Add PreviewMode option to formatter

## Summary

This PR adds the `--preview` and `--no-preview` options to the `format` command (hidden) and passes it through to the formatte. 

## Test Plan

I added the `dbg(f.options().preview())` statement in `FormatNodeRule::fmt` and verified that the option gets correctly passed to the formatter.

Author: MichaReiser

Cargo.lock

@@ -368,6 +368,12 @@ pub struct FormatCommand {
     /// The name of the file when passing it through stdin.
     #[arg(long, help_heading = "Miscellaneous")]
     pub stdin_filename: Option<PathBuf>,
+
+    /// Enable preview mode; checks will include unstable rules and fixes.
+    #[arg(long, overrides_with("no_preview"), hide = true)]
+    preview: bool,
+    #[clap(long, overrides_with("preview"), hide = true)]
+    no_preview: bool,
 }
 
 #[derive(Debug, Clone, Copy, clap::ValueEnum)]
@@ -496,6 +502,7 @@ impl FormatCommand {
                     self.respect_gitignore,
                     self.no_respect_gitignore,
                 ),
+                preview: resolve_bool_arg(self.preview, self.no_preview).map(PreviewMode::from),
                 force_exclude: resolve_bool_arg(self.force_exclude, self.no_force_exclude),
                 // Unsupported on the formatter CLI, but required on `Overrides`.
                 ..Overrides::default()

crates/ruff_cli/src/args.rs

@@ -13,6 +13,7 @@ use tracing::{debug, warn};
 
 use ruff::fs;
 use ruff::logging::LogLevel;
+use ruff::settings::types::PreviewMode;
 use ruff::warn_user_once;
 use ruff_formatter::LineWidth;
 use ruff_python_ast::{PySourceType, SourceType};
@@ -72,9 +73,15 @@ pub(crate) fn format(
                         return None;
                     };
 
+                    let preview = match pyproject_config.settings.lib.preview {
+                        PreviewMode::Enabled => ruff_python_formatter::PreviewMode::Enabled,
+                        PreviewMode::Disabled => ruff_python_formatter::PreviewMode::Disabled,
+                    };
+
                     let line_length = resolver.resolve(path, &pyproject_config).line_length;
                     let options = PyFormatOptions::from_source_type(source_type)
-                        .with_line_width(LineWidth::from(NonZeroU16::from(line_length)));
+                        .with_line_width(LineWidth::from(NonZeroU16::from(line_length)))
+                        .with_preview(preview);
                     debug!("Formatting {} with {:?}", path.display(), options);
                     Some(format_path(path, options, mode))
                 }

crates/ruff_cli/src/commands/format.rs

@@ -23,7 +23,6 @@ anyhow = { workspace = true }
 bitflags = { workspace = true }
 clap = { workspace = true }
 countme = "3.0.1"
-is-macro = { workspace = true }
 itertools = { workspace = true }
 memchr = { workspace = true }
 once_cell = { workspace = true }

crates/ruff_python_formatter/Cargo.toml

@@ -388,10 +388,10 @@ fn can_omit_optional_parentheses(expr: &Expr, context: &PyFormatContext) -> bool
         // Only use the layout if the first or last expression has parentheses of some sort, and
         // those parentheses are non-empty.
         let first_parenthesized = visitor.first.is_some_and(|first| {
-            has_parentheses(first, context).is_some_and(|parentheses| parentheses.is_non_empty())
+            has_parentheses(first, context).is_some_and(OwnParentheses::is_non_empty)
         });
         let last_parenthesized = visitor.last.is_some_and(|last| {
-            has_parentheses(last, context).is_some_and(|parentheses| parentheses.is_non_empty())
+            has_parentheses(last, context).is_some_and(OwnParentheses::is_non_empty)
         });
         first_parenthesized || last_parenthesized
     }
@@ -706,14 +706,20 @@ impl CallChainLayout {
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, is_macro::Is)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub(crate) enum OwnParentheses {
     /// The node has parentheses, but they are empty (e.g., `[]` or `f()`).
     Empty,
     /// The node has parentheses, and they are non-empty (e.g., `[1]` or `f(1)`).
     NonEmpty,
 }
 
+impl OwnParentheses {
+    const fn is_non_empty(self) -> bool {
+        matches!(self, OwnParentheses::NonEmpty)
+    }
+}
+
 /// Returns the [`OwnParentheses`] value for a given [`Expr`], to indicate whether it has its
 /// own parentheses or is itself parenthesized.
 ///

crates/ruff_python_formatter/src/expression/mod.rs

@@ -14,7 +14,7 @@ use crate::comments::{
     dangling_comments, leading_comments, trailing_comments, Comments, SourceComment,
 };
 pub use crate::context::PyFormatContext;
-pub use crate::options::{MagicTrailingComma, PyFormatOptions, QuoteStyle};
+pub use crate::options::{MagicTrailingComma, PreviewMode, PyFormatOptions, QuoteStyle};
 use crate::verbatim::suppressed_node;
 
 pub(crate) mod builders;

crates/ruff_python_formatter/src/lib.rs

@@ -39,6 +39,9 @@ pub struct PyFormatOptions {
     /// Should the formatter generate a source map that allows mapping source positions to positions
     /// in the formatted document.
     source_map_generation: SourceMapGeneration,
+
+    /// Whether preview style formatting is enabled or not
+    preview: PreviewMode,
 }
 
 fn default_line_width() -> LineWidth {
@@ -64,6 +67,7 @@ impl Default for PyFormatOptions {
             line_ending: LineEnding::default(),
             magic_trailing_comma: MagicTrailingComma::default(),
             source_map_generation: SourceMapGeneration::default(),
+            preview: PreviewMode::default(),
         }
     }
 }
@@ -101,6 +105,10 @@ impl PyFormatOptions {
         self.line_ending
     }
 
+    pub fn preview(&self) -> PreviewMode {
+        self.preview
+    }
+
     #[must_use]
     pub fn with_tab_width(mut self, tab_width: TabWidth) -> Self {
         self.tab_width = tab_width;
@@ -136,6 +144,12 @@ impl PyFormatOptions {
         self.line_ending = line_ending;
         self
     }
+
+    #[must_use]
+    pub fn with_preview(mut self, preview: PreviewMode) -> Self {
+        self.preview = preview;
+        self
+    }
 }
 
 impl FormatOptions for PyFormatOptions {
@@ -246,3 +260,18 @@ impl FromStr for MagicTrailingComma {
         }
     }
 }
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Default)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub enum PreviewMode {
+    #[default]
+    Disabled,
+
+    Enabled,
+}
+
+impl PreviewMode {
+    pub const fn is_enabled(self) -> bool {
+        matches!(self, PreviewMode::Enabled)
+    }
+}