f64 methods have been stable since rust 1.0, but f32 never got stabilised.

I suggest backporting this to beta as well (needs changing stablilisation version then).

r? @aturon

Fixes https://github.com/rust-lang/rfcs/issues/1438

f64 methods have been stable since rust 1.0, but f32 never got stabilised.

When looking in the documentation I often scan the examples the first thing I do. In these 3 cases it's not obvious which direction the operation happens by adding this comment it makes it more obvious.

r? @steveklabnik

CC #30642

r? @Gankro

Are trait impls still insta-stable? Considering that this design has been around for a long time on `String` and `OsString` it probably doesn't matter much...

The `From` impl is a bit strange to me. It's stolen from `OsString` but I'm not really sure about it... `String` just impls `From<&str>` instead, would that make more sense?

CC #30642

- Successful merges: #30365, #30565, #30590, #30630
- Failed merges:

Previously, all references to closure arguments went to the argument before the one they should (e.g. to `arg1` when it was supposed to go to `arg2`). This was because the MIR builder did not account for the implicit arguments that come before the explicit arguments, and closures have one implicit argument - the struct containing the captures.

This is my test code and a diff of the MIR generated for the closure:

```rust
let a = 2i32;
let _f = |b: i32| -> i32 { a + b }:
```

```diff
--- old	2015-12-29 23:16:32.027926372 -0600
+++ new	2015-12-29 23:16:42.975400757 -0600
@@ -1,22 +1,22 @@
 fn(arg0: &[closure@closure-args.rs:8:14: 8:39 a:&i32], arg1: i32) -> i32 {
     let var0: i32; // b
     let tmp0: ();
     let tmp1: i32;
     let tmp2: i32;

     bb0: {
-        var0 = arg0;
+        var0 = arg1;
         tmp1 = (*(*arg0).0);
         tmp2 = var0;
         ReturnPointer = Add(tmp1, tmp2);
         goto -> bb1;
     }

     bb1: {
         return;
     }

     bb2: {
         diverge;
     }
 }
```

(If you're wondering where this text MIR output comes from, it's from another branch of mine waiting on https://github.com/rust-lang/rust/pull/30602 to get merged.)

This moves back (essentially reverts #30265) into MIR-specific translation code, but keeps the
funcition split out, since it is expected to eventually become recursive.

Fixes https://github.com/rust-lang/rust/issues/29572

cc @oli-obk

This PR changes the `emit_opaque` and `read_opaque` methods in the RBML library to use a space-efficient binary encoder that does not emit any tags and uses the LEB128 variable-length integer format for all numbers it emits.

The space savings are nice, albeit a bit underwhelming, especially for dynamic libraries where metadata is already compressed.

| RLIBs        |  NEW   |   OLD     |
|--------------|--------|-----------|
|libstd        | 8.8 MB |  10.5 MB  |
|libcore       |15.6 MB |   19.7 MB |
|libcollections| 3.7 MB |    4.8 MB |
|librustc      |34.0 MB |   37.8 MB |
|libsyntax     |28.3 MB |   32.1 MB |

| SOs           |     NEW   |    OLD |
|---------------|-----------|--------|
| libstd        |  4.8 MB   | 5.1 MB |
| librustc      |  8.6 MB   | 9.2 MB |
| libsyntax     |  7.8 MB   | 8.4 MB |

At least this should make up for the size increase caused recently by also storing MIR in crate metadata.

Can this be a breaking change for anyone?
cc @rust-lang/compiler

Since `darwin` is really `apple-darwin`, the valgrind-rpass tests were not actually being run with valgrind on mac before. Also, the `HOST` check was completely wrong.

r? @alexcrichton

This hairy conditional doesn't need to be so. It _does_ need to be a
thin pointer, otherwise, it will fail to compile, so let's pull that out
into a temporary for future readers of the source.

/cc @nrc @SimonSapin @Gankro @durka , who brought this up on IRC

The previous version using `PartialOrd::le` was broken since it passed `T` arguments where `&T` was expected.

It makes sense to use primitive comparisons since range patterns can only be used with chars and numeric types.

r? @EddyB

The current help message is too much about "normal" macros to be used
as general message. Keep it for normal macros, and add custom help and
error messages for macro definitions.

I think that should pretty much conclude all of https://github.com/rust-lang/rust/issues/29576.

RESTRICTION_STMT_EXPR restriction to allow subsequent expressions to
contain braces.

https://github.com/rust-lang/rust/issues/28777

Fixes #30521 and #30627 by adding new snapshots
edunham uploaded the snapshots.

This adds a constructor for a Weak that can never be upgraded. These are
mostly useless, but for example are required when deserializing.

This hairy conditional doesn't need to be so. It _does_ need to be a
thin pointer, otherwise, it will fail to compile, so let's pull that out
into a temporary for future readers of the source.

Also, after a discussion with @pnkfelix and @gankro, we don't need these
null checks anymore, as zero-on-drop has been gone for a while now.

The previous version using `PartialOrd::le` was broken since it passed `T`
arguments where `&T` was expected.

It makes sense to use primitive comparisons since range patterns can only be
used with chars and numeric types.

- Successful merges: #30373, #30502, #30511, #30546, #30556, #30620
- Failed merges:

The current help message is too much about "normal" macros to be used
as general message. Keep it for normal macros, and add custom help and
error messages for macro definitions.