When encountering a method call for an ADT that doesn't have any
implementation of it, we search for traits that could be implemented
that do have that method. Filter out private non-local traits that would
not be able to be implemented.

This doesn't account for public traits that are in a private scope, but
works as a first approximation and is a more correct behavior than the
current one.

When the compiler driver panics it attempts to show a hint about using
`RUST_BACKTRACE`. However, the logic is currently reversed to the hint
is only shown if `RUST_BACKTRACE` is *already* set:

```shell
> RUST_BACKTRACE=1 rustc /dev/null --crate-type proc-macro
error: internal compiler error: unexpected panic
...
note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'attempt to subtract with overflow', librustc_errors/emitter.rs:287:49
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

> RUST_BACKTRACE=0 rustc /dev/null --crate-type proc-macro
error: internal compiler error: unexpected panic
...
thread 'rustc' panicked at 'attempt to subtract with overflow', librustc_errors/emitter.rs:287:49
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```

As the `panic` itself already has a working `RUST_BACKTRACE` hint just
remove the broken duplicate hint entirely.

Now that the Rust codebase depends on cc 1.0.4, there is no longer any
need to specify a compiler for CloudABI manually. Cargo will
automatically call into the right compiler executable.

As discussed in rust-lang#47699 the logic for determining if an expression needs
parenthesis when suggesting an `.into()` cast is incorrect. Two broken
examples from nightly are:

```
error[E0308]: mismatched types
 --> main.rs:4:10
  |
4 |     test(foo as i8);
  |          ^^^^^^^^^ expected i32, found i8
help: you can cast an `i8` to `i32`, which will sign-extend the source value
  |
4 |     test(foo as i8.into());
  |
```

```
error[E0308]: mismatched types
 --> main.rs:4:10
  |
4 |     test(*foo);
  |          ^^^^ expected i32, found i8
help: you can cast an `i8` to `i32`, which will sign-extend the source value
  |
4 |     test(*foo.into());
  |
```

As suggested by @petrochenkov switch the precedence check to
PREC_POSTFIX. This catches both `as` and unary operators. Fixes rust-lang#47699.

Just a routine update

…etrochenkov

On missing method do not suggest private traits

When encountering a method call for an ADT that doesn't have any
implementation of it, we search for traits that could be implemented
that do have that method. Filter out private non-local traits that would
not be able to be implemented.

This doesn't account for public traits that are in a private scope, but
works as a first approximation and is a more correct behavior than the
current one.

Fix rust-lang#45781.

…nikomatsakis

NLL test for mutating &mut references

As mentioned in rust-lang#46361.

cc @nikomatsakis?

…hint, r=estebank

Remove broken redundant backtrace hint

When the compiler driver panics it attempts to show a hint about using `RUST_BACKTRACE`. However, the logic is currently reversed to the hint is only shown if `RUST_BACKTRACE` is **already**   set:

```shell
> RUST_BACKTRACE=1 rustc /dev/null --crate-type proc-macro
error: internal compiler error: unexpected panic
...
note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'attempt to subtract with overflow', librustc_errors/emitter.rs:287:49
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

> RUST_BACKTRACE=0 rustc /dev/null --crate-type proc-macro
error: internal compiler error: unexpected panic
...
thread 'rustc' panicked at 'attempt to subtract with overflow', librustc_errors/emitter.rs:287:49
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```

As the `panic` itself already has a working `RUST_BACKTRACE` hint just remove the broken duplicate hint entirely.

…ruppe

Point at unknown lang item attribute

Remove workarounds for cc 1.0.3.

Now that the Rust codebase depends on cc 1.0.4, there is no longer any
need to specify a compiler for CloudABI manually. Cargo will
automatically call into the right compiler executable.

…nce, r=petrochenkov

Fix into() cast paren check precedence

As discussed in rust-lang#47699 the logic for determining if an expression needs parenthesis when suggesting an `.into()` cast is incorrect. Two broken examples from nightly are:

```
error[E0308]: mismatched types
 --> main.rs:4:10
  |
4 |     test(foo as i8);
  |          ^^^^^^^^^ expected i32, found i8
help: you can cast an `i8` to `i32`, which will sign-extend the source value
  |
4 |     test(foo as i8.into());
  |
```

```
error[E0308]: mismatched types
 --> main.rs:4:10
  |
4 |     test(*foo);
  |          ^^^^ expected i32, found i8
help: you can cast an `i8` to `i32`, which will sign-extend the source value
  |
4 |     test(*foo.into());
  |
```

As suggested by @petrochenkov switch the precedence check to `PREC_POSTFIX`. This catches both `as` and unary operators. Fixes rust-lang#47699.

r? @petrochenkov

…veklabnik

fix for documentation error issue 47716

Fix rust-lang#47716

…r=QuietMisdreavus

Fix experimental text display on default theme

r? @QuietMisdreavus

…s-span, r=petrochenkov

Fix spans in unused import lint for nested groups

This fixes an inconsistency for empty nested groups, and adds a test for all the possible cases of the lint.

```
warning: unused imports: `*`, `Foo`, `baz::{}`, `foobar::*`
  --> test.rs:16:11
   |
16 | use foo::{Foo, bar::{baz::{}, foobar::*}, *};
   |           ^^^        ^^^^^^^  ^^^^^^^^^   ^
   |
   = note: #[warn(unused_imports)] on by default

warning: unused import: `*`
  --> test.rs:17:24
   |
17 | use foo::bar::baz::{*, *};
   |                        ^

warning: unused import: `use foo::{};`
  --> test.rs:18:1
   |
18 | use foo::{};
   | ^^^^^^^^^^^^
```

cc rust-lang#44494

Update Cargo submodule to master

Just a routine update