Stop panic on fmt::Display

[samuelcolvin]

Closes #3060

[adamreichold]

Any guidance on why write! isn't available, would be great.

I think you need to fully qualify it, e.g. ::std::write! which seems to work here, e.g.

impl<$($generics,)*> ::std::fmt::Display for $name {
    fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>)
            -> ::std::result::Result<(), ::std::fmt::Error>
    {
        let s = self.str().or(::std::result::Result::Err(::std::fmt::Error))?;
        ::std::write!(f, "{}", s.to_string_lossy())
    }
}

[samuelcolvin]

thanks, done.

[adamreichold]

Sorry for the many force pushes: I took a detour adding a new API

impl Python<'_> {
    pub fn try_with_gil<F, R>(f: F) -> Option<R>
    where
        F: for<'py> FnOnce(Python<'py>) -> R,
    {
        gil::try_ensure_gil().map(|gil| f(unsafe { gil.python() }))
    }
}

because I did not realise that I already had implicit access to the GIL in the Display impl. Properly removing this and fixing up the news fragment took a bit of back and forth.

[davidhewitt]

This looks good to me, thanks!

[adamreichold]

bors r=davidhewitt

[bors]

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• conclusion