This stabilizes the `Path::try_exists()` method which returns
`Result<bool, io::Error>` instead of `bool` allowing handling of errors
unrelated to the file not existing. (e.g permission errors)

Along with the stabilization it also:

* Warns that the `exists()` method is error-prone and suggests to use
  the newly stabilized one.
* Suggests it instead of `metadata()` to handle errors.
* Mentions TOCTOU bugs to avoid false assumption that `try_exists()` is
  completely safe fixed version of `exists()`.
* Renames the feature of still-unstable `std::fs::try_exists()` to
  `fs_try_exists` to avoid name conflict.

The tracking issue rust-lang#83186 remains open to track `fs_try_exists`.

… path

This ensures that changes to target json files will force a
recompilation. And more importantly that moving the files doesn't force
a recompilation.

This is useful for combinators. I didn't add `clone` since you can already
use `Clone::clone` in its place; copy has no such corresponding function.

Add `core::mem::copy` to complement `core::mem::drop`.

This is useful for combinators. I didn't add `clone` since you can already
use `Clone::clone` in its place; copy has no such corresponding function.

…r=dtolnay

Stabilize `Path::try_exists()` and improve doc

This stabilizes the `Path::try_exists()` method which returns
`Result<bool, io::Error>` instead of `bool` allowing handling of errors
unrelated to the file not existing. (e.g permission errors)

Along with the stabilization it also:

* Warns that the `exists()` method is error-prone and suggests to use
  the newly stabilized one.
* Suggests it instead of `metadata()` to handle errors.
* Mentions TOCTOU bugs to avoid false assumption that `try_exists()` is
  completely safe fixed version of `exists()`.
* Renames the feature of still-unstable `std::fs::try_exists()` to
  `fs_try_exists` to avoid name conflict.

The tracking issue rust-lang#83186 remains open to track `fs_try_exists`.

…agisa

Make debug_triple depend on target json file content rather than file path

This ensures that changes to target json files will force a recompilation. And more importantly that moving the files doesn't force a recompilation.

This should fix Rust-for-Linux/linux#792 (cc ``@ojeda)``

…lan-DPC

Fix typos in `IntoFuture` docs