use min_specialization for some rustc crates where it requires no changes

[RalfJung]

and add FIXME for the rest

Cc @matthewjasper

[rust-highfive]

r? @varkor

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[RalfJung]

@matthewjasper ICEs shouldn't happen, should they?

error: internal compiler error: src/librustc_trait_selection/traits/specialize/mod.rs:101: When translating substitutions for specialization, the expected specialization failed to hold

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:904:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[matthewjasper]

They shouldn't, but the feature has pretty limited testing.

[matthewjasper]

Can you test libserialize as well?

[RalfJung]

Ah I only grepped in libr*and missed that one... on it.

[RalfJung]

Nope that did not work.

error: cannot specialize on trait `serialize::Encodable`
   --> src/libserialize/serialize.rs:644:1
    |
644 | / impl<T: ?Sized + Encodable> Encodable for Box<T> {
645 | |     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
646 | |         (**self).encode(s)
647 | |     }
648 | | }
    | |_^

error: cannot specialize on trait `serialize::Decodable`
   --> src/libserialize/serialize.rs:650:1
    |
650 | / impl<T: Decodable> Decodable for Box<T> {
651 | |     fn decode<D: Decoder>(d: &mut D) -> Result<Box<T>, D::Error> {
652 | |         Ok(box Decodable::decode(d)?)
653 | |     }
654 | | }
    | |_^

And if I mark those as specializable then tons of other impls fail.

[matthewjasper]

@bors r+ rollup

[bors]

📌 Commit 6f5310bdb207439d8f1ca6f17ed22c158e14339e has been approved by matthewjasper

[bors]

☔ The latest upstream changes (presumably #72041) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC-zz]

@bors r-

[RalfJung]

rebased
@bors r=matthewjasper

[bors]

📌 Commit c82103c has been approved by matthewjasper