Otherwise, changing the current working directory can mess up runtime linking.

Disallow methods from traits that are not in scope

This PR only allows a trait method to be used if the trait is in scope (fixes #31379).
This is a [breaking-change]. For example, the following would break:
```rust
mod foo {
    pub trait T { fn f(&self) {} }
    impl T for () {}
}

mod bar { pub use foo::T; }

fn main() {
    pub use bar::*;
    struct T; // This shadows the trait `T`,
    ().f() // making this an error.
}
```
r? @nikomatsakis

Scopes in mir

This PR adds scopes to MIR. There is a tree of scopes (each represented by a `ScopeId`). Every statement, variable, and terminator now has an associated scope and span.  It also adds a `-Z dump-mir` switch one can use to conveniently examine the MIR as optimizations proceed.

The intention is two-fold. First, to support MIR debug-info. This PR does not attempt to modify trans to make use of the scope information, however.

Second, in a more temporary capacity, to support the goal of moving regionck and borowck into the MIR. To that end, the PR also constructs a "scope auxiliary" table storing the extent of each span (this is kept separate from the main MIR, since it contains node-ids) and the dom/post-dom of the region in the graph where the scope occurs. When we move to non-lexical lifetimes, I expect this auxiliary information to be discarded, but that is still some ways in the future (requires, at minimum, an RFC, and there are some thorny details to work out -- though I've got an in-progress draft).

Right now, I'm just dropping this auxiliary information after it is constructed. I was debating for some time whether to add some sort of sanity tests, but decided to just open this PR instead, because I couldn't figure out what such a test would look like (and we don't have independent tests for this today beyond the regionck and borrowck tests).

I'd prefer not to store the auxiliary data into any kind of "per-fn" map. Rather, I'd prefer that we do regionck/borrowck/whatever-else immediately after construction -- that is, we build the MIR for fn X and immediately thereafter do extended correctness checking on it. This will reduce peak memory usage and also ensure that the auxiliary data doesn't exist once optimizations begin. It also clarifies the transition point where static checks are complete and MIR can be more freely optimized.

cc @rust-lang/compiler @nagisa

Add core::ops::Range*::contains() as per rust-lang/rust#32311

Remove `ErasedRegions` from substs

This commit removes the `ErasedRegions` enum from `Substs`. Instead, in trans, we just generate a vector of `ReStatic` of suitable length. The goal is both general cleanup and to help pave the way for a glorious future where erasure is used in type check.

r? @EddyB

One concern: might be nice to do some profiling. Not sure the best way to do that. Perhaps I'll investigate running nrc's test suite locally.

This hack has long since outlived its usefulness; the transition to
trans passing around full substitutions is basically done. Instead of
`ErasedRegions`, just supply substitutions with a suitable number of
`'static` entries, and invoke `erase_regions` when needed (the latter of
which we already do).

It no longer reads from `ast_ty_to_ty_cache`, which was very wrong. It
also correctly handles higher-ranked regions.

Rollup of 6 pull requests

- Successful merges: #32276, #32416, #32452, #32459, #32462, #32464
- Failed merges:

Improve some Option code example

Part of #29366.

r? @steveklabnik

Docs: some tiny corrections

TNT->`tnt`
firecracker->`firecracker`

Include source text in JSON errors

Add code examples for libstd/time

Fixes #29379.

r? @steveklabnik

Add doc example to clone trait

Fixes #29346.

r? @steveklabnik

doc: Stdin is not writable

We now visit more things (e.g., types) and also follow a deliberate
style designed to reduce omissions.

TNT->`tnt`
firecracker->`firecracker`

Make warnings of renamed and removed lints themselves lints

This adds the `renamed_and_removed_lints` warning, defaulting
to the warning level.

Fixes #31141

Signed-off-by: NNODA, Kai <nodakai@gmail.com>

while I'm at it, remove the "extra caching" that I was doing for no good
reason except laziness. Basically before I was caching at each scope in
the chain, but there's not really a reason to do that, since the cached
entry point at level N is always equal to the last cached exit point
from level N-1.

This adds the `renamed_and_removed_lints` warning, defaulting
to the warning level.

Fixes #31141

add naked function tracking issue # to feature gate definition

also, when exiting a scope, assign the final goto terminator with the
target scope's id