Rollup merge of #111072 - Urgau:check-cfg-new-syntax, r=petrochenkov

Add new simpler and more explicit syntax for check-cfg

<details>
<summary>
Old proposition (before the MCP)
</summary>

This PR adds a new simpler and more explicit syntax for check-cfg. It consist of two new form:
 - `exhaustive(names, values)`
 - `configure(name, "value1", "value2", ... "valueN")`

The preview forms `names(...)` and `values(...)` have implicit meaning that are not strait-forward. In particular `values(foo)`&`values(bar)` and `names(foo, bar)` are not equivalent which has created [some confusions](https://github.com/rust-lang/rust/pull/98080).

Also the `names()` and `values()` form are not clear either and again created some confusions where peoples believed that `values()`&`values(foo)` could be reduced to just `values(foo)`.

To fix that the two new forms are made to be explicit and simpler. See the table of correspondence:
  - `names()` -> `exhaustive(names)`
  - `values()` -> `exhaustive(values)`
  - `names(foo)` -> `exhaustive(names)`&`configure(foo)`
  - `values(foo)` -> `configure(foo)`
  - `values(feat, "foo", "bar")` -> `configure(feat, "foo", "bar")`
  - `values(foo)`&`values(bar)` -> `configure(foo, bar)`
  - `names()`&`values()`&`values(my_cfg)` -> `exhaustive(names, values)`&`configure(my_cfg)`

Another benefits of the new syntax is that it allow for further options (like conditional checking for --cfg, currently always on) without syntax change.

The two previous forms are deprecated and will be removed once cargo and beta rustc have the necessary support.

</details>

This PR is the first part of the implementation of [MCP636 - Simplify and improve explicitness of the check-cfg syntax](https://github.com/rust-lang/compiler-team/issues/636).

## New `cfg` form

It introduces the new [`cfg` form](https://github.com/rust-lang/compiler-team/issues/636) and deprecate the other two:
```
rustc --check-cfg 'cfg(name1, ..., nameN, values("value1", "value2", ... "valueN"))'
```

## Default built-in names and values

It also changes the default for the built-in names and values checking.

 - Built-in values checking would always be activated as long as a `--check-cfg` argument is present
 - Built-in names checking would always be activated as long as a `--check-cfg` argument is present **unless** if any `cfg(any())` arg is passed

~~**Note: depends on https://github.com/rust-lang/rust/pull/111068 but is reviewable (last two commits)!**~~

Resolve https://github.com/rust-lang/compiler-team/issues/636

r? `@petrochenkov`

1 files changed, 2 insertions, 2 deletions

diff --git a/src/doc/rustdoc/src/unstable-features.md b/src/doc/rustdoc/src/unstable-features.md
index 199b5d69a1c..41602dec44c 100644
--- a/src/doc/rustdoc/src/unstable-features.md
+++ b/src/doc/rustdoc/src/unstable-features.md
@@ -628,10 +628,10 @@ Using this flag looks like this:
 
 ```bash
 $ rustdoc src/lib.rs -Z unstable-options \
-    --check-cfg='names()' --check-cfg='values(feature, "foo", "bar")'
+    --check-cfg='cfg(feature, values("foo", "bar"))'
 ```
 
-The example above check every well known names (`target_os`, `doc`, `test`, ... via `names()`)
+The example above check every well known names and values (`target_os`, `doc`, `test`, ...)
 and check the values of `feature`: `foo` and `bar`.
 
 ### `--generate-link-to-definition`: Generate links on types in source code