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Pull recent changes from https://github.com/rust-lang/rust via Josh.
Upstream ref: 425a9c0a0e365c0b8c6cfd00c2ded83a73bed9a0
Filtered ref: 26b9fd24259f4fc5fd7634a99dd6dda2821fb2d0
This merge was created using https://github.com/rust-lang/josh-sync.
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This updates the rust-version file to 425a9c0a0e365c0b8c6cfd00c2ded83a73bed9a0.
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This is intended to be used for Linux kernel RETPOLINE builds.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
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Switch to only using aarch64 runners (implying we are now
cross-compiling) and stop running tests. In the future, we could
enable (some?) tests via Rosetta 2.
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Implement autodiff using intrinsics
This PR aims to move autodiff logic to `autodiff` intrinsic. Allowing us to delete a great part of our frontend code and overall, simplify the compilation pipeline of autodiff functions.
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Rust documentation, use `rustc-dev-guide` :3
reviving rust-lang/rust#145385 but on my own fork this time
r? ``@BoxyUwU``
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Improve tracing in bootstrap
I was annoyed that bootstrap had like 5 separate ways of debugging/tracing/profiling, and it was hard for me to understand how are individual steps executed. This PR tries to unify severla things behind `BOOTSTRAP_TRACING`, and improve tracing/profiling in general:
- All generated tracing outputs are now stored in a single directory to make it easier to examine them, plus bootstrap prepares a `latest` symlink to the latest generated tracing output directory for convenience.
- All executed spans are now logged automatically (without requiring usage of `#[tracing::instrument]`).
- A custom span/event formatter was implemented, to provide domain-specific output (like location of executed commands or spans) and hopefully also to reduce visual clutter.
- `tracing_forest` was removed. While it did some useful postprocessing, it didn't expose enough information for making the dynamic step spans work.
- You can now explicitly log steps (`STEP=info`) and/or commands (`COMMAND=info`), to have more granular control over what gets logged.
- `print-step-timings` also show when a step starts its execution (not just when it ends it), so that when some step fails in CI, we can actually see what step it was (before we would only see the end of the previous step).
- The rustc-dev-guide page on debugging/profiling bootstrap was updated.
There are still some things that work outside of tracing (`print-step-timings` and `dump-bootstrap-shims`), but I think that for now this improvement is good enough.
I removed the `> step`, `< step` verbose output, because I found it unusable, as verbose bootstrap output also enables verbose Cargo output, and then you simply drown in too much data, and because I think that the new tracing system makes it obsolete (although it does require recompilation with the `tracing` feature). If you want to keep it, happy to revert 690c781475acb890f33d928186bdaea9ef179330. And the information about cached steps is now also shown in the Graphviz step dependency graph.
We can modify the tracing output however we want, as we now implement it ourselves. Notably, we could also show exit logs for step spans, currently I only show enter spans. Maybe creating indents for each executed nested command is also not needed. Happy to hear feedback!
Some further improvements could be to print step durations, if we decide to also log step exit events. We could also try to enable tracing in CI logs, but it might be too verbose.
Best reviewed commit-by-commit.
r? ``@jieyouxu``
CC ``@Shourya742``
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Improve `--remap-path-prefix` documentation
This PR improves the `--remap-path-prefix` documentation by:
- moving it into it's own page
- adding a small example
- mentioning that the remapping is best effort[^1]
- mentioning `link.exe`/PDB issues[^2]
- mentioning the path separator issue (textual replacement)
r? ``@wesleywiser``
[^1]: [#t-compiler > link.exe leaking paths in Windows PDB @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/link.2Eexe.20leaking.20paths.20in.20Windows.20PDB/near/523343774)
[^2]: [#t-compiler > link.exe leaking paths in Windows PDB @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/link.2Eexe.20leaking.20paths.20in.20Windows.20PDB/near/523331762)
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Co-Authored-By: Weihang Lo <me@weihanglo.tw>
Co-Authored-By: Wesley Wiser <wwiser@gmail.com>
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Add another example for escaped `#` character in doctest in rustdoc book
Fixes rust-lang/rust#118027.
We don't plan to add a way to not escape the first `#`, so at least we add a more complete example in the rustdoc book with a macro making use of that.
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r=davidtwco
Add aarch64_be-unknown-none-softfloat target
This adds a new target for bare-metal big endian ARM64 without FPU. We want to use this in [the Hermit unikernel](https://github.com/hermit-os/kernel) because big endian ARM64 is the most accessible big endian architecture for us and it can be supported with our existing aarch64 code. I have compiled our kernel and bootloader with this target and they work as expected in QEMU.
Regarding the [tier 3 target policy](https://doc.rust-lang.org/rustc/target-tier-policy.html#tier-3-target-policy):
> - A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
The maintainer(s) (currently just me) are listed in the markdown document that documents the target.
> - Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
> - Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
> - If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
The target name is consistent with the existing `aarch64-unknown-none-softfloat` target and the existing big endian aarch64 targets like `aarch64_be-unknown-linux-gnu`.
> - Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
> - The target must not introduce license incompatibilities.
> - Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
> - The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
> - Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
> - "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
There are no licensing issues and any toolchain that can compile for `aarch64-unknown-none-softfloat` can also compile for `aarch64_be-unknown-none-softfloat` (well, at least GCC and LLVM). No proprietary components are required.
> - Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
> - This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
Ack.
> - Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
This target does not implement std and is equivalent to `aarch64-unknown-none-softfloat` in all these regards.
> - The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
Ack, that is part of the markdown document.
> - Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via ```@)``` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
> - Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
Ack.
> - Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
> - In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
This doesn't break any existing targets.
> - Tier 3 targets must be able to produce assembly using at least one of rustc's supported backends from any host target. (Having support in a fork of the backend is not sufficient, it must be upstream.)
The LLVM backend works.
> - If a tier 3 target stops meeting these requirements, or the target maintainers no longer have interest or time, or the target shows no signs of activity and has not built for some time, or removing the target would improve the quality of the Rust codebase, we may post a PR to remove it; any such PR will be CCed to the target maintainers (and potentially other people who have previously worked on the target), to check potential interest in improving the situation.
Ack.
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Fix parallel rustc not being reproducible due to unstable sorts of items
Currently, A tuple `(DefId, SymbolName)` is used to determine the order of items in the final binary. However `DefId` is expected as non-deterministic, which leads to some not reproducible issues under parallel compilation. (See https://github.com/rust-lang/rust/issues/140425#issuecomment-3111802148)
Theoretically, we don't need the sorting because the order of these items is already deterministic.
However, codegen tests reply on the same order of items between in binary and source.
So here we added a new option `codegen-source-order` to indicate whether sorting based on the order in source. For codegen tests, items are sorted according to the order in the source code, whereas in the normal path, no sorting is performed.
Specially, for codegen tests, in preparation for parallel compilation potentially being enabled by default in the future, we use `Span` replacing `DefId` to make the order deterministic.
This PR is purposed to fix rust-lang/rust#140425, but seemly works on rust-lang/rust#140413 too.
This behavior hasn't added into any test until we have a test suit for the parallel frontend. (See https://github.com/rust-lang/rust/pull/143953)
Related discussion: [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/187679-t-compiler.2Fparallel-rustc/topic/Async.20closures.20not.20reproducible.28.23140425.29) https://github.com/rust-lang/rust/pull/144576
Update rust-lang/rust#113349
r? `@oli-obk`
cc `@lqd` `@cramertj` `@matthiaskrgr` `@Zoxc` `@SparrowLii` `@bjorn3` `@cjgillot` `@joshtriplett`
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Deprecate RUST_TEST_* env variables
Like with rust-lang/rust#139224, this is a documentation-only deprecation for now. Over time, we can
- warn and then remove on use of unstable environment variables
- warn on use of stable environment variables (no plan to remove due to compatibility)
Longer term, we expect test runners, like `cargo test`, to provide the necessary mechanisms for environmental or persistent configuration (e.g. using cargo config which supports `.cargo/config.toml` as well as environment variables).
This would include:
- `RUST_TEST_THREADS`
- `RUST_TEST_NOCAPTURE`
- `RUST_TEST_SHUFFLE` (unstable)
- `RUST_TEST_SHUFFLE_SEED` (unstable)
The primary outcomes for this change are
- Reducing the scope of what is expected for custom test harnesses to implement
- Reduce the mechanisms that test runners, like `cargo test`, are expected to track when they are being bypassed to protect against negative interactions, e.g. `RUST_TEST_NOCAPTURE=1` when json output is being read.
For testing-devex FCP, see rust-lang/testing-devex-team#10
Fixes rust-lang/testing-devex-team#10
History
-------
At each step, I could not find evidence of design discussions on whether to support CLI, env, or both. The first env variable seems to come from the fact that it was being forked out of an existing env variable that had a much wider scope.
At best, this seems like a way to offer a more persistent configuration for these flags but environment variables hidden away in libtest is a bit clunky and this seems like the wrong layer to handle this problem.
**Originally:** `RUST_THREADS` was respected by the Rust runtime and libextra/test got this for free
**2013:** rust-lang/rust#7335 suggested splitting `RUST_TEST_TASKS` out of `RUST_THREADS`. In that issue and the implementation (rust-lang/rust#8823).
**2014:** rust-lang/rust#13374 ask for support to disable capturing of stdout/stderr. `--nocapture` and `RUST_TEST_NOCAPTURE` were added together.
**2015:** rust-lang/rust#23525 renamed `RUST_TEST_TASKS` to `RUST_TEST_THREADS`
**2016:** rust-lang/rust#25636 asked to configure `RUST_TEST_THREADS` via `--test-threads` which was implemented in rust-lang/rust#35414
**2021:** rust-lang/rust#85440 asked for test randomization which was implemented in rust-lang/rust#89082, adding `--shuffle` / RUST_TEST_SHUFFLE` and `--shuffle-seed SEED` / `RUST_TEST_SHUFFLE_SEED`
Potentially relevant issues
---------------------------
- rust-lang/rust#74845
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Consolidate stage directories and group logs in bootstrap
My post-stage-0-redesign bootstrap fixes aren't done yet, but I think that enough steps have been migrated to the new system that it makes sense to actually modify the directories on disk, and what gets printed when bootstrap runs, so that it actually corresponds to the new system. Before, the printed stages didn't always make sense.
This PR:
- Fixes the numbering of `stageN` directories in the build directory. It was not corresponding to the correct stages before; notice that I did not modify `bootstrap/README.md`, as it was essentially describing what happens after this PR (first commit).
- Unifies all steps that output a build group to use the `Builder::msg` method. It's probably not the final stage, and some of the test steps might not be fully accurate yet, because I didn't fix test step numbering yet, but I think that it's a clear improvement from before, and now that everything uses the same method, we can easily make changes across the board, to ensure that it stays unified (second commit).
r? `@jieyouxu`
try-job: dist-x86_64-msvc
try-job: dist-x86_64-linux
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Update books
## rust-lang/reference
6 commits in 1be151c051a082b542548c62cafbcb055fa8944f..59b8af811886313577615c2cf0e045f01faed88b
2025-08-10 18:21:53 UTC to 2025-08-08 01:00:04 UTC
- Add LoongArch32 to inline-assembly documentation (rust-lang/reference#1942)
- Update `no_builtins` to use the attribute template (rust-lang/reference#1909)
- Update `global_allocator` to use the attribute template (rust-lang/reference#1919)
- Update `windows_subsystem` to use the attribute template (rust-lang/reference#1920)
- Remove note on accepted invalid `should_panic` syntax (rust-lang/reference#1955)
- specify relative drop order of pattern bindings (rust-lang/reference#1953)
## rust-lang/rust-by-example
1 commits in bd1279cdc9865bfff605e741fb76a0b2f07314a7..adc1f3b9012ad3255eea2054ca30596a953d053d
2025-08-08 12:02:24 UTC to 2025-08-08 12:02:24 UTC
- Update Chinese translations in `zh.po` (rust-lang/rust-by-example#1950)
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Support using #[unstable_feature_bound] on trait
This is needed to unblock https://github.com/rust-lang/rust/pull/145095
r? ```````@BoxyUwU```````
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Co-authored-by: zachs18 <8355914+zachs18@users.noreply.github.com>
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This is more in-line with what Apple's tooling expects, and allows us to
better support custom compiler drivers (such as certain Homebrew and
Nixpkgs compilers) that prefer their own `-isysroot` flag.
Effectively, we now invoke the compiler driver as-if it was invoked as
`xcrun -sdk $sdk_name $tool`.
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This is a documentation-only deprecation for now.
Over time, we can
- warn and then remove on use of unstable environment variables
- warn on use of stable environment variables (no plan to remove due to
compatibility)
Longer term, we expect test runners, like `cargo test`, to provide the
necessary mechanisms for environmental or persistent configuration (e.g.
using cargo config which supports `.cargo/config.toml` as well as
environment variables).
This would include:
- `RUST_TEST_THREADS`
- `RUST_TEST_NOCAPTURE`
- `RUST_TEST_SHUFFLE` (unstable)
- `RUST_TEST_SHUFFLE_SEED` (unstable)
The primary outcomes for this change are
- Reducing the scope of what is expected for custom test harnesses to
implement
- Reduce the mechanisms that test runners, like `cargo test`, are
expected to track when they are being bypassed to protect against
negative interactions, e.g. `RUST_TEST_NOCAPTURE=1` when json output
is being read.
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see https://github.com/rust-lang/rust/pull/145253 for reference.
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Also, remove redundant word
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r=ChrisDenton
Stabilize `duration_constructors_lite` feature
This closes [tracking issue](https://github.com/rust-lang/rust/issues/140881) and stabilises `Duration::from_hours` and `Duration::from_mins` while not touching a `duration_constructors` feature from the related [tracking issue (2)](https://github.com/rust-lang/rust/issues/120301)
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Stabilize loongarch32 inline asm
r? ````````@Amanieu````````
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unstable-book: Add stubs for environment variables; document some of the important ones
This uses a very hacky regex that will probably miss some variables. But having some docs seems better than none at all.
In particular, this documents the following env vars explicitly (cc ````````@madsmtm```````` ````````@flba-eb```````` - do the docs for SDKROOT and QNX_TARGET look right?):
- COLORTERM
- QNX_TARGET
- SDKROOT
- TERM
and generates stubs for the following env vars:
- RUST_BACKTRACE
- RUSTC_BLESS
- RUSTC_BREAK_ON_ICE
- RUSTC_CTFE_BACKTRACE
- RUSTC_FORCE_RUSTC_VERSION
- RUSTC_GRAPHVIZ_FONT
- RUSTC_ICE
- RUSTC_LOG
- RUSTC_RETRY_LINKER_ON_SEGFAULT
- RUSTC_TRANSLATION_NO_DEBUG_ASSERT
- RUST_DEP_GRAPH_FILTER
- RUST_DEP_GRAPH
- RUST_FORBID_DEP_GRAPH_EDGE
- RUST_MIN_STACK
- RUST_TARGET_PATH
- UNSTABLE_RUSTDOC_TEST_LINE
- UNSTABLE_RUSTDOC_TEST_PATH
rendered: 
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Co-authored-by: Florian Bartels <108917393+flba-eb@users.noreply.github.com>
Co-authored-by: Mads Marquart <mads@marquart.dk>
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The official Discord server is no longer active (cannot be posted to).
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Add minimal `armv7a-vex-v5` tier three target
This PR adds minimal, `no_std` support for the VEX V5 Brain, a robotics microcontroller used in educational contexts. In comparison to rust-lang/rust#131530, which aimed to add this same target, these changes are limited in scope to the compiler.
## Tier 3 Target Policy Compliance
> A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
Lewis McClelland (`@lewisfm),` `@Tropix126,` Gavin Niederman (`@Gavin-Niederman),` and Max Niederman (`@max-niederman)` will be the designated maintainers for `armv7a-vex-v5` support.
> Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
`armv7a-vex-v5` follows the cpu-vendor-model convention used by most tier three targets. For example: `armv76k-nintendo-3ds` or `armv7k-apple-watchos`.
> Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
> If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
This target name is not confusing.
> Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
It's using open source tools only.
> The target must not introduce license incompatibilities.
>
> Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
Understood.
> The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
There are no new dependencies/features required in the current state of this target. Porting the standard library will likely require depending on the crate `vex-sdk` which is MIT-licensed and contains bindings to the VEX SDK runtime (which is included in VEXos).
> Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
>
> "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
Although the VEX V5 Brain and its SDK are proprietary, this target does not link to any proprietary binaries or libraries, and is based solely on publicly available information about the VEX SDK.
> Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
>
> This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
I understand.
> Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
This initial PR only contains a compiler target definition to teach the `cc` crate about this target. Porting the standard library is the next step for this target.
> The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
This target is documented in `src/doc/rustc/src/platform-support/armv7a-vex-v5.md`.
> Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via `@)` to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
>
> Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
I understand and assent.
> Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
>
> In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
I understand and assent.
> Tier 3 targets must be able to produce assembly using at least one of rustc's supported backends from any host target. (Having support in a fork of the backend is not sufficient, it must be upstream.)
`armv7a-vex-v5` has nearly identical codegen to `armv7a-none-eabihf`, so this is not an issue.
> If a tier 3 target stops meeting these requirements, or the target maintainers no longer have interest or time, or the target shows no signs of activity and has not built for some time, or removing the target would improve the quality of the Rust codebase, we may post a PR to remove it; any such PR will be CCed to the target maintainers (and potentially other people who have previously worked on the target), to check potential interest in improving the situation.
I understand.
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coverage: Remove all unstable support for MC/DC instrumentation
Preliminary support for a partial implementation of “Modified Condition/Decision Coverage” instrumentation was added behind the unstable flag `-Zcoverage-options=mcdc` in 2024. These are the most substantial PRs involved:
- rust-lang/rust#123409
- rust-lang/rust#126733
At the time, I accepted these PRs with relatively modest scrutiny, because I did not want to stand in the way of independent work on MC/DC instrumentation. My hope was that ongoing work by interested contributors would lead to the code becoming clearer and more maintainable over time.
---
However, that MC/DC code has proven itself to be a major burden on overall maintenance of coverage instrumentation, and a major obstacle to other planned improvements, such as internal changes needed for proper support of macro expansion regions.
I have also become reluctant to accept any further MC/DC-related changes that would increase this burden.
That tension has resulted in an unhappy impasse. On one hand, the present MC/DC implementation is not yet complete, and shows little sign of being complete at an acceptable level of code quality in the foreseeable future. On the other hand, the continued existence of this partial MC/DC implementation is imposing serious maintenance burdens on every other aspect of coverage instrumentation, and is preventing some of the very improvements that would make it easier to accept expanded MC/DC support in the future.
While I know this will be disappointing to some, I think the healthy way forward is accept that I made the wrong call in accepting the current implementation, and to remove it entirely from the compiler.
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> A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
Lewis McClelland (lewisfm), Tropix126, Gavin Niederman (Gavin-Niederman), and Max Niederman (max-niederman) will be the designated maintainers for `armv7a-vex-v5` support.
> Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
`armv7a-vex-v5` follows the cpu-vendor-model convention used by most tier three targets. For example: `armv76k-nintendo-3ds` or `armv7k-apple-watchos`.
> Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
> If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
This target name is not confusing.
> Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
It's using open source tools only.
> The target must not introduce license incompatibilities.
>
> Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
Understood.
> The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
There are no new dependencies/features required in the current state of this target. Porting the standard library will likely require depending on the crate `vex-sdk` which is MIT-licensed and contains bindings to the VEX SDK runtime (which is included in VEXos).
> Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
>
> "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
Although the VEX V5 Brain and its SDK are proprietary, this target does not link to any proprietary binaries or libraries, and is based solely on publicly available information about the VEX SDK.
> Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
>
> This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
I understand.
> Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
This initial PR only contains a compiler target definition to teach the `cc` crate about this target. Porting the standard library is the next step for this target.
> The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
This target is documented in `src/doc/rustc/src/platform-support/armv7a-vex-v5.md`.
> Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via @) to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
>
> Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
I understand and assent.
> Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
>
> In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
I understand and assent.
> Tier 3 targets must be able to produce assembly using at least one of rustc's supported backends from any host target. (Having support in a fork of the backend is not sufficient, it must be upstream.)
`armv7a-vex-v5` has nearly identical codegen to `armv7a-none-eabihf`, so this is not an issue.
> If a tier 3 target stops meeting these requirements, or the target maintainers no longer have interest or time, or the target shows no signs of activity and has not built for some time, or removing the target would improve the quality of the Rust codebase, we may post a PR to remove it; any such PR will be CCed to the target maintainers (and potentially other people who have previously worked on the target), to check potential interest in improving the situation.
I understand.
Co-authored-by: Max Niederman <max@maxniederman.com>
Co-authored-by: Tropical <42101043+Tropix126@users.noreply.github.com>
Co-authored-by: Gavin Niederman <gavinniederman@gmail.com>
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rustc-dev-guide subtree update
Subtree update of `rustc-dev-guide` to https://github.com/rust-lang/rustc-dev-guide/commit/1beca6333e2de8df2d002613c7c8fce55a1a1257.
Created using https://github.com/rust-lang/josh-sync.
r? `@ghost`
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Update books
## rust-lang/book
5 commits in b2d1a0821e12a676b496d61891b8e3d374a8e832..3e9dc46aa563ca0c53ec826c41b05f10c5915925
2025-08-02 01:33:29 UTC to 2025-07-14 21:23:38 UTC
- Appendix B and Appendix D from tech review (rust-lang/book#4466)
- Chapter 21 from tech review (rust-lang/book#4464)
- Chapter 20 from tech review (rust-lang/book#4460)
- Chapter 19 from tech review (rust-lang/book#4446)
- Chapter 18 from tech review (rust-lang/book#4445)
## rust-lang/reference
12 commits in 1f45bd41fa6c17b7c048ed6bfe5f168c4311206a..1be151c051a082b542548c62cafbcb055fa8944f
2025-08-05 19:51:40 UTC to 2025-07-14 19:49:01 UTC
- Fix build output directory in README (rust-lang/reference#1950)
- Update `link_name` to use the attribute template (rust-lang/reference#1896)
- Update `no_link` to use the attribute template (rust-lang/reference#1898)
- Update `proc_macro_derive` to use the attribute template (rust-lang/reference#1888)
- Update `automatically_derived` to use the attribute template (rust-lang/reference#1884)
- Update `derive` to use the attribute template (rust-lang/reference#1883)
- Fix and clarify CR LF normalization and CR in string literals (rust-lang/reference#1944)
- glossary.md: tweak description of "dispatch" (rust-lang/reference#1938)
- add missing id, r[asm.operand-type.supported-operands.const] (rust-lang/reference#1939)
- &str and &[u8] have the same layout (rust-lang/reference#1848)
- Rename and rewrite the "question mark operator" (rust-lang/reference#1931)
- Change "allocated object" to "allocation". (rust-lang/reference#1930)
## rust-lang/rust-by-example
3 commits in e386be5f44af711854207c11fdd61bb576270b04..bd1279cdc9865bfff605e741fb76a0b2f07314a7
2025-08-04 13:41:04 UTC to 2025-08-02 15:41:59 UTC
- Improve the activity instructions in `print_display` (rust-lang/rust-by-example#1948)
- Minor fixes (whitespace, typo, i32->u32) (rust-lang/rust-by-example#1947)
- Document drawbacks of alternatives to match binding (rust-lang/rust-by-example#1946)
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add nvptx_target_feature
Tracking issue: #141468 (nvptx), which is part of #44839 (catch-all arches)
The feature gate is `#![feature(nvptx_target_feature)]`
This exposes the target features `sm_20` through `sm_120a` [as defined](https://github.com/llvm/llvm-project/blob/llvmorg-20.1.1/llvm/lib/Target/NVPTX/NVPTX.td#L59-L85) by LLVM.
Cc: ``````@gonzalobg``````
``````@rustbot`````` label +O-NVPTX +A-target-feature
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