This prepares the code base for when projection is interned. Place's
projection field is going to be `&List<PlaceElem<'tcx>>` so we won't be
able to pattern match against it.

Rollup of 5 pull requests

Successful merges:

 - #65544 (Added doc on keyword break)
 - #65620 (Correctly note code as Ok not error for E0573)
 - #65624 ([mir-opt] Improve SimplifyLocals pass so it can remove unused consts)
 - #65650 (use unwrap_or in lint code)
 - #65652 (Fix `canonicalize_const_var` leaking inference variables)

Failed merges:

r? @ghost

Fix `canonicalize_const_var` leaking inference variables

Fixes #61338
Fixes #61516
Fixes #62536
Fixes #64087
Fixes #64863
Fixes #65623

I added regression tests for all these issues apart from #64863, which is very similar to #61338.

r? @varkor

use unwrap_or in lint code

[mir-opt] Improve SimplifyLocals pass so it can remove unused consts

The `ConstProp` can cause many locals to be initialized to a constant
value and then never read from. `ConstProp` can also evaluate ZSTs into
constant values. Previously, many of these would be removed by other
parts of the MIR optimization pipeline. However, evaluating ZSTs
(especially `()`) into constant values defeated those parts of the
optimizer and so in a2e3ed5c, I added a
hack to `ConstProp` that skips evaluating ZSTs to avoid that regression.

This commit changes `SimplifyLocals` so that it doesn't consider writes
of const values to a local to be a use of that local. In doing so,
`SimplifyLocals` is able to remove otherwise unused locals left behind
by other optimization passes (`ConstProp` in particular).

r? @oli-obk

Correctly note code as Ok not error for E0573

Hi, this is my first pull request to the Rust project.

The fix is very small one just to fix an oversight in a comment.

Namely, [this documentation PR](https://github.com/rust-lang/rust/pull/65234) added a longer explanation for E0573. It illustrated the error using erroneous/corrected contrasting examples. But it accidentally forgot to remove `// error` from the corrected example.

Sadly, I found the error after the PR got merged. [As suggested by the original author](https://github.com/rust-lang/rust/pull/65234/files#r336518549) of the PR, I created an PR to fix this.

Part of #61137.

Added doc on keyword break

RE: #34601

bump miri

Fixes https://github.com/rust-lang/rust/issues/65529

it's type.

Check all files in `src/test` for `borrowck_graphviz_postflow`

This attribute causes DOT files to be generated in the top-level directory. It is intended to be used only temporarily and should never appear on master. This also tells git to ignore DOT files in the root or the  `mir_dump` directory, which `-Z dump-mir` uses by default.

This will prevent #65071 from occurring again. It needs to be merged after #65629, otherwise `tidy` will start failing.

r? @Mark-Simulacrum

The `ConstProp` can cause many locals to be initialized to a constant
value and then never read from. `ConstProp` can also evaluate ZSTs into
constant values. Previously, many of these would be removed by other
parts of the MIR optimization pipeline. However, evaluating ZSTs
(especially `()`) into constant values defeated those parts of the
optimizer and so in a2e3ed5c, I added a
hack to `ConstProp` that skips evaluating ZSTs to avoid that regression.

This commit changes `SimplifyLocals` so that it doesn't consider writes
of const values to a local to be a use of that local. In doing so,
`SimplifyLocals` is able to remove otherwise unused locals left behind
by other optimization passes (`ConstProp` in particular).

Rollup of 8 pull requests

Successful merges:

 - #65314 (rustdoc: forward -Z options to rustc)
 - #65592 (clarify const_prop ICE protection comment)
 - #65603 (Avoid ICE when include! is used by stdin crate)
 - #65614 (Improve error message for APIT with explicit generic arguments)
 - #65629 (Remove `borrowck_graphviz_postflow` from test)
 - #65633 (Remove leading :: from paths in doc examples)
 - #65638 (Rename the default argument 'def' to 'default')
 - #65639 (Fix parameter name in documentation)

Failed merges:

r? @ghost

Fix parameter name in documentation

Rename the default argument 'def' to 'default'

Fixes: #65492

Remove leading :: from paths in doc examples

Noted some pre-2018 path syntax in the doc examples, for example:
https://doc.rust-lang.org/std/process/fn.exit.html

```rust
fn main() {
    ::std::process::exit(match run_app() {
       Ok(_) => 0,
       ...
```

Couldn't find an existing issue on this (then again, "::" makes for an annoying thing to search for) so if there is already something fixing this and/or there's a reason to not fix it, just close this PR.

(Also fixed indentation in the `process::exit()` docs)

Remove `borrowck_graphviz_postflow` from test

Resolves #65071 (again).

Sorry. I've added a commit hook to prevent this from happening in the future.

r? @petrochenkov

Improve error message for APIT with explicit generic arguments

This is disallowed with type or const generics. cc https://github.com/rust-lang/rust/issues/61410.

Avoid ICE when include! is used by stdin crate

This should hopefully also eliminate the ICE when using `include_bytes!`, `include_str!` and `#[doc(include = "...")]` with a stdio input.

I couldn't see a clear way to write a compile-fail test using compiletest with a stdio input, so I haven't written any tests for this change.

Fixes #63900

clarify const_prop ICE protection comment

This is based on discussion at https://github.com/rust-lang/rust/pull/64890/files#r334555787.

That said, why are function arguments the only unsized locals that could remain uninitialized? Couldn't we also fail to initialize some local but still go on with const_prop, and then hit a line that takes a reference to that? Cc @wesleywiser @oli-obk ; I don't know enough about const-prop to understand why this can happen only for function arguments.

~~The PR includes https://github.com/rust-lang/rust/pull/64890; the only new commit is 05e4e6ba0d5.~~

rustdoc: forward -Z options to rustc

Currently rustdoc does not forward `-Z` options to rustc when building
test executables. This makes impossible to use rustdoc to run test
samples when crate under test is instrumented with one of sanitizers
`-Zsanitizer=...`, since the final linking step will not include
sanitizer runtime library.

Forward `-Z` options to rustc to solve the issue.

Helps with #43031.

Fixes: #65492

Rollup of 5 pull requests

Successful merges:

 - #65460 (Clean up `contains()` `insert()` chains on HashSet)
 - #65463 (Avoid unnecessary arena allocations in `expand_pattern()`.)
 - #65579 (Changed `resolve_type_vars_with_obligations` to also resolve const inference variables)
 - #65605 (Remove unreachable unit tuple compare binop codegen)
 - #65626 (trivial typo fix)

Failed merges:

r? @ghost

trivial typo fix

Remove unreachable unit tuple compare binop codegen

Closes #63906
Fixes #63551

This is based on #63906 by @luigishat, who had trouble with rebasing his PR.

Changed `resolve_type_vars_with_obligations` to also resolve const inference variables

Fixes #65380
r? @varkor

Avoid unnecessary arena allocations in `expand_pattern()`.

`expand_pattern()` has two callsites. One of them needs arena
allocation, but the other does not.

This commit moves the arena allocation out of the function. This avoids
the allocation of many 4 KiB page arena chunks that only hold a single
small allocation. It reduces the number of bytes allocated by up to 2%
for various benchmarks, albeit without only a very small improvement in
runtime.

Clean up `contains()` `insert()` chains on HashSet

They can be merged to a single `insert()` call, which may avoid double-hashing/lookup of the value.

This attribute causes DOT files to be generated in the top-level
directory. It is intended to be used only temporarily and should never
appear on master.

This will prevent #65071 from occurring again.