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c58a5da7d4
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](
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| .. | ||
| context | ||
| nonstandard_style | ||
| array_into_iter.rs | ||
| async_fn_in_trait.rs | ||
| builtin.rs | ||
| context.rs | ||
| deref_into_dyn_supertrait.rs | ||
| drop_forget_useless.rs | ||
| early.rs | ||
| enum_intrinsics_non_enums.rs | ||
| errors.rs | ||
| expect.rs | ||
| for_loops_over_fallibles.rs | ||
| foreign_modules.rs | ||
| hidden_unicode_codepoints.rs | ||
| internal.rs | ||
| invalid_from_utf8.rs | ||
| late.rs | ||
| let_underscore.rs | ||
| levels.rs | ||
| lib.rs | ||
| lints.rs | ||
| map_unit_fn.rs | ||
| methods.rs | ||
| multiple_supertrait_upcastable.rs | ||
| non_ascii_idents.rs | ||
| non_fmt_panic.rs | ||
| nonstandard_style.rs | ||
| noop_method_call.rs | ||
| opaque_hidden_inferred_bound.rs | ||
| pass_by_value.rs | ||
| passes.rs | ||
| ptr_nulls.rs | ||
| redundant_semicolon.rs | ||
| reference_casting.rs | ||
| tests.rs | ||
| traits.rs | ||
| types.rs | ||
| unit_bindings.rs | ||
| unused.rs | ||