Fix std::fs::copy on WASI target
Previously `std::fs::copy` on wasm32-wasi would reuse code from the `sys_common` module and would successfully copy contents of the file just to fail right before closing it.
This was happening because `sys_common::copy` tries to copy permissions of the file, but permissions are not a thing in WASI (at least yet) and `set_permissions` is implemented as an unconditional runtime error.
This change instead adds a custom working implementation of `std::fs::copy` (like Rust already has on some other targets) that doesn't try to call `set_permissions` and is essentially a thin wrapper around `std::io::copy`.
Fixes#68560.
Added From<Vec<NonZeroU8>> for CString
Added a `From<Vec<NonZeroU8>>` `impl` for `CString`
# Rationale
- `CString::from_vec_unchecked` is a subtle function, that makes `unsafe` code harder to audit when the generated `Vec`'s creation is non-trivial. This `impl` allows to write safer `unsafe` code thanks to the very explicit semantics of the `Vec<NonZeroU8>` type.
- One such situation is when trying to `.read()` a `CString`, see issue #59229.
- this lead to a PR: #59314, that was closed for being too specific / narrow (it only targetted being able to `.read()` a `CString`, when this pattern could have been generalized).
- the issue suggested another route, based on `From<Vec<NonZeroU8>>`, which is indeed a less general and more concise code pattern.
- quoting @shnatsel:
- > For me the main thing about making this safe is simplifying auditing - people have spent like an hour looking at just this one unsafe block in libflate because it's not clear what exactly is unchecked, so you have to look it up when auditing anyway. This has distracted us from much more serious memory safety issues the library had.
Having this trivial impl in stdlib would turn this into safe code with compiler more or less guaranteeing that it's fine, and save anyone auditing the code a whole lot of time.
Previously `std::fs::copy` on wasm32-wasi would reuse code from the `sys_common` module and would successfully copy contents of the file just to fail right before closing it.
This was happening because `sys_common::copy` tries to copy permissions of the file, but permissions are not a thing in WASI (at least yet) and `set_permissions` is implemented as an unconditional runtime error.
This change instead adds a custom working implementation of `std::fs::copy` (like Rust already has on some other targets) that doesn't try to call `set_permissions` and is essentially a thin wrapper around `std::io::copy`.
Fixes#68560.
Add a method to query the capacity of a BufWriter and BufReader
Besides the obvious of retrieving the parameter used to construct the writer, this method allows consumers to control the number of `flush` calls during write operations. For `BufReader` it gives an upper bound on the returned buffer in `fill_buf` which might influence the allocation behaviour of a consumer.
Updated tracking issue number
Added safeguards for transmute_vec potentially being factored out elsewhere
Clarified comment about avoiding mem::forget
Removed unneeded unstable guard
Added back a stability annotation for CI
Minor documentation improvements
Thanks to @Centril's code review
Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>
Improved layout checks, type annotations and removed unaccurate comment
Removed unnecessary check on array layout
Adapt the stability annotation to the new 1.41 milestone
Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>
Simplify the implementation.
Use `Vec::into_raw_parts` instead of a manual implementation of
`Vec::transmute`.
If `Vec::into_raw_parts` uses `NonNull` instead, then the code here
will need to be adjusted to take it into account (issue #65816)
Reduce the whitespace of safety comments
Step stage0 to bootstrap from 1.42
This also includes a commit which fixes the rustfmt downloading logic to redownload when the rustfmt channel changes, and bumps rustfmt to a more recent version.
