Cannot build crate on latest nightly (Win 10)

[ManifoldFR]

🐛 Bug Reports

🌍 Environment

• Your operating system and version: Windows 10 Home (build 17134)
• Your python version: 3.6.6 (Anaconda 5.1)
• Your rust version (rustc --version): latest nightly, rustc 1.29.0-nightly (866a71325 2018-07-29), windows-gnu toolchain. I also checked on the MSVC toolchain.

💥 Reproducing

The issue can be reproduced with the above steps

cargo new --lib pyo3test
cd pyo3test
cargo build

It will error out upon building pyo3 v0.3.2, with Error code 119 about conflicting implementations of the the python::IntoPyDictPointer trait for several types (such as (_, _), or (_, _, _), and so on), as goes:

error[E0119]: conflicting implementations of trait `python::IntoPyDictPointer` for type `(_, _)`:
   --> C:\Users\MyUsername\.cargo\registry\src\github.com-1ecc6299db9ec823\pyo3-0.3.2\src\objects\dict.rs:246:1
    |
231 | / impl <K, V, I> IntoPyDictPointer for I
232 | | where
233 | |     K: ToPyObject,
234 | |     V: ToPyObject,
...   |
243 | |     }
244 | | }
    | |_- first implementation here
245 |
246 |   impl<K: ToPyObject, V: ToPyObject> IntoPyDictPointer for (K, V) {
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(_, _)`
    |
    = note: upstream crates may add new impl of trait `std::iter::Iterator` for type `(_, _)` in future versions

I'll probably roll back to a previous Rust build (I updated today), but this might need some looking into if some breaking changes are coming in

[konstin]

Yep, that's due to rust-lang/rust#52050. I'm looking into it. The tl;dr is that this should have never compiled but passed due to a bug in specialization.

[konstin]

I've fixed this by removing the tuple to PyDict as owned pointer conversions. Even though I expect no one has been using those weird functions, it's technically a semver breaking change and I've released the fixed version as 0.4.0. Everything should compile again after upgrading to 0.4.0.