bors d9c3f0d690 Auto merge of #84039 - jyn514:uplift-atomic-ordering, r=wesleywiser
Uplift the invalid_atomic_ordering lint from clippy to rustc

This is mostly just a rebase of https://github.com/rust-lang/rust/pull/79654; I've copy/pasted the text from that PR below.

r? `@lcnr` since you reviewed the last one, but feel free to reassign.

---

This is an implementation of https://github.com/rust-lang/compiler-team/issues/390.

As mentioned, in general this turns an unconditional runtime panic into a (compile time) lint failure. It has no false positives, and the only false negatives I'm aware of are if `Ordering` isn't specified directly and is comes from an argument/constant/whatever.

As a result of it having no false positives, and the alternative always being strictly wrong, it's on as deny by default. This seems right.

In the [zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/233931-t-compiler.2Fmajor-changes/topic/Uplift.20the.20.60invalid_atomic_ordering.60.20lint.20from.20clippy/near/218483957) `@joshtriplett` suggested that lang team should FCP this before landing it. Perhaps libs team cares too?

---

Some notes on the code for reviewers / others below

## Changes from clippy

The code is changed from [the implementation in clippy](68cf94f6a6/clippy_lints/src/atomic_ordering.rs) in the following ways:

1. Uses `Symbols` and `rustc_diagnostic_item`s instead of string literals.
    - It's possible I should have just invoked Symbol::intern for some of these instead? Seems better to use symbol, but it did require adding several.
2. The functions are moved to static methods inside the lint struct, as a way to namespace them.
    - There's a lot of other code in that file — which I picked as the location for this lint because `@jyn514` told me that seemed reasonable.
3. Supports unstable AtomicU128/AtomicI128.
    - I did this because it was almost easier to support them than not — not supporting them would have (ideally) required finding a way not to give them a `rustc_diagnostic_item`, which would have complicated an already big macro.
    - These don't have tests since I wasn't sure if/how I should make tests conditional on whether or not the target has the atomic... This is to a certain extent an issue of 64bit atomics too, but 128-bit atomics are much less common. Regardless, the existing tests should be *more* than thorough enough here.
4. Minor changes like:
    - grammar tweaks ("loads cannot have `Release` **and** `AcqRel` ordering" => "loads cannot have `Release` **or** `AcqRel` ordering")
    - function renames (`match_ordering_def_path` => `matches_ordering_def_path`),
    - avoiding clippy-specific helper methods that don't exist in rustc_lint and didn't seem worth adding for this case (for example `cx.struct_span_lint` vs clippy's `span_lint_and_help` helper).

## Potential issues

(This is just about the code in this PR, not conceptual issues with the lint or anything)

1. I'm not sure if I should have used a diagnostic item for `Ordering` and its variants (I couldn't figure out how really, so if I should do this some pointers would be appreciated).
    - It seems possible that failing to do this might possibly mean there are more cases this lint would miss, but I don't really know how `match_def_path` works and if it has any pitfalls like that, so maybe not.

2. I *think* I deprecated the lint in clippy (CC `@flip1995` who asked to be notified about clippy changes in the future in [this comment](https://github.com/rust-lang/rust/pull/75671#issuecomment-718731659)) but I'm not sure if I need to do anything else there.
    - I'm kind of hoping CI will catch if I missed anything, since `x.py test src/tools/clippy` fails with a lot of errors with and without my changes (and is probably a nonsense command regardless). Running `cargo test` from src/tools/clippy also fails with unrelated errors that seem like refactorings that didnt update clippy? So, honestly no clue.

3. I wasn't sure if the description/example I gave good. Hopefully it is. The example is less thorough than the one from clippy here: https://rust-lang.github.io/rust-clippy/master/index.html#invalid_atomic_ordering. Let me know if/how I should change it if it needs changing.

4. It pulls in the `if_chain` crate. This crate was already used in clippy, and seems like it's used elsewhere in rustc, but I'm willing to rewrite it to not use this if needed (I'd prefer not to, all things being equal).
2021-08-16 06:36:13 +00:00
2020-02-12 09:34:25 +01:00
2021-02-02 18:13:18 +01:00
2020-02-12 09:34:25 +01:00

Clippy

Clippy Test License: MIT OR Apache-2.0

A collection of lints to catch common mistakes and improve your Rust code.

There are over 450 lints included in this crate!

Lints are divided into categories, each with a default lint level. You can choose how much Clippy is supposed to annoy help you by changing the lint level by category.

Category Description Default level
clippy::all all lints that are on by default (correctness, suspicious, style, complexity, perf) warn/deny
clippy::correctness code that is outright wrong or useless deny
clippy::suspicious code that is most likely wrong or useless warn
clippy::style code that should be written in a more idiomatic way warn
clippy::complexity code that does something simple but in a complex way warn
clippy::perf code that can be written to run faster warn
clippy::pedantic lints which are rather strict or might have false positives allow
clippy::nursery new lints that are still under development allow
clippy::cargo lints for the cargo manifest allow

More to come, please file an issue if you have ideas!

The lint list also contains "restriction lints", which are for things which are usually not considered "bad", but may be useful to turn on in specific cases. These should be used very selectively, if at all.

Table of contents:

Usage

Below are instructions on how to use Clippy as a subcommand, compiled from source or in Travis CI.

As a cargo subcommand (cargo clippy)

One way to use Clippy is by installing Clippy through rustup as a cargo subcommand.

Step 1: Install rustup

You can install rustup on supported platforms. This will help us install Clippy and its dependencies.

If you already have rustup installed, update to ensure you have the latest rustup and compiler:

rustup update

Step 2: Install Clippy

Once you have rustup and the latest stable release (at least Rust 1.29) installed, run the following command:

rustup component add clippy

If it says that it can't find the clippy component, please run rustup self update.

Step 3: Run Clippy

Now you can run Clippy by invoking the following command:

cargo clippy

Automatically applying Clippy suggestions

Clippy can automatically apply some lint suggestions, just like the compiler.

cargo clippy --fix

Workspaces

All the usual workspace options should work with Clippy. For example the following command will run Clippy on the example crate:

cargo clippy -p example

As with cargo check, this includes dependencies that are members of the workspace, like path dependencies. If you want to run Clippy only on the given crate, use the --no-deps option like this:

cargo clippy -p example -- --no-deps

As a rustc replacement (clippy-driver)

Clippy can also be used in projects that do not use cargo. To do so, you will need to replace your rustc compilation commands with clippy-driver. For example, if your project runs:

rustc --edition 2018 -Cpanic=abort foo.rs

Then, to enable Clippy, you will need to call:

clippy-driver --edition 2018 -Cpanic=abort foo.rs

Note that rustc will still run, i.e. it will still emit the output files it normally does.

Travis CI

You can add Clippy to Travis CI in the same way you use it locally:

language: rust
rust:
  - stable
  - beta
before_script:
  - rustup component add clippy
script:
  - cargo clippy
  # if you want the build job to fail when encountering warnings, use
  - cargo clippy -- -D warnings
  # in order to also check tests and non-default crate features, use
  - cargo clippy --all-targets --all-features -- -D warnings
  - cargo test
  # etc.

Note that adding -D warnings will cause your build to fail if any warnings are found in your code. That includes warnings found by rustc (e.g. dead_code, etc.). If you want to avoid this and only cause an error for Clippy warnings, use #![deny(clippy::all)] in your code or -D clippy::all on the command line. (You can swap clippy::all with the specific lint category you are targeting.)

Configuration

Some lints can be configured in a TOML file named clippy.toml or .clippy.toml. It contains a basic variable = value mapping eg.

avoid-breaking-exported-api = false
blacklisted-names = ["toto", "tata", "titi"]
cognitive-complexity-threshold = 30

See the list of lints for more information about which lints can be configured and the meaning of the variables.

To deactivate the “for further information visit lint-link” message you can define the CLIPPY_DISABLE_DOCS_LINKS environment variable.

Allowing/denying lints

You can add options to your code to allow/warn/deny Clippy lints:

  • the whole set of Warn lints using the clippy lint group (#![deny(clippy::all)])

  • all lints using both the clippy and clippy::pedantic lint groups (#![deny(clippy::all)], #![deny(clippy::pedantic)]). Note that clippy::pedantic contains some very aggressive lints prone to false positives.

  • only some lints (#![deny(clippy::single_match, clippy::box_vec)], etc.)

  • allow/warn/deny can be limited to a single function or module using #[allow(...)], etc.

Note: allow means to suppress the lint for your code. With warn the lint will only emit a warning, while with deny the lint will emit an error, when triggering for your code. An error causes clippy to exit with an error code, so is useful in scripts like CI/CD.

If you do not want to include your lint levels in your code, you can globally enable/disable lints by passing extra flags to Clippy during the run:

To allow lint_name, run

cargo clippy -- -A clippy::lint_name

And to warn on lint_name, run

cargo clippy -- -W clippy::lint_name

This also works with lint groups. For example you can run Clippy with warnings for all lints enabled:

cargo clippy -- -W clippy::pedantic

If you care only about a single lint, you can allow all others and then explicitly warn on the lint(s) you are interested in:

cargo clippy -- -A clippy::all -W clippy::useless_format -W clippy::...

Specifying the minimum supported Rust version

Projects that intend to support old versions of Rust can disable lints pertaining to newer features by specifying the minimum supported Rust version (MSRV) in the clippy configuration file.

msrv = "1.30.0"

The MSRV can also be specified as an inner attribute, like below.

#![feature(custom_inner_attributes)]
#![clippy::msrv = "1.30.0"]

fn main() {
  ...
}

You can also omit the patch version when specifying the MSRV, so msrv = 1.30 is equivalent to msrv = 1.30.0.

Note: custom_inner_attributes is an unstable feature so it has to be enabled explicitly.

Lints that recognize this configuration option can be found here

Contributing

If you want to contribute to Clippy, you can find more information in CONTRIBUTING.md.

License

Copyright 2014-2021 The Rust Project Developers

Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option. Files in the project may not be copied, modified, or distributed except according to those terms.

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