Rollup merge of #95166 - Urgau:check-cfg-values-unstable-book, r=petrochenkov
Update the unstable book with the new `values()` form of check-cfg Forgot to update the unstable book in https://github.com/rust-lang/rust/pull/94362 r? ``@petrochenkov``
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@ -92,8 +92,6 @@ and `cfg!(name = "value")` call. It will check that the `"value"` specified is p
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list of expected values. If `"value"` is not in it, then `rustc` will report an `unexpected_cfgs`
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list of expected values. If `"value"` is not in it, then `rustc` will report an `unexpected_cfgs`
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lint diagnostic. The default diagnostic level for this lint is `Warn`.
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lint diagnostic. The default diagnostic level for this lint is `Warn`.
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The form `values()` is an error, because it does not specify a condition name.
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To enable checking of values, but to provide an empty set of valid values, use this form:
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To enable checking of values, but to provide an empty set of valid values, use this form:
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```bash
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```bash
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@ -104,13 +102,17 @@ The `--check-cfg values(...)` option can be repeated, both for the same conditio
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different names. If it is repeated for the same condition name, then the sets of values for that
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different names. If it is repeated for the same condition name, then the sets of values for that
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condition are merged together.
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condition are merged together.
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If `values()` is specified, then `rustc` will enable the checking of well-known values defined
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by itself. Note that it's necessary to specify the `values()` form to enable the checking of
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well known values, specifying the other forms doesn't implicitly enable it.
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## Examples
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## Examples
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Consider this command line:
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Consider this command line:
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```bash
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```bash
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rustc --check-cfg 'names(feature)' \
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rustc --check-cfg 'names(feature)' \
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--check-cfg 'values(feature,"lion","zebra")' \
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--check-cfg 'values(feature, "lion", "zebra")' \
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--cfg 'feature="lion"' -Z unstable-options \
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--cfg 'feature="lion"' -Z unstable-options \
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example.rs
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example.rs
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```
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```
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