Add tab width option (#6848)

crates/ruff_formatter/src/lib.rs

@@ -51,7 +51,7 @@ pub use crate::diagnostics::{ActualStart, FormatError, InvalidDocumentError, Pri
 pub use format_element::{normalize_newlines, FormatElement, LINE_TERMINATORS};
 pub use group_id::GroupId;
 use ruff_text_size::{TextRange, TextSize};
-use std::num::ParseIntError;
+use std::num::{NonZeroU8, ParseIntError, TryFromIntError};
 use std::str::FromStr;
 
 #[derive(Debug, Eq, PartialEq, Clone, Copy, Hash)]
@@ -108,6 +108,33 @@ impl std::fmt::Display for IndentStyle {
     }
 }
 
+/// The visual width of a `\t` character.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct TabWidth(NonZeroU8);
+
+impl TabWidth {
+    /// Return the numeric value for this [`LineWidth`]
+    pub const fn value(&self) -> u32 {
+        self.0.get() as u32
+    }
+}
+
+impl Default for TabWidth {
+    fn default() -> Self {
+        Self(NonZeroU8::new(2).unwrap())
+    }
+}
+
+impl TryFrom<u8> for TabWidth {
+    type Error = TryFromIntError;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        NonZeroU8::try_from(value).map(Self)
+    }
+}
+
 /// Validated value for the `line_width` formatter options
 ///
 /// The allowed range of values is 1..=320
@@ -213,6 +240,17 @@ pub trait FormatOptions {
     /// The indent style.
     fn indent_style(&self) -> IndentStyle;
 
+    /// The visual width of a tab character.
+    fn tab_width(&self) -> TabWidth;
+
+    /// The visual width of an indent
+    fn indent_width(&self) -> u32 {
+        match self.indent_style() {
+            IndentStyle::Tab => self.tab_width().value(),
+            IndentStyle::Space(spaces) => u32::from(spaces),
+        }
+    }
+
     /// What's the max width of a line. Defaults to 80.
     fn line_width(&self) -> LineWidth;
 
@@ -264,6 +302,10 @@ impl FormatOptions for SimpleFormatOptions {
         self.indent_style
     }
 
+    fn tab_width(&self) -> TabWidth {
+        TabWidth::default()
+    }
+
     fn line_width(&self) -> LineWidth {
         self.line_width
     }
@@ -271,6 +313,7 @@ impl FormatOptions for SimpleFormatOptions {
     fn as_print_options(&self) -> PrinterOptions {
         PrinterOptions::default()
             .with_indent(self.indent_style)
+            .with_tab_width(self.tab_width())
             .with_print_width(self.line_width.into())
     }
 }