Convert Intos to Froms.

[clarfonthey]

This didn't work before but supposedly this should work now. It's better to have From impls over Into.

[rust-highfive]

r? @BurntSushi

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[Mark-Simulacrum]

Travis failed:

[00:02:05] error[E0210]: type parameter `T` must be used as the type parameter for some local type (e.g. `MyStruct<T>`); only traits defined in the current crate can be implemented for a type parameter
[00:02:05] --> /checkout/src/libcollections/vec.rs:2128:1
[00:02:05] |
[00:02:05] 2128 | / impl<T> From<Vec<T>> for Box<[T]> {
[00:02:05] 2129 | | fn from(v: Vec<T>) -> Box<[T]> {
[00:02:05] 2130 | | v.into_boxed_slice()
[00:02:05] 2131 | | }
[00:02:05] 2132 | | }
[00:02:05] | |_^
[00:02:05]
[00:02:05] error: aborting due to previous error

[BurntSushi]

In principle this seems fine to me, if you can get it to work. However, are there any backward compatibility/inference failure hazards? Should this get a crater run?

[clarfonthey]

@BurntSushi doesn't require crater run because From automatically implements Into, so, in principle this is just adding a From impl

[BurntSushi]

Right. I understand it shouldn't. But I've been fooled by things like this in the past. :-)

[alexcrichton]

Ah yeah unfortunately these impls are not possible due to coherence. In that case I'm going to close this.

[ollie27]

I believe it's only impl<T> From<Vec<T>> for Box<[T]> which doesn't work. The others compiled fine when I tried them.

[alexcrichton]

Ah ok! Want to send a PR with those implementations?

[ollie27]

Sure: #42227

[clarfonthey]

Thanks @ollie27 for beating me to it