Change filesearch::get_or_default_sysroot() to check if sysroot is found
using env::args().next() if rustc in argv[0] is a symlink; otherwise, or
if it is not found, use env::current_exe() to imply sysroot. This makes
the rustc binary able to locate Rust libraries in systems using
content-addressable storage (CAS).

This makes it clear that it's an implementation detail of `display_fn`
and shouldn't be used elsewhere, and it enforces in the compiler that no
one else can use it.

We used to ignore `forbid(group)` scenarios completely. This changed
in rust-lang#78864, but that led to a number of regressions (rust-lang#80988, rust-lang#81218).

This PR introduces a future compatibility warning for the case where
a group is forbidden but then an individual lint within that group
is allowed. We now issue a FCW when we see the "allow", but permit
it to take effect.

Per a comment on rust-lang#70516 this changes `eq_ignore_ascii_case` to take the generic parameter `S: AsRef<OsStr>` by value instead of by reference.

This is technically a breaking change to an unstable method. I think the only way it would break is if you called this method with an explicit type parameter, ie `my_os_str.eq_ignore_ascii_case::<str>("foo")` becomes `my_os_str.eq_ignore_ascii_case::<&str>("foo")`.

Besides that, I believe it is overall more flexible since it can now take an owned `OsString` for example.

If this change should be made in some other PR (like rust-lang#80193) then please just close this.

This comes up a lot when bootstrapping.

This extends the `panic_fmt` lint to warn for all cases where the first
argument cannot be interpreted as a format string, as will happen in
Rust 2021.

It suggests to add `"{}", ` to format the message as a string. In the
case of `std::panic!()`, it also suggests the recently stabilized
`std::panic::panic_any()` function as an alternative.

It renames the lint to `non_fmt_panic` to match the lint naming
guidelines.

…gisa

Fix rustc sysroot in systems using CAS

Change filesearch::get_or_default_sysroot() to check if sysroot is found using env::args().next() if rustc in argv[0] is a symlink; otherwise, or if it is not found, use env::current_exe() to imply sysroot. This makes the rustc binary able to locate Rust libraries in systems using content-addressable storage (CAS).

Rename Iterator::fold_first to reduce and stabilize it

This stabilizes `#![feature(iterator_fold_self)]`.

The name for this function (originally `fold_first`) was still an open question, but the discussion on [the tracking issue](rust-lang#68125) seems to have converged to `reduce`.

rustdoc-json: Fix has_body

Previously, `has_body` was always true. Now propagate the type of the method to set it correctly. Relies on rust-lang#81287, that will need to be merged first.

tidy: Run tidy style against markdown files.

This adds tidy checks for markdown files.  I think it is useful to have some style enforcement (for the same reasons the style is enforced on other files).  I think it is worthwhile to avoid `ignore` on rust examples since having broken code in documentation is frustrating.  Avoiding trailing whitespace is good because it has semantic meaning in markdown, which I think should be avoided.

…ell, r=jyn514

rustdoc: Move `display_fn` struct inside `display_fn`

This makes it clear that it's an implementation detail of `display_fn`
and shouldn't be used elsewhere, and it enforces in the compiler that no
one else can use it.

r? `@GuillaumeGomez`

…lint, r=pnkfelix

introduce future-compatibility warning for forbidden lint groups

We used to ignore `forbid(group)` scenarios completely. This changed in rust-lang#78864, but that led to a number of regressions (rust-lang#80988, rust-lang#81218).

This PR introduces a future compatibility warning for the case where a group is forbidden but then an individual lint within that group is allowed. We now issue a FCW when we see the "allow", but permit it to take effect.

r? ```@Mark-Simulacrum```

…1995

Add lint for `panic!(123)` which is not accepted in Rust 2021.

This extends the `panic_fmt` lint to warn for all cases where the first argument cannot be interpreted as a format string, as will happen in Rust 2021.

It suggests to add `"{}",` to format the message as a string. In the case of `std::panic!()`, it also suggests the recently stabilized
`std::panic::panic_any()` function as an alternative.

It renames the lint to `non_fmt_panic` to match the lint naming guidelines.

![image](https://user-images.githubusercontent.com/783247/106520928-675ea680-64d5-11eb-81f7-d8fa48b93a0b.png)

This is part of rust-lang#80162.

r? `@estebank`

Add more information to the error code for 'crate not found'

This comes up a lot when bootstrapping.

…, r=oli-obk

Add additional bitset benchmarks

Add additional benchmarks for operations in bitset, I realize that it was a bit lacking when I intended to optimize it earlier, so I was hoping to put some in so I can verify my work later.

OsStr eq_ignore_ascii_case takes arg by value

Per a comment on rust-lang#70516 this changes `eq_ignore_ascii_case` to take the generic parameter `S: AsRef<OsStr>` by value instead of by reference.

This is technically a breaking change to an unstable method. I think the only way it would break is if you called this method with an explicit type parameter, ie `my_os_str.eq_ignore_ascii_case::<str>("foo")` becomes `my_os_str.eq_ignore_ascii_case::<&str>("foo")`.

Besides that, I believe it is overall more flexible since it can now take an owned `OsString` for example.

If this change should be made in some other PR (like rust-lang#80193) then please just close this.

Move test to be with the others

No functional changes. I just created this test in the wrong place in a past PR. All of the other or-pattern tests are in the `or-patterns` directory.

…mulacrum

Revert stabilizing integer::BITS.

We agreed in the libs meeting just now to revert stablization, since the [breakage](rust-lang#81654) is significant throughout the ecosystem, through `lexical-core`.

cc rust-lang#76904

Fixes rust-lang#81654