> From<T> for T;

Some errors have detailed explanations: E0119, E0407.
For more information about an error, try `rustc --explain E0119`.
error: could not compile `test-issue` due to 5 previous errors

It seems that only structs defined in external crates trigger this error. This results in no errors about fn from() not being defined or its signature being wrong, but there is an error about other functions being defined that are not part of From.

Meta

rustc --version --verbose:

rustc 1.67.0 (fc594f156 2023-01-24)
binary: rustc
commit-hash: fc594f15669680fa70d255faec3ca3fb507c3405
commit-date: 2023-01-24
host: x86_64-unknown-linux-gnu
release: 1.67.0
LLVM version: 15.0.6

[kadiwa4]

Is this issue about the conflicting implementation or about the inconsistent error messages?

[PizzasBear]

I opened the issue mostly for the conflicting implementation, I just found the inconsistent error messages and decided to mention them here.

[Enselic]

Triage: Thanks for reporting. The code currently has quite a few problems. Can you please reduce this down to only one error? Analyzing and explaining 5 errors makes it hard to focus on what the exact issue and bug is. Thanks!