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bors c58a5da7d4 Auto merge of #119930 - Urgau:check-cfg-empty-values-means-empty, r=petrochenkov 
Add way to express that no values are expected with check-cfg

This PR adds way to express no-values (no values expected) with `--check-cfg` by making empty `values()` no longer mean `values(none())` (internal: `&[None]`) and now be an empty list (internal: `&[]`).

### Context

Currently `--check-cfg` has a way to express that _any value is expected_ with `values(any())`, but has no way to do the inverse and say that _no value is expected_.

This would be particularly useful for build systems that control a config name and it's values as they could always declare a config name as expected and if in the current state they have values pass them and if not pass an empty list.

To give a more concrete example, Cargo `--check-cfg` currently needs to generate:
 - `--check-cfg=cfg(feature, values(...))` for the case with declared features
 - and `--check-cfg=cfg()` for the case without any features declared

This means that when there are no features declared, users will get an `unexpected config name` but from the point of view of Cargo the config name `feature` is expected, it's just that for now there aren't any values for it.

See [Cargo `check_cfg_args` function](92395d9010/src/cargo/core/compiler/mod.rs (L1263-L1281)) for more details.

### De-specializing *empty* `values()`

To solve this issue I propose that we "de-specialize" empty `values()` to no longer mean `values(none())` but to actually mean empty set/list. This is one of the last source of confusion for my-self and others with the `--check-cfg` syntax.

> The confusing part here is that an empty `values()` currently means the same as `values(none())`, i.e. an expected list of values with the _none_ variant (as in `#[cfg(name)]` where the value is none) instead of meaning an empty set.

Before the new `cfg()` syntax, defining the _none_ variant was only possible under certain circumstances, so in https://github.com/rust-lang/rust/pull/111068 I decided to make `values()` to mean the _none_ variant, but it is no longer necessary since https://github.com/rust-lang/rust/pull/119473 which introduced the `none()` syntax.

A simplified representation of the proposed "de-specialization" would be:

| Syntax                                  | List/set of expected values |
|-----------------------------------------|-----------------------------|
| `cfg(name)`/`cfg(name, values(none()))` | `&[None]`                   |
| `cfg(name, values())`                   | `&[]`                       |

Note that I have my-self made the mistake of using an empty `values()` as meaning empty set, see https://github.com/rust-lang/cargo/pull/13011.

`@rustbot` label +F-check-cfg
r? `@petrochenkov`
cc `@epage`
2024-01-17 14:01:05 +00:00
.github Ask for rustc version in diagnostic reports, remind users to update their toolchain 2024-01-07 02:09:55 +00:00
.reuse Rollup merge of #119189 - henrispriet:move-installing-from-source, r=Mark-Simulacrum 2024-01-13 22:35:08 +01:00
compiler Auto merge of #119930 - Urgau:check-cfg-empty-values-means-empty, r=petrochenkov 2024-01-17 14:01:05 +00:00
library proc_macro_c_str_literals: Implement Literal::c_string constructor 2024-01-16 13:27:58 -08:00
LICENSES Add missing CC-BY-SA-4.0. 2023-11-27 11:03:53 +00:00
src Auto merge of #119930 - Urgau:check-cfg-empty-values-means-empty, r=petrochenkov 2024-01-17 14:01:05 +00:00
tests Auto merge of #119930 - Urgau:check-cfg-empty-values-means-empty, r=petrochenkov 2024-01-17 14:01:05 +00:00
.editorconfig Only use max_line_length = 100 for *.rs 2023-07-10 15:18:36 -07:00
.git-blame-ignore-revs Ignore let-chains formatting 2023-10-15 18:30:34 +00:00
.gitattributes Rename config.toml.example to config.example.toml 2023-03-11 14:10:00 -08:00
.gitignore don't globally ignore rustc-ice files 2023-09-16 09:44:44 +02:00
.gitmodules Update to LLVM 17.0.6 2023-12-14 09:54:14 +01:00
.mailmap Add my work email to the mailmap 2023-11-26 18:39:38 +01:00
Cargo.lock Auto merge of #119111 - michaelwoerister:measureme-11, r=Mark-Simulacrum 2024-01-17 09:32:03 +00:00
Cargo.toml Bump salsa 2024-01-10 08:47:26 +01:00
CODE_OF_CONDUCT.md Remove the code of conduct; instead link https://www.rust-lang.org/conduct.html 2019-10-05 22:55:19 +02:00
config.example.toml add a new optimized_compiler_builtins option 2024-01-07 13:04:40 +03:00
configure Enforce Python 3 as much as possible 2020-04-10 09:09:58 -04:00
CONTRIBUTING.md fix: Update CONTRIBUTING.md recommend -> recommended 2023-11-16 23:57:09 +05:30
COPYRIGHT Update COPYRIGHT file 2022-10-30 10:23:14 -04:00
INSTALL.md Move section "Installing from Source" to seperate file 2024-01-13 17:22:55 +01:00
LICENSE-APACHE Remove appendix from LICENCE-APACHE 2019-12-30 14:25:53 +00:00
LICENSE-MIT LICENSE-MIT: Remove inaccurate (misattributed) copyright notice 2017-07-26 16:51:58 -07:00
README.md Move section "Installing from Source" to seperate file 2024-01-13 17:22:55 +01:00
RELEASES.md apply last suggestions from code review 2023-12-21 13:26:15 +01:00
rust-bors.toml Add integration for new bors 2023-09-28 10:43:24 +02:00
rustfmt.toml rustfmt.toml: don't ignore just any tests path, only root one 2024-01-11 14:59:59 +03:00
triagebot.toml Remove Zulip rustdoc nomination alert 2024-01-14 13:55:18 +01:00
x Make x capable of resolving symlinks 2023-10-14 17:53:33 +03:00
x.ps1 use & instead of start-process in x.ps1 2023-12-09 09:46:16 -05:00
x.py Fix recent python linting errors 2023-08-02 04:40:28 -04:00

README.md

The Rust Programming Language

Rust Community

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Note: this README is for users rather than contributors. If you wish to contribute to the compiler, you should read CONTRIBUTING.md instead.

Table of Contents

Quick Start

Read "Installation" from The Book.

Installing from source

If you really want to install from source (though this is not recommended), see INSTALL.md.

Getting Help

See https://www.rust-lang.org/community for a list of chat platforms and forums.

Contributing

See CONTRIBUTING.md.

License

Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.

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The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the "Rust Trademarks").

If you want to use these names or brands, please read the media guide.

Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.