Struct TabMap 

pub struct TabMap<'a> { /* private fields */ }

The coordinates seam — a concrete type, not a trait.

Its entire durable state is tab_size; it holds no persisted visual indices, so there is nothing derived that could drift out of sync with the text. Built per frame from the document’s tab_size plus a borrow of the buffer’s line index, so every conversion reads live text and the map is current by construction.

Every method that can land on a lossy position (mid-tab, or inside a fold at the layer above) threads Bias from the start, so no call site needs retrofitting when a new lossy case appears.

Implementations

impl<'a> TabMap<'a>

pub fn new(lines: &'a Buffer, tab_size: u32) -> Self

A map over lines with the given tab stop width. tab_size is expected to be ≥ 1 (see default_tab_size).

pub fn to_display(&self, point: Point, _bias: Bias) -> DisplayPoint

Buffer → display. point.col is a char-boundary byte column (the buffer guarantees this); the result column is cells. Total: every valid buffer point maps to exactly one display point, so bias is irrelevant here.

pub fn to_buffer(&self, point: DisplayPoint, bias: Bias) -> Point

Display → buffer, with the bias snap: if point.col falls strictly inside a tab expansion it is not a caret slot — Left yields the byte of the \t, Right the byte after it.

pub fn clip(&self, point: DisplayPoint, bias: Bias) -> DisplayPoint

Snap any externally-sourced display position (mouse hit, diagnostic span, find match) to the nearest valid caret slot — the guard every such position passes before use. Steps: collapse by bias → clamp + char snap in buffer space → re-expand. Idempotent.

pub fn max_point(&self) -> DisplayPoint

The bottom-right valid position: the last row and its cell length.

pub fn row_count(&self) -> u32

Number of display rows in this map — the buffer line count. (Hiding rows is the FoldMap layer’s job, above this one.)

pub fn line_len(&self, row: DisplayRow) -> u32

Cell width of a display row (the whole line expanded).

pub fn row_info(&self, row: DisplayRow) -> Option<BufferRow>

Gutter protocol: the buffer line number to print. Always Some in this map; the Option lets a caller handle a display row that has no printed line number.

pub fn sync(&mut self, _buffer_patch: &Patch)

Consume the transaction’s buffer-space edit patch and splice any internal derived state. Returns (): downstream caches (line cache, paragraph cache) invalidate off the buffer-space LineSplice they already consume, so no display-space edit vector is emitted — widen to Vec<DisplayEdit> only if a display-space reader ever appears. The map holds no derived state, so this is a no-op; the borrow of live buffer text keeps every conversion current by construction.

pub fn max_row(&self) -> DisplayRow

The last display row. row_count − 1, saturating.