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Fix the documentation of the unstable_features option. #5647

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Fix the documentation of the unstable_features option. #5647

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5 changes: 2 additions & 3 deletions Configurations.md
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Expand Up @@ -10,8 +10,7 @@ reorder_imports = false
```

Each configuration option is either stable or unstable.
Stable options can always be used, while unstable options are only available on a nightly toolchain and must be opted into.
To enable unstable options, set `unstable_features = true` in `rustfmt.toml` or pass `--unstable-features` to rustfmt.
Stable options can always be used, while unstable options are only available on a nightly toolchain.

# Configuration Options

Expand Down Expand Up @@ -2734,7 +2733,7 @@ fn lorem<Ipsum: Dolor+Sit=Amet>() {

## `unstable_features`

Enable unstable features on the unstable channel.
**Deperacted and ignored.** Formerly used to enable unstable features on the unstable channel. Unstable features are now activated regardless of whether this option is present or not.
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I did some digging and it turns out that the --unstable_features flag turns on whether or not you can pass --skip-children, --error-on-unformatted or --file-lines via the command line. Here's the reference in the source code

Try running: rustfmt +nightly --skip-children --error-on-unformatted --file-lines "[]" and you'll get the following output:

Unstable options (`--skip-children`, `--error-on-unformatted`, `--file-lines`) used without `--unstable-features`

Also note the (unstable) output for these options using of rustfmt +nightly --help (emphasis with '*' added by me):

        --file-lines JSON
                        Format specified line ranges. Run with
                        `--help=file-lines` for more detail **(unstable)**.
        --error-on-unformatted 
                        Error if unable to get comments or string literals
                        within max_width, or they are left with trailing
                        whitespaces **(unstable)**.
        --skip-children 
                        Don't reformat child modules **(unstable)**.

Trying to run rustfmt +stable --skip-children, rustfmt +stable --error-on-unformatted, or rustfmt +stable --file-lines "[]" results in an error because these options are only added to the command line interface on nightly :

Unrecognized option: 'skip-children'
Unrecognized option: 'error-on-unformatted'
Unrecognized option: 'file-lines'


- **Default value**: `false`
- **Possible values**: `true`, `false`
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