Introduce tab-size to correcly calculate the line length with tabulations (#4167)

crates/ruff/src/line_width.rs

@@ -0,0 +1,165 @@
+use serde::{Deserialize, Serialize};
+use unicode_width::UnicodeWidthChar;
+
+use ruff_macros::CacheKey;
+
+/// The length of a line of text that is considered too long.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize, CacheKey)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct LineLength(usize);
+
+impl Default for LineLength {
+    /// The default line length.
+    fn default() -> Self {
+        Self(88)
+    }
+}
+
+impl LineLength {
+    pub const fn get(&self) -> usize {
+        self.0
+    }
+}
+
+impl From<usize> for LineLength {
+    fn from(value: usize) -> Self {
+        Self(value)
+    }
+}
+
+/// A measure of the width of a line of text.
+///
+/// This is used to determine if a line is too long.
+/// It should be compared to a [`LineLength`].
+#[derive(Clone, Copy, Debug)]
+pub struct LineWidth {
+    /// The width of the line.
+    width: usize,
+    /// The column of the line.
+    /// This is used to calculate the width of tabs.
+    column: usize,
+    /// The tab size to use when calculating the width of tabs.
+    tab_size: TabSize,
+}
+
+impl Default for LineWidth {
+    fn default() -> Self {
+        Self::new(TabSize::default())
+    }
+}
+
+impl PartialEq for LineWidth {
+    fn eq(&self, other: &Self) -> bool {
+        self.width == other.width
+    }
+}
+
+impl Eq for LineWidth {}
+
+impl PartialOrd for LineWidth {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        self.width.partial_cmp(&other.width)
+    }
+}
+
+impl Ord for LineWidth {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.width.cmp(&other.width)
+    }
+}
+
+impl LineWidth {
+    pub fn get(&self) -> usize {
+        self.width
+    }
+
+    /// Creates a new `LineWidth` with the given tab size.
+    pub fn new(tab_size: TabSize) -> Self {
+        LineWidth {
+            width: 0,
+            column: 0,
+            tab_size,
+        }
+    }
+
+    fn update(mut self, chars: impl Iterator<Item = char>) -> Self {
+        let tab_size: usize = self.tab_size.into();
+        for c in chars {
+            match c {
+                '\t' => {
+                    let tab_offset = tab_size - (self.column % tab_size);
+                    self.width += tab_offset;
+                    self.column += tab_offset;
+                }
+                '\n' | '\r' => {
+                    self.width = 0;
+                    self.column = 0;
+                }
+                _ => {
+                    self.width += c.width().unwrap_or(0);
+                    self.column += 1;
+                }
+            }
+        }
+        self
+    }
+
+    /// Adds the given text to the line width.
+    #[must_use]
+    pub fn add_str(self, text: &str) -> Self {
+        self.update(text.chars())
+    }
+
+    /// Adds the given character to the line width.
+    #[must_use]
+    pub fn add_char(self, c: char) -> Self {
+        self.update(std::iter::once(c))
+    }
+
+    /// Adds the given width to the line width.
+    /// Also adds the given width to the column.
+    /// It is generally better to use [`LineWidth::add_str`] or [`LineWidth::add_char`].
+    /// The width and column should be the same for the corresponding text.
+    /// Currently, this is only used to add spaces.
+    #[must_use]
+    pub fn add_width(mut self, width: usize) -> Self {
+        self.width += width;
+        self.column += width;
+        self
+    }
+}
+
+impl PartialEq<LineLength> for LineWidth {
+    fn eq(&self, other: &LineLength) -> bool {
+        self.width == other.0
+    }
+}
+
+impl PartialOrd<LineLength> for LineWidth {
+    fn partial_cmp(&self, other: &LineLength) -> Option<std::cmp::Ordering> {
+        self.width.partial_cmp(&other.0)
+    }
+}
+
+/// The size of a tab.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize, CacheKey)]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+pub struct TabSize(pub u8);
+
+impl Default for TabSize {
+    fn default() -> Self {
+        Self(4)
+    }
+}
+
+impl From<u8> for TabSize {
+    fn from(tab_size: u8) -> Self {
+        Self(tab_size)
+    }
+}
+
+impl From<TabSize> for usize {
+    fn from(tab_size: TabSize) -> Self {
+        tab_size.0 as usize
+    }
+}