运行rustfmt遇‘不稳定特性仅在nightly通道可用’警告如何解决？

问题背景 #

已将Rust更新至rustc 1.63.0 (4b91a6ea7 2022-08-08)，配置的.rustfmt.toml内容如下：

# Basic
hard_tabs = true
max_width = 100
use_small_heuristics = "Max"

# Imports
imports_granularity = "Crate"
reorder_imports = true

# Consistency
newline_style = "Unix"

# Misc
binop_separator = "Back"
chain_width = 80
match_arm_blocks = false
match_arm_leading_pipes = "Preserve"
match_block_trailing_comma = true
reorder_impl_items = false
spaces_around_ranges = false
trailing_comma = "Vertical"
trailing_semicolon = false
use_field_init_shorthand = true

通过以下命令安装nightly版rustfmt：

rustup toolchain add nightly && rustup component add rustfmt --toolchain nightly

工具链反馈为nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.65.0-nightly (015a824f2 2022-08-22)，但执行格式化命令时：

cargo +nightly fmt
cargo fmt --check

出现多条特性不可用的警告：

Warning: can't set imports_granularity = Crate, unstable features are only available in nightly channel.
Warning: can't set reorder_impl_items = false, unstable features are only available in nightly channel.
Warning: can't set spaces_around_ranges = false, unstable features are only available in nightly channel.
Warning: can't set binop_separator = Back, unstable features are only available in nightly channel.
Warning: can't set match_arm_blocks = false, unstable features are only available in nightly channel.
Warning: can't set trailing_semicolon = false, unstable features are only available in nightly channel.
Warning: can't set trailing_comma = Vertical, unstable features are only available in nightly channel.

问题原因 #

你使用的imports_granularity、reorder_impl_items等配置属于rustfmt的不稳定特性，即使安装了nightly版rustfmt，默认也不会启用这些特性，必须显式声明开启。另外，cargo fmt --check默认调用stable版rustfmt，本身不支持这些特性，因此也会触发警告。

解决步骤 #

1. 启用不稳定特性
   在.rustfmt.toml文件最顶部添加如下配置：

# 开启rustfmt不稳定特性支持
unstable_features = true

2. 统一使用nightly工具链运行格式化
   后续执行格式化或检查命令时，必须指定nightly工具链，避免调用stable版：

# 格式化代码
cargo +nightly fmt
# 检查代码格式
cargo +nightly fmt --check

补充说明 #

如果后续Rust stable版将这些特性纳入稳定支持，你可以移除unstable_features = true配置，改用cargo fmt和cargo fmt --check命令即可。

内容的提问来源于stack exchange，提问作者Russo