Skip to content

Update the unstable book with the new values() form of check-cfg #95166

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Mar 21, 2022
Merged

Update the unstable book with the new values() form of check-cfg #95166

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 5 additions & 3 deletions src/doc/unstable-book/src/compiler-flags/check-cfg.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -92,8 +92,6 @@ and `cfg!(name = "value")` call. It will check that the `"value"` specified is p
list of expected values. If `"value"` is not in it, then `rustc` will report an `unexpected_cfgs`
lint diagnostic. The default diagnostic level for this lint is `Warn`.

The form `values()` is an error, because it does not specify a condition name.

To enable checking of values, but to provide an empty set of valid values, use this form:

```bash
Expand All @@ -104,13 +102,17 @@ The `--check-cfg values(...)` option can be repeated, both for the same conditio
different names. If it is repeated for the same condition name, then the sets of values for that
condition are merged together.

If `values()` is specified, then `rustc` will enable the checking of well-known values defined
by itself. Note that it's necessary to specify the `values()` form to enable the checking of
well known values, specifying the other forms doesn't implicitly enable it.

## Examples

Consider this command line:

```bash
rustc --check-cfg 'names(feature)' \
--check-cfg 'values(feature,"lion","zebra")' \
--check-cfg 'values(feature, "lion", "zebra")' \
--cfg 'feature="lion"' -Z unstable-options \
example.rs
```
Expand Down