Initial implementation of unsafe binder types

[compiler-errors]

I've written up some motivation about unsafe binders here: https://hackmd.io/@compiler-errors/HkXwoBPaR

Specifically, I'd like to provide a coherent way to represent lifetimes in structs which are unnameable and can't be plugged by 'static. This has been toyed around with in the past, such as 'unsafe lifetimes¹, but the document above calls out some questions in that design and proposes a different solution via "unsafe binder types". Making these their own distinct type solves a lot of those problems, and while users still need to be careful with these types by using unsafe {} when interconverting them, they're far more self-contained.

r? @ghost

I'll be opening a lang team experiment for this before I put this up for actual review. I'm mostly putting this here so we can reference it.

Tracking:

• Tracking issue for unsafe binder types #130516

Footnotes

1. https://internals.rust-lang.org/t/rfc-basic-unsafe-lifetime/16873 ↩

[bors]

☔ The latest upstream changes (presumably #130724) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

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#16 2.893 Building wheels for collected packages: reuse
#16 2.894   Building wheel for reuse (pyproject.toml): started
#16 3.138   Building wheel for reuse (pyproject.toml): finished with status 'done'
#16 3.139   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132715 sha256=dfa09868353292d98f811d3efdb0d54d07389e808efc71d68e3b93c514bf8bec
#16 3.140   Stored in directory: /tmp/pip-ephem-wheel-cache-jvcljmyz/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#16 3.142 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#16 3.530 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#16 3.530 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#16 DONE 3.6s
---
    Checking toml_edit v0.19.15
    Checking semver v1.0.23
    Checking cargo_metadata v0.18.1
    Checking toml v0.7.8
error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a method that returns `Result`
     |
     |
792  |     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
     |     ------------------------------------------------------------------------------------- this function returns a `Result`
...
1022 |                     shape.offset_left(result.len())?
     |                                                    ^ use `.ok_or(...)?` to provide an error compatible with `std::result::Result<std::string::String, RewriteError>`
     |
     = help: the trait `FromResidual<std::option::Option<Infallible>>` is not implemented for `std::result::Result<std::string::String, RewriteError>`
     = help: the trait `FromResidual<std::result::Result<Infallible, E>>` is implemented for `std::result::Result<T, F>`

error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a method that returns `Result`
     |
     |
792  |     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
     |     ------------------------------------------------------------------------------------- this function returns a `Result`
...
1024 |                     shape.visual_indent(result.len()).sub_width(result.len())?
     |                                                                              ^ use `.ok_or(...)?` to provide an error compatible with `std::result::Result<std::string::String, RewriteError>`
     |
     = help: the trait `FromResidual<std::option::Option<Infallible>>` is not implemented for `std::result::Result<std::string::String, RewriteError>`
     = help: the trait `FromResidual<std::result::Result<Infallible, E>>` is implemented for `std::result::Result<T, F>`

error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a method that returns `Result`
     |
     |
792  |     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
     |     ------------------------------------------------------------------------------------- this function returns a `Result`
...
1027 |                 let rewrite = binder.inner_ty.rewrite(context, inner_ty_shape)?;
     |                                                                               ^ use `.ok_or(...)?` to provide an error compatible with `std::result::Result<std::string::String, RewriteError>`
     |
     = help: the trait `FromResidual<std::option::Option<Infallible>>` is not implemented for `std::result::Result<std::string::String, RewriteError>`
     = help: the trait `FromResidual<std::result::Result<Infallible, E>>` is implemented for `std::result::Result<T, F>`
error[E0308]: mismatched types
    --> src/tools/rustfmt/src/types.rs:1029:17
     |
     |
792  |     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
     |                                                                             ------------- expected `std::result::Result<std::string::String, RewriteError>` because of return type
1029 |                 Some(result)
1029 |                 Some(result)
     |                 ^^^^^^^^^^^^ expected `Result<String, RewriteError>`, found `Option<String>`
     = note: expected enum `std::result::Result<std::string::String, RewriteError>`
                found enum `std::option::Option<std::string::String>`

Some errors have detailed explanations: E0277, E0308.

[bors]

☔ The latest upstream changes (presumably #127117) made this pull request unmergeable. Please resolve the merge conflicts.