Matthias Krüger [Sat, 11 Dec 2021 15:02:45 +0000 (16:02 +0100)]
Rollup merge of #91617 - nnethercote:improve-List-readability, r=lcnr
Improve the readability of `List<T>`.
This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
are higher up, and incidental things are lower down, which makes
reading the code easier.
bors [Sat, 11 Dec 2021 10:37:52 +0000 (10:37 +0000)]
Auto merge of #91776 - matthiaskrgr:rollup-tlb4bw1, r=matthiaskrgr
Rollup of 6 pull requests
Successful merges:
- #91127 (Add `<*{const|mut} T>::{to|from}_bits`)
- #91310 (Add --out-dir flag for rustdoc)
- #91373 (Add needs-unwind to tests that depend on panicking)
- #91426 (Make IdFunctor::try_map_id panic-safe)
- #91515 (Add rsplit_array variants to slices and arrays)
- #91553 (socket ancillary data implementation for dragonflybsd.)
Matthias Krüger [Sat, 11 Dec 2021 07:22:31 +0000 (08:22 +0100)]
Rollup merge of #91373 - djkoloski:fuchsia_test_suite, r=Mark-Simulacrum
Add needs-unwind to tests that depend on panicking
These tests were found by running the test suite on fuchsia which compiles with `panic=abort` by default, then picking through the failures manually to locate the tests that require unwinding support.
Most of these tests are already opted-out on platforms that compile with `panic=abort` by default. This just generalizes it a bit more so that fuchsia tests can be run properly. Currently, the `needs-unwind` directive needs to be manually passed to compiletest (e.g. via `--test-args '--target-panic=abort'`). Eventually, I would like `x.py` or compiletest to determine whether the directive should be used automatically based on the target panic settings.
Matthias Krüger [Sat, 11 Dec 2021 07:22:30 +0000 (08:22 +0100)]
Rollup merge of #91310 - hi-rustin:rustin-patch-rustdoc, r=jyn514
Add --out-dir flag for rustdoc
part of https://github.com/rust-lang/rust/issues/91260
Add --out-dir flag for rustdoc and change the `-o` option to point to out-dir.
I'm not quite sure if it should be stable, also I'm not sure if this parameter priority is appropriate? Or should I just refuse to pass both parameters at the same time?
Based on the conversation in https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Adding.20methods.20as.20more.20specific.20versions.20of.20.60as.60/near/238391074
bors [Sat, 11 Dec 2021 03:52:12 +0000 (03:52 +0000)]
Auto merge of #91761 - matthiaskrgr:rollup-bjowmvz, r=matthiaskrgr
Rollup of 11 pull requests
Successful merges:
- #91668 (Remove the match on `ErrorKind::Other`)
- #91678 (Add tests fixed by #90023)
- #91679 (Move core/stream/stream/mod.rs to core/stream/stream.rs)
- #91681 (fix typo in `intrinsics::raw_eq` docs)
- #91686 (Fix `Vec::reserve_exact` documentation)
- #91697 (Delete Utf8Lossy::from_str)
- #91706 (Add unstable book entries for parts of asm that are not being stabilized)
- #91709 (Replace iterator-based set construction by *Set::From<[T; N]>)
- #91716 (Improve x.py logging and defaults a bit more)
- #91747 (Add pierwill to .mailmap)
- #91755 (Fix since attribute for const_linked_list_new feature)
bors [Sat, 11 Dec 2021 01:00:14 +0000 (01:00 +0000)]
Auto merge of #91715 - the8472:bump-rmeta-fromat-version, r=Mark-Simulacrum
Bump rmeta version to fix rustc_serialize ICE
#91407 changed the serialization format which leads to ICEs for nightly users such as #91663 and linked issues. The issue can be solved by running `cargo clean`. But bumping the metadata version should lead to the cached files being discarded, avoiding the issue entirely.
bors [Fri, 10 Dec 2021 21:59:07 +0000 (21:59 +0000)]
Auto merge of #91760 - matthiaskrgr:rollup-zcemh6j, r=matthiaskrgr
Rollup of 10 pull requests
Successful merges:
- #90407 (Document all public items in `rustc_incremental`)
- #90897 (Fix incorrect stability attributes)
- #91105 (Fix method name reference in stream documentation)
- #91325 (adjust const_eval_select documentation)
- #91470 (code-cov: generate dead functions with private/default linkage)
- #91482 (Update documentation to use `from()` to initialize `HashMap`s and `BTreeMap`s)
- #91524 (Fix Vec::extend_from_slice docs)
- #91575 (Fix ICE on format string of macro with secondary-label)
- #91625 (Remove redundant [..]s)
- #91646 (Fix documentation for `core::ready::Ready`)
Matthias Krüger [Fri, 10 Dec 2021 21:41:28 +0000 (22:41 +0100)]
Rollup merge of #91709 - juniorbassani:use-from-array-in-set-examples, r=jyn514
Replace iterator-based set construction by *Set::From<[T; N]>
This uses the array-based construction for `BtreeSet`s and `HashSet`s instead of first creating an iterator. I could also replace the `let mut a = Set::new(); a.insert(...);` fragments if desired.
Matthias Krüger [Fri, 10 Dec 2021 21:41:26 +0000 (22:41 +0100)]
Rollup merge of #91697 - dtolnay:lossyfromstr, r=Mark-Simulacrum
Delete Utf8Lossy::from_str
This whole type is marked as being for str internals only, but this constructor is never used by str internals. If you had a &str already and wanted to lossy display it or iterate its lossy utf8 chunks, you would simply not use Utf8Lossy because the whole &str is known to be one contiguous valid utf8 chunk.
If code really does need to obtain a value of type &Utf8Lossy somewhere, and has only a &str, `Utf8Lossy::from_bytes(s.as_bytes())` remains available. As currently implemented, there is no performance penalty relative to `from_str` i.e. the Utf8Lossy does not "remember" that it was constructed using `from_str` to bypass later utf8 decoding.
Matthias Krüger [Fri, 10 Dec 2021 21:40:35 +0000 (22:40 +0100)]
Rollup merge of #91575 - compiler-errors:issue-91556, r=cjgillot
Fix ICE on format string of macro with secondary-label
This generalizes the fix #86104 to also correctly skip `Span::from_inner` for the `secondary_label` of a format macro parsing error as well.
We can alternatively skip the `span_label` diagnostic call for the secondary label as well, since that label probably only makes sense when the _proper_ span is computed.
Matthias Krüger [Fri, 10 Dec 2021 21:40:33 +0000 (22:40 +0100)]
Rollup merge of #91482 - JosephTLyons:update-HashMap-and-BTreeMap-documentation, r=yaahc
Update documentation to use `from()` to initialize `HashMap`s and `BTreeMap`s
As of Rust 1.56, `HashMap` and `BTreeMap` both have associated `from()` functions. I think using these in the documentation cleans things up a bit. It allows us to remove some of the `mut`s and avoids the Initialize-Then-Modify anti-pattern.
Matthias Krüger [Fri, 10 Dec 2021 21:40:32 +0000 (22:40 +0100)]
Rollup merge of #91470 - wesleywiser:code_coverage_link_error, r=tmandry
code-cov: generate dead functions with private/default linkage
As discovered in #85461, the MSVC linker treats weak symbols slightly
differently than unix-y linkers do. This causes link.exe to fail with
LNK1227 "conflicting weak extern definition" where as other targets are
able to link successfully.
This changes the dead functions from being generated as weak/hidden to
private/default which, as the LLVM reference says:
> Global values with “private” linkage are only directly accessible by
objects in the current module. In particular, linking code into a module
with a private global value may cause the private to be renamed as
necessary to avoid collisions. Because the symbol is private to the
module, all references can be updated. This doesn’t show up in any
symbol table in the object file.
This fixes the conflicting weak symbols but doesn't address the reason
*why* we have conflicting symbols for these dead functions. The test
cases added in this commit contain a minimal repro of the fundamental
issue which is that the logic used to decide what dead code functions
should be codegen'd in the current CGU doesn't take into account that
functions can be duplicated across multiple CGUs (for instance, in the
case of `#[inline(always)]` functions).
Fixing that is likely to be a more complex change (see
https://github.com/rust-lang/rust/issues/85461#issuecomment-985005805).
Matthias Krüger [Fri, 10 Dec 2021 21:40:32 +0000 (22:40 +0100)]
Rollup merge of #91325 - RalfJung:const_eval_select, r=dtolnay
adjust const_eval_select documentation
"The Rust compiler assumes" indicates that this is language UB, but [I don't think that is a good idea](https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/topic/const_eval_select.20assumptions). This UB would be very hard to test for and looks like a way-too-big footgun. ``@oli-obk`` suggested this is meant to be more like "library UB", so I tried to adjust the docs accordingly.
I also removed all references to "referential transparency". That is a rather vague concept used to mean many different things, and I honestly have no idea what exactly is meant by it in this specific instance. But I assume ``@fee1-dead`` had in their mind a property that all `const fn` code upholds, so by demanding that the runtime code and the const-time code are *observably equivalent*, whatever that property is would also be enforced here.
Joshua Nelson [Thu, 9 Dec 2021 17:20:55 +0000 (11:20 -0600)]
Default to `doc-stage = 2` for the tools profile
This already enables `download-rustc`, so it's quick to build rustdoc,
and this makes it less confusing when changes to rustdoc aren't reflected in the docs.
Note that this uses 2 and not 1 because `download-rustc` only affects stage 2 runs.
This info is occasionally useful when debugging bootstrap itself, but not very useful for figuring
out why a config option was ignored or command wasn't run. Demote it to `-vv` logging so that `-v`
is more useful.
The 8472 [Thu, 9 Dec 2021 17:00:36 +0000 (18:00 +0100)]
Bump rmeta version to fix rustc_serialize ICE
#91407 changed the serialization format which leads to ICEs for nightly users such as #91663 and linked issue.
Bumping the metadata version should lead to the cached files being discarded instead.
bors [Thu, 9 Dec 2021 15:01:42 +0000 (15:01 +0000)]
Auto merge of #85157 - the8472:drain-drop-in-place, r=Mark-Simulacrum
replace vec::Drain drop loops with drop_in_place
The `Drain::drop` implementation came up in https://github.com/rust-lang/rust/pull/82185#issuecomment-789584796 as potentially interfering with other optimization work due its widespread use somewhere in `println!`
bors [Thu, 9 Dec 2021 07:08:32 +0000 (07:08 +0000)]
Auto merge of #91692 - matthiaskrgr:rollup-u7dvh0n, r=matthiaskrgr
Rollup of 6 pull requests
Successful merges:
- #87599 (Implement concat_bytes!)
- #89999 (Update std::env::temp_dir to use GetTempPath2 on Windows when available.)
- #90796 (Remove the reg_thumb register class for asm! on ARM)
- #91042 (Use Vec extend instead of repeated pushes on several places)
- #91634 (Do not attempt to suggest help for overly malformed struct/function call)
- #91685 (Install llvm tools to sysroot when assembling local toolchain)
This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
are higher up, and incidental things are lower down, which makes
reading the code easier.
Matthias Krüger [Thu, 9 Dec 2021 04:08:34 +0000 (05:08 +0100)]
Rollup merge of #91685 - Aaron1011:install-llvm-tools, r=Mark-Simulacrum
Install llvm tools to sysroot when assembling local toolchain
Some projects (e.g. the `bootimage` crate) may require the
user to install the `llvm-tools-preview` rustup component.
However, this cannot be easily done with a locally built toolchain.
To allow a local toolchain to be used a drop-in replacement for
a normal rustup toolchain in more cases, this PR copies the built
LLVM tools to the sysoot. From the perspective a tool looking
at the sysroot, this is equivalent to installing `llvm-tools-preview`.
Matthias Krüger [Thu, 9 Dec 2021 04:08:33 +0000 (05:08 +0100)]
Rollup merge of #91042 - Kobzol:vec-extend-cleanup, r=nagisa
Use Vec extend instead of repeated pushes on several places
Inspired by https://github.com/rust-lang/rust/pull/90813, I tried to use a simple regex (`for .*in.*\{\n.*push\(.*\);\n\s+}`) to search for more places that would use `Vec::push` in a loop and replace them with `Vec::extend`.
These probably won't have as much perf. impact as the original PR (if any), but it would probably be better to do a perf run to see if there are not any regressions.
Matthias Krüger [Thu, 9 Dec 2021 04:08:31 +0000 (05:08 +0100)]
Rollup merge of #89999 - talagrand:GetTempPath2, r=m-ou-se
Update std::env::temp_dir to use GetTempPath2 on Windows when available.
As a security measure, Windows 11 introduces a new temporary directory API, GetTempPath2.
When the calling process is running as SYSTEM, a separate temporary directory
will be returned inaccessible to non-SYSTEM processes. For non-SYSTEM processes
the behavior will be the same as before.
This can help mitigate against attacks such as this one:
https://medium.com/csis-techblog/cve-2020-1088-yet-another-arbitrary-delete-eop-a00b97d8c3e2
Compatibility risk: Software which relies on temporary files to communicate between SYSTEM and non-SYSTEM
processes may be affected by this change. In many cases, such patterns may be vulnerable to the very
attacks the new API was introduced to harden against.
I'm unclear on the Rust project's tolerance for such change-of-behavior in the standard library. If anything,
this PR is meant to raise awareness of the issue and hopefully start the conversation.
How tested: Taking the example code from the documentation and running it through psexec (from SysInternals) on
Win10 and Win11.
On Win10:
C:\test>psexec -s C:\test\main.exe
<...>
Temporary directory: C:\WINDOWS\TEMP\
On Win11:
C:\test>psexec -s C:\test\main.exe
<...>
Temporary directory: C:\Windows\SystemTemp\
Matthias Krüger [Thu, 9 Dec 2021 04:08:30 +0000 (05:08 +0100)]
Rollup merge of #87599 - Smittyvb:concat_bytes, r=Mark-Simulacrum
Implement concat_bytes!
This implements the unstable `concat_bytes!` macro, which has tracking issue #87555. It can be used like:
```rust
#![feature(concat_bytes)]
fn main() {
assert_eq!(concat_bytes!(), &[]);
assert_eq!(concat_bytes!(b'A', b"BC", [68, b'E', 70]), b"ABCDEF");
}
```
If strings or characters are used where byte strings or byte characters are required, it suggests adding a `b` prefix. If a number is used outside of an array it suggests arrayifying it. If a boolean is used it suggests replacing it with the numeric value of that number. Doubly nested arrays of bytes are disallowed.
Notice that `return` and `yield` already follow the same approach as this PR of printing the space *before* each additional piece following the keyword, rather than *after* each thing.
Matthias Krüger [Thu, 9 Dec 2021 04:02:19 +0000 (05:02 +0100)]
Rollup merge of #91042 - Kobzol:vec-extend-cleanup, r=nagisa
Use Vec extend instead of repeated pushes on several places
Inspired by https://github.com/rust-lang/rust/pull/90813, I tried to use a simple regex (`for .*in.*\{\n.*push\(.*\);\n\s+}`) to search for more places that would use `Vec::push` in a loop and replace them with `Vec::extend`.
These probably won't have as much perf. impact as the original PR (if any), but it would probably be better to do a perf run to see if there are not any regressions.
bors [Thu, 9 Dec 2021 00:55:49 +0000 (00:55 +0000)]
Auto merge of #91677 - matthiaskrgr:rollup-yiczced, r=matthiaskrgr
Rollup of 5 pull requests
Successful merges:
- #91245 (suggest casting between i/u32 and char)
- #91337 (Add a suggestion if `macro_rules` is misspelled)
- #91534 (Make rustdoc headings black, and markdown blue)
- #91637 (Add test for packed drops in generators)
- #91667 (Fix indent of itemTypes in search.js)
Failed merges:
- #91568 (Pretty print break and continue without redundant space)
Aaron Hill [Thu, 9 Dec 2021 00:35:53 +0000 (18:35 -0600)]
Install llvm tools to sysroot when assembling local toolchain
Some projects (e.g. the `bootimage` crate) may require the
user to install the `llvm-tools-preview` rustup component.
However, this cannot be easily done with a locally built toolchain.
To allow a local toolchain to be used a drop-in replacement for
a normal rustup toolchain in more cases, this PR copies the built
LLVM tools to the sysoot. From the perspective a tool looking
at the sysroot, this is equivalent to installing `llvm-tools-preview`.
(Note: we may want to make rustdoc headings and markdown headings the same color -- #90245 -- but we would want to do that intentionally; this is fixing up a change that did so accidentally)
Matthias Krüger [Wed, 8 Dec 2021 22:18:03 +0000 (23:18 +0100)]
Rollup merge of #91245 - cameron1024:suggest-i32-u32-char-cast, r=nagisa
suggest casting between i/u32 and char
As discussed in https://github.com/rust-lang/rust/issues/91063 , this adds a suggestion for converting between i32/u32 <-> char with `as`, and a short explanation for why this is safe
bors [Wed, 8 Dec 2021 18:45:03 +0000 (18:45 +0000)]
Auto merge of #91665 - matthiaskrgr:rollup-o3wnkam, r=matthiaskrgr
Rollup of 7 pull requests
Successful merges:
- #90709 (Only shown relevant type params in E0283 label)
- #91551 (Allow for failure of subst_normalize_erasing_regions in const_eval)
- #91570 (Evaluate inline const pat early and report error if too generic)
- #91571 (Remove unneeded access to pretty printer's `s` field in favor of deref)
- #91610 (Link to rustdoc_json_types docs instead of rustdoc-json RFC)
- #91619 (Update cargo)
- #91630 (Add missing whitespace before disabled HTML attribute)
Matthias Krüger [Wed, 8 Dec 2021 15:08:11 +0000 (16:08 +0100)]
Rollup merge of #91619 - ehuss:update-cargo, r=ehuss
Update cargo
8 commits in 294967c53f0c70d598fc54ca189313c86c576ea7..40dc281755137ee804bc9b3b08e782773b726e44
2021-11-29 19:04:22 +0000 to 2021-12-06 21:54:44 +0000
- Unify the description of quiet flag (rust-lang/cargo#10168)
- Stabilize future-incompat-report (rust-lang/cargo#10165)
- Support abbreviating `--release` as `-r` (rust-lang/cargo#10133)
- doc: nudge towards simple version requirements (rust-lang/cargo#10158)
- Upgrade clap to 2.34.0 (rust-lang/cargo#10164)
- Treat EOPNOTSUPP the same as ENOTSUP when ignoring failed flock calls. (rust-lang/cargo#10157)
- Add note about RUSTFLAGS removal from build scripts. (rust-lang/cargo#10141)
- Make clippy happy (rust-lang/cargo#10139)
Matthias Krüger [Wed, 8 Dec 2021 15:08:10 +0000 (16:08 +0100)]
Rollup merge of #91610 - aDotInTheVoid:patch-2, r=GuillaumeGomez
Link to rustdoc_json_types docs instead of rustdoc-json RFC
The JSON format has had [many changes](https://github.com/rust-lang/rust/commits/master/src/rustdoc-json-types) since the RFC, so the rustdoc output is the only up to date reference
Matthias Krüger [Wed, 8 Dec 2021 15:08:09 +0000 (16:08 +0100)]
Rollup merge of #91571 - dtolnay:printerderef, r=Mark-Simulacrum
Remove unneeded access to pretty printer's `s` field in favor of deref
I found it taxing in some of my recent PRs touching the pretty printer to maintain consistency with the surrounding code, since the current code is all over the place about whether it uses `self.s.…()` or `self.…()` for invoking methods of `rustc_ast_pretty::pp::Printer`.
This PR standardizes on `self.…()` — relying on the `Deref` and `DerefMut` impls introduced by [#62532](https://github.com/rust-lang/rust/pull/62532/commits/cab453250a3ceae5cf0cf7eac836c03b37e4ca8e).
Using associated types that cannot be normalized previously resulted in an ICE. We now allow for normalization failure and return a "TooGeneric" error in that case.
Matthias Krüger [Wed, 8 Dec 2021 15:08:06 +0000 (16:08 +0100)]
Rollup merge of #90709 - estebank:erase-known-type-params, r=nagisa
Only shown relevant type params in E0283 label
When we point at a binding to suggest giving it a type, erase all the
type for ADTs that have been resolved, leaving only the ones that could
not be inferred. For small shallow types this is not a problem, but for
big nested types with lots of params, this can otherwise cause a lot of
unnecessary visual output.
bors [Wed, 8 Dec 2021 14:58:48 +0000 (14:58 +0000)]
Auto merge of #91604 - nikic:section-flags, r=nagisa
Use object crate for .rustc metadata generation
We already use the object crate for generating uncompressed .rmeta
metadata object files. This switches the generation of compressed
.rustc object files to use the object crate as well. These have
slightly different requirements in that .rmeta should be completely
excluded from any final compilation artifacts, while .rustc should
be part of shared objects, but not loaded into memory.
The primary motivation for this change is #90326: In LLVM 14, the
current way of setting section flags (and in particular, preventing
the setting of SHF_ALLOC) will no longer work. There are other ways
we could work around this, but switching to the object crate seems
like the most elegant, as we already use it for .rmeta, and as it
makes this independent of the codegen backend. In particular, we
don't need separate handling in codegen_llvm and codegen_gcc.
codegen_cranelift should be able to reuse the implementation as
well, though I have omitted that here, as it is not based on
codegen_ssa.
This change mostly extracts the existing code for .rmeta handling
to allow using it for .rustc as well, and adjusts the codegen
infrastructure to handle the metadata object file separately: We
no longer create a backend-specific module for it, and directly
produce the compiled module instead.
This does not `fix` #90326 by itself yet, as .llvmbc will need to be
handled separately.
bors [Wed, 8 Dec 2021 11:22:02 +0000 (11:22 +0000)]
Auto merge of #91656 - matthiaskrgr:rollup-lk96y6d, r=matthiaskrgr
Rollup of 7 pull requests
Successful merges:
- #83744 (Deprecate crate_type and crate_name nested inside #![cfg_attr])
- #90550 (Update certificates in some Ubuntu 16 images.)
- #91272 (Print a suggestion when comparing references to primitive types in `const fn`)
- #91467 (Emphasise that an OsStr[ing] is not necessarily a platform string)
- #91531 (Do not add `;` to expected tokens list when it's wrong)
- #91577 (Address some FIXMEs left over from #91475)
- #91638 (Remove `in_band_lifetimes` from `rustc_mir_transform`)
Matthias Krüger [Wed, 8 Dec 2021 10:09:01 +0000 (11:09 +0100)]
Rollup merge of #91638 - scottmcm:less-inband-2-of-28, r=petrochenkov
Remove `in_band_lifetimes` from `rustc_mir_transform`
Like #91580, this was inspired by the conversation in #44524 about possibly removing the feature from the compiler. This crate is a heavy `'tcx` user, so is a nice case study.
r? ``@petrochenkov``
Three interesting ones:
This one had the `'tcx` declared on the function, despite the trait taking a `'tcx`:
```diff
-impl Visitor<'_> for UsedLocals {
+impl<'tcx> Visitor<'tcx> for UsedLocals {
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
```
This one use in-band for one, and underscore for the other:
```diff
-pub fn remove_dead_blocks(tcx: TyCtxt<'tcx>, body: &mut Body<'_>) {
+pub fn remove_dead_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
```
Matthias Krüger [Wed, 8 Dec 2021 10:09:00 +0000 (11:09 +0100)]
Rollup merge of #91577 - ecstatic-morse:mir-pass-manager-cleanup, r=oli-obk
Address some FIXMEs left over from #91475
This shouldn't change behavior, only clarify what we're currently doing. I filed #91576 to see if the treatment of generator drop shims is intentional.
Matthias Krüger [Wed, 8 Dec 2021 10:08:58 +0000 (11:08 +0100)]
Rollup merge of #91467 - ChrisDenton:confusing-os-string, r=Mark-Simulacrum
Emphasise that an OsStr[ing] is not necessarily a platform string
Fixes #53261
Since that issue was filed, #56141 added a further clarification to the `OsString` docs. However the ffi docs may still leave the impression that an `OsStr` is in the platform native form. This PR aims to further emphasise that an `OsStr` is not necessarily a platform string.