fix: chat input crashing when moving the cursor (#33)

Reviewed-on: #33

crates/ui/src/input/display_map/display_map.rs

@@ -0,0 +1,336 @@
+/// DisplayMap: Public facade for Editor/Input display mapping.
+///
+/// This combines WrapMap and FoldMap to provide a unified API:
+/// - BufferPoint ↔ DisplayPoint conversion
+/// - Fold management (candidates, toggle, query)
+/// - Automatic projection updates on text/layout changes
+use std::ops::Range;
+
+use gpui::{App, Font, Pixels};
+use ropey::Rope;
+
+use super::fold_map::FoldMap;
+use super::folding::FoldRange;
+use super::text_wrapper::{LineItem, WrapDisplayPoint};
+use super::wrap_map::WrapMap;
+use super::{BufferPoint, DisplayPoint};
+use crate::input::display_map::WrapPoint;
+use crate::input::rope_ext::RopeExt as _;
+use crate::input::Point as TreeSitterPoint;
+
+/// DisplayMap is the main interface for Editor/Input coordinate mapping.
+///
+/// It manages the two-layer projection:
+/// 1. Buffer → Wrap (soft-wrapping)
+/// 2. Wrap → Display (folding)
+///
+/// Editor/Input only needs to work with BufferPoint and DisplayPoint.
+pub struct DisplayMap {
+    wrap_map: WrapMap,
+    fold_map: FoldMap,
+}
+
+impl DisplayMap {
+    pub fn new(font: Font, font_size: Pixels, wrap_width: Option<Pixels>) -> Self {
+        Self {
+            wrap_map: WrapMap::new(font, font_size, wrap_width),
+            fold_map: FoldMap::new(),
+        }
+    }
+
+    // ==================== Core Coordinate Mapping ====================
+
+    /// Convert buffer position to display position
+    pub fn buffer_pos_to_display_pos(&self, pos: BufferPoint) -> DisplayPoint {
+        // Buffer → Wrap
+        let wrap_pos = self.wrap_map.buffer_pos_to_wrap_pos(pos);
+
+        // Wrap → Display
+        if let Some(display_row) = self.fold_map.wrap_row_to_display_row(wrap_pos.row) {
+            DisplayPoint::new(display_row, wrap_pos.col)
+        } else {
+            // Cursor is in a folded region, find nearest visible row
+            let display_row = self.fold_map.nearest_visible_display_row(wrap_pos.row);
+            DisplayPoint::new(display_row, 0) // Column 0 at fold boundary
+        }
+    }
+
+    /// Convert display position to buffer position
+    pub fn display_pos_to_buffer_pos(&self, pos: DisplayPoint) -> BufferPoint {
+        // Display → Wrap
+        let wrap_row = self.fold_map.display_row_to_wrap_row(pos.row).unwrap_or(0);
+
+        // Wrap → Buffer
+        let wrap_pos = WrapPoint::new(wrap_row, pos.col);
+        self.wrap_map.wrap_pos_to_buffer_pos(wrap_pos)
+    }
+
+    /// Get total number of visible display rows
+    #[inline]
+    pub fn display_row_count(&self) -> usize {
+        self.fold_map.display_row_count()
+    }
+
+    /// Get the buffer line for a given display row
+    pub fn display_row_to_buffer_line(&self, display_row: usize) -> usize {
+        // Display → Wrap
+        let wrap_row = self
+            .fold_map
+            .display_row_to_wrap_row(display_row)
+            .unwrap_or(0);
+
+        // Wrap → Buffer line
+        self.wrap_map.wrap_row_to_buffer_line(wrap_row)
+    }
+
+    /// Get the display row range for a buffer line: [start, end)
+    /// Returns None if the buffer line is completely hidden
+    pub fn buffer_line_to_display_row_range(&self, line: usize) -> Option<Range<usize>> {
+        // Buffer line → Wrap row range
+        let wrap_row_range = self.wrap_map.buffer_line_to_wrap_row_range(line);
+
+        // Find first and last visible display rows in this range
+        let mut first_display_row = None;
+        let mut last_display_row = None;
+
+        for wrap_row in wrap_row_range {
+            if let Some(display_row) = self.fold_map.wrap_row_to_display_row(wrap_row) {
+                if first_display_row.is_none() {
+                    first_display_row = Some(display_row);
+                }
+                last_display_row = Some(display_row);
+            }
+        }
+
+        if let (Some(start), Some(end)) = (first_display_row, last_display_row) {
+            Some(start..end + 1)
+        } else {
+            None // Completely folded
+        }
+    }
+
+    /// Check if a buffer line is completely hidden
+    #[inline]
+    pub fn is_buffer_line_hidden(&self, line: usize) -> bool {
+        self.buffer_line_to_display_row_range(line).is_none()
+    }
+
+    /// Set fold candidates (from tree-sitter/LSP)
+    pub fn set_fold_candidates(&mut self, candidates: Vec<FoldRange>) {
+        self.fold_map.set_candidates(candidates);
+        self.rebuild_fold_projection();
+    }
+
+    /// Set a fold at the given start_line (must be in candidates)
+    pub fn set_folded(&mut self, start_line: usize, folded: bool) {
+        self.fold_map.set_folded(start_line, folded);
+        self.rebuild_fold_projection();
+    }
+
+    /// Toggle fold at the given start_line
+    pub fn toggle_fold(&mut self, start_line: usize) {
+        self.fold_map.toggle_fold(start_line);
+        self.rebuild_fold_projection();
+    }
+
+    /// Check if a line is currently folded
+    #[inline]
+    pub fn is_folded_at(&self, start_line: usize) -> bool {
+        self.fold_map.is_folded_at(start_line)
+    }
+
+    /// Check if a line is a fold candidate
+    #[inline]
+    pub fn is_fold_candidate(&self, start_line: usize) -> bool {
+        self.fold_map.is_fold_candidate(start_line)
+    }
+
+    /// Get all currently folded ranges
+    #[inline]
+    pub fn folded_ranges(&self) -> &[FoldRange] {
+        self.fold_map.folded_ranges()
+    }
+
+    /// Clear all folds
+    pub fn clear_folds(&mut self) {
+        self.fold_map.clear_folds();
+        self.rebuild_fold_projection();
+    }
+
+    // ==================== Text and Layout Updates ====================
+
+    /// Adjust folds and candidates for a text edit before updating the wrap map.
+    ///
+    /// Must be called with the OLD text (before replacement) and the edit range/new_text
+    /// so we can compute which old lines were affected.
+    pub fn adjust_folds_for_edit(&mut self, old_text: &Rope, range: &Range<usize>, new_text: &str) {
+        if self.fold_map.folded_ranges().is_empty() && self.fold_map.fold_candidates().is_empty() {
+            return;
+        }
+
+        let edit_start_line = old_text.offset_to_point(range.start).row;
+        let edit_end_line = old_text.offset_to_point(range.end.min(old_text.len())).row;
+
+        let old_lines_in_range = edit_end_line.saturating_sub(edit_start_line);
+        let new_lines_in_range = new_text.chars().filter(|c| *c == '\n').count();
+        let line_delta = new_lines_in_range as isize - old_lines_in_range as isize;
+
+        self.fold_map
+            .adjust_folds_for_edit(edit_start_line, edit_end_line, line_delta);
+    }
+
+    /// Incrementally update fold candidates after a text edit.
+    ///
+    /// Extracts new fold candidates only within the edited byte range
+    /// and merges them with existing (already adjusted) candidates.
+    pub fn update_fold_candidates_for_edit(
+        &mut self,
+        tree: &super::folding::Tree,
+        edit_byte_range: Range<usize>,
+        new_text: &Rope,
+    ) {
+        let new_start_line = new_text.offset_to_point(edit_byte_range.start).row;
+        let new_end_line = new_text
+            .offset_to_point(edit_byte_range.end.min(new_text.len()))
+            .row;
+
+        let new_candidates = super::folding::extract_fold_ranges_in_range(tree, edit_byte_range);
+        self.fold_map
+            .merge_candidates_for_edit(new_start_line, new_end_line, new_candidates);
+    }
+
+    /// Update text (incremental or full)
+    pub fn on_text_changed(
+        &mut self,
+        changed_text: &Rope,
+        range: &Range<usize>,
+        new_text: &Rope,
+        cx: &mut App,
+    ) {
+        self.wrap_map
+            .on_text_changed(changed_text, range, new_text, cx);
+        self.rebuild_fold_projection();
+    }
+
+    /// Update layout parameters (wrap width or font)
+    pub fn on_layout_changed(&mut self, wrap_width: Option<Pixels>, cx: &mut App) {
+        self.wrap_map.on_layout_changed(wrap_width, cx);
+        self.rebuild_fold_projection();
+    }
+
+    /// Set font parameters
+    pub fn set_font(&mut self, font: Font, font_size: Pixels, cx: &mut App) {
+        self.wrap_map.set_font(font, font_size, cx);
+        self.rebuild_fold_projection();
+    }
+
+    /// Ensure text is prepared (initializes wrapper if needed)
+    pub fn ensure_text_prepared(&mut self, text: &Rope, cx: &mut App) {
+        let did_initialize = self.wrap_map.ensure_text_prepared(text, cx);
+        if did_initialize {
+            self.rebuild_fold_projection();
+        }
+    }
+
+    /// Initialize with text
+    pub fn set_text(&mut self, text: &Rope, cx: &mut App) {
+        self.wrap_map.set_text(text, cx);
+        self.rebuild_fold_projection();
+    }
+
+    // ==================== Internal Helpers ====================
+
+    /// Rebuild fold projection after wrap_map or fold state changes
+    /// Only rebuilds if there are actually folded ranges
+    fn rebuild_fold_projection(&mut self) {
+        if !self.fold_map.folded_ranges().is_empty() {
+            self.fold_map.rebuild(&self.wrap_map);
+        } else {
+            // No active folds: identity mapping (wrap_row == display_row).
+            // Just update cached count so query methods work without Vec allocation.
+            self.fold_map
+                .mark_dirty_with_wrap_count(self.wrap_map.wrap_row_count());
+        }
+    }
+
+    // ==================== Wrap Display Point Operations ====================
+
+    /// Convert byte offset to wrap display point (with soft wrap info).
+    #[inline]
+    pub(crate) fn offset_to_wrap_display_point(&self, offset: usize) -> WrapDisplayPoint {
+        self.wrap_map.wrapper().offset_to_display_point(offset)
+    }
+
+    /// Convert wrap display point to byte offset.
+    #[inline]
+    pub(crate) fn wrap_display_point_to_offset(&self, point: WrapDisplayPoint) -> usize {
+        self.wrap_map.wrapper().display_point_to_offset(point)
+    }
+
+    /// Convert wrap display point to TreeSitterPoint (buffer line/col).
+    #[inline]
+    pub(crate) fn wrap_display_point_to_point(
+        &self,
+        point: WrapDisplayPoint,
+    ) -> TreeSitterPoint {
+        self.wrap_map.wrapper().display_point_to_point(point)
+    }
+
+    /// Convert a wrap row to a display row (skipping folded rows).
+    /// Returns None if the wrap row is folded.
+    #[inline]
+    pub fn wrap_row_to_display_row(&self, wrap_row: usize) -> Option<usize> {
+        self.fold_map.wrap_row_to_display_row(wrap_row)
+    }
+
+    /// Find the nearest visible display row for a given wrap row.
+    #[inline]
+    pub fn nearest_visible_display_row(&self, wrap_row: usize) -> usize {
+        self.fold_map.nearest_visible_display_row(wrap_row)
+    }
+
+    /// Convert a display row to a wrap row.
+    #[inline]
+    pub fn display_row_to_wrap_row(&self, display_row: usize) -> Option<usize> {
+        self.fold_map.display_row_to_wrap_row(display_row)
+    }
+
+    /// Get the longest row index (by byte length).
+    #[inline]
+    pub(crate) fn longest_row(&self) -> usize {
+        self.wrap_map.wrapper().longest_row.row
+    }
+
+    // ==================== Access Methods ====================
+
+    /// Get access to line items (for rendering)
+    #[inline]
+    pub(crate) fn lines(&self) -> &[LineItem] {
+        self.wrap_map.lines()
+    }
+
+    /// Get the rope text
+    #[inline]
+    pub fn text(&self) -> &Rope {
+        self.wrap_map.text()
+    }
+
+    /// Calculate how many wrap rows of a buffer line are visible (not folded)
+    #[inline]
+    pub fn visible_wrap_row_count_for_buffer_line(&self, line: usize) -> usize {
+        self.wrap_map
+            .visible_wrap_row_count_for_line(line, &self.fold_map)
+    }
+
+    /// Get the wrap row count (before folding)
+    #[inline]
+    pub fn wrap_row_count(&self) -> usize {
+        self.wrap_map.wrap_row_count()
+    }
+
+    /// Get the buffer line count (logical lines)
+    #[inline]
+    pub fn buffer_line_count(&self) -> usize {
+        self.wrap_map.buffer_line_count()
+    }
+}

crates/ui/src/input/display_map/fold_map.rs

@@ -0,0 +1,343 @@
+/// FoldMap: Folding projection layer (Wrap rows → Display rows).
+///
+/// This module manages code folding by:
+/// - Filtering out wrap rows that belong to folded regions
+/// - Maintaining bidirectional mapping: wrap_row ↔ display_row
+/// - Handling fold state changes and rebuilding the projection
+use super::folding::FoldRange;
+use super::wrap_map::WrapMap;
+
+/// FoldMap projects wrap rows to display rows by hiding folded regions.
+pub struct FoldMap {
+    /// Mapping: display_row → wrap_row
+    /// index = display_row, value = actual wrap_row
+    visible_wrap_rows: Vec<usize>,
+
+    /// Reverse mapping: wrap_row → display_row
+    /// index = wrap_row, value = Some(display_row) if visible, None if folded
+    wrap_row_to_display_row: Vec<Option<usize>>,
+
+    /// Candidate fold ranges (from tree-sitter/LSP)
+    /// Sorted by start_line, unique start_line
+    candidates: Vec<FoldRange>,
+
+    /// Currently folded ranges
+    /// Subset of candidates, sorted by start_line
+    folded: Vec<FoldRange>,
+
+    /// Flag indicating if the fold projection needs rebuilding
+    /// Used for lazy evaluation to avoid expensive rebuilds on every text change
+    needs_rebuild: bool,
+
+    /// Cached wrap_row_count from last rebuild
+    /// Used to detect if WrapMap changed and rebuild is needed
+    cached_wrap_row_count: usize,
+}
+
+impl FoldMap {
+    pub fn new() -> Self {
+        Self {
+            visible_wrap_rows: Vec::new(),
+            wrap_row_to_display_row: Vec::new(),
+            candidates: Vec::new(),
+            folded: Vec::new(),
+            needs_rebuild: true,
+            cached_wrap_row_count: 0,
+        }
+    }
+
+    /// Update cached wrap_row_count without full rebuild.
+    /// Used when no folds are active (identity mapping assumed).
+    pub(super) fn mark_dirty_with_wrap_count(&mut self, wrap_row_count: usize) {
+        self.needs_rebuild = true;
+        self.cached_wrap_row_count = wrap_row_count;
+    }
+
+    /// Get total number of visible display rows
+    pub fn display_row_count(&self) -> usize {
+        if self.folded.is_empty() {
+            return self.cached_wrap_row_count;
+        }
+        self.visible_wrap_rows.len()
+    }
+
+    /// Convert wrap_row to display_row
+    /// Returns None if the wrap_row is hidden by folding
+    pub fn wrap_row_to_display_row(&self, wrap_row: usize) -> Option<usize> {
+        if self.folded.is_empty() {
+            return if wrap_row < self.cached_wrap_row_count {
+                Some(wrap_row)
+            } else {
+                None
+            };
+        }
+        self.wrap_row_to_display_row
+            .get(wrap_row)
+            .copied()
+            .flatten()
+    }
+
+    /// Convert display_row to wrap_row
+    pub fn display_row_to_wrap_row(&self, display_row: usize) -> Option<usize> {
+        if self.folded.is_empty() {
+            return if display_row < self.cached_wrap_row_count {
+                Some(display_row)
+            } else {
+                None
+            };
+        }
+        self.visible_wrap_rows.get(display_row).copied()
+    }
+
+    /// Find the nearest visible display_row for a given wrap_row
+    pub fn nearest_visible_display_row(&self, wrap_row: usize) -> usize {
+        if self.folded.is_empty() {
+            return wrap_row.min(self.cached_wrap_row_count.saturating_sub(1));
+        }
+
+        if let Some(dr) = self.wrap_row_to_display_row(wrap_row) {
+            return dr;
+        }
+
+        match self.visible_wrap_rows.binary_search(&wrap_row) {
+            Ok(idx) => idx,
+            Err(insert_pos) => insert_pos.saturating_sub(1),
+        }
+    }
+
+    /// Set fold candidates (from tree-sitter/LSP), full replacement.
+    pub fn set_candidates(&mut self, mut candidates: Vec<FoldRange>) {
+        // Sort and deduplicate by start_line
+        candidates.sort_by_key(|r| r.start_line);
+        candidates.dedup_by_key(|r| r.start_line);
+        self.candidates = candidates;
+
+        // Remove any folded ranges that are no longer in candidates
+        self.folded.retain(|fold| {
+            self.candidates
+                .iter()
+                .any(|c| c.start_line == fold.start_line)
+        });
+    }
+
+    /// Merge new candidates extracted from an edited region into existing candidates.
+    ///
+    /// Replaces candidates within [edit_start_line, edit_end_line] with `new_candidates`,
+    /// keeping candidates outside the edit range intact.
+    pub fn merge_candidates_for_edit(
+        &mut self,
+        edit_start_line: usize,
+        edit_end_line: usize,
+        new_candidates: Vec<FoldRange>,
+    ) {
+        // Remove old candidates within the edit range (already done by adjust_folds_for_edit)
+        // But do it again in case adjust wasn't called or range differs
+        self.candidates
+            .retain(|c| c.start_line < edit_start_line || c.start_line > edit_end_line);
+
+        // Add new candidates
+        self.candidates.extend(new_candidates);
+        self.candidates.sort_by_key(|r| r.start_line);
+        self.candidates.dedup_by_key(|r| r.start_line);
+    }
+
+    /// Set a fold at the given start_line (must be in candidates)
+    pub fn set_folded(&mut self, start_line: usize, folded: bool) {
+        if folded {
+            // Find the candidate range for this start_line
+            if let Some(candidate) = self.candidates.iter().find(|c| c.start_line == start_line) {
+                // Add to folded if not already present
+                if !self.folded.iter().any(|f| f.start_line == start_line) {
+                    self.folded.push(*candidate);
+                    self.folded.sort_by_key(|r| r.start_line);
+                    self.needs_rebuild = true;
+                }
+            }
+        } else {
+            // Remove from folded
+            self.folded.retain(|f| f.start_line != start_line);
+            self.needs_rebuild = true;
+        }
+    }
+
+    /// Toggle fold at the given start_line
+    pub fn toggle_fold(&mut self, start_line: usize) {
+        let is_folded = self.is_folded_at(start_line);
+        self.set_folded(start_line, !is_folded);
+    }
+
+    /// Check if a line is currently folded
+    pub fn is_folded_at(&self, start_line: usize) -> bool {
+        self.folded.iter().any(|f| f.start_line == start_line)
+    }
+
+    /// Check if a line is a fold candidate
+    pub fn is_fold_candidate(&self, start_line: usize) -> bool {
+        self.candidates.iter().any(|c| c.start_line == start_line)
+    }
+
+    /// Get all fold candidates
+    #[inline]
+    pub fn fold_candidates(&self) -> &[FoldRange] {
+        &self.candidates
+    }
+
+    /// Get all currently folded ranges
+    #[inline]
+    pub fn folded_ranges(&self) -> &[FoldRange] {
+        &self.folded
+    }
+
+    /// Clear all folds
+    #[inline]
+    pub fn clear_folds(&mut self) {
+        self.folded.clear();
+    }
+
+    /// Adjust folds and candidates after a text edit.
+    ///
+    /// - Folds/candidates overlapping the edited line range are removed
+    /// - Folds/candidates after the edit are shifted by line_delta
+    ///
+    /// This avoids expensive full tree traversal on every keystroke.
+    pub fn adjust_folds_for_edit(
+        &mut self,
+        edit_start_line: usize,
+        edit_end_line: usize,
+        line_delta: isize,
+    ) {
+        // Adjust folded ranges
+        if !self.folded.is_empty() {
+            self.folded.retain(|fold| {
+                !(fold.start_line <= edit_end_line && fold.end_line >= edit_start_line)
+            });
+
+            if line_delta != 0 {
+                for fold in &mut self.folded {
+                    if fold.start_line > edit_end_line {
+                        fold.start_line = (fold.start_line as isize + line_delta).max(0) as usize;
+                        fold.end_line = (fold.end_line as isize + line_delta).max(0) as usize;
+                    }
+                }
+            }
+        }
+
+        // Adjust candidates the same way
+        if !self.candidates.is_empty() {
+            self.candidates
+                .retain(|c| !(c.start_line <= edit_end_line && c.end_line >= edit_start_line));
+
+            if line_delta != 0 {
+                for c in &mut self.candidates {
+                    if c.start_line > edit_end_line {
+                        c.start_line = (c.start_line as isize + line_delta).max(0) as usize;
+                        c.end_line = (c.end_line as isize + line_delta).max(0) as usize;
+                    }
+                }
+            }
+        }
+
+        self.needs_rebuild = true;
+    }
+
+    /// Rebuild the fold mapping after wrap_map or fold state changes
+    ///
+    /// This is the core algorithm that projects wrap rows to display rows.
+    pub fn rebuild(&mut self, wrap_map: &WrapMap) {
+        let wrap_row_count = wrap_map.wrap_row_count();
+
+        // Performance optimization: skip rebuild if nothing changed
+        if !self.needs_rebuild && wrap_row_count == self.cached_wrap_row_count {
+            return;
+        }
+
+        self.cached_wrap_row_count = wrap_row_count;
+
+        self.visible_wrap_rows.clear();
+        self.wrap_row_to_display_row = vec![None; wrap_row_count];
+
+        if self.folded.is_empty() {
+            // Fast path: no folds, all wrap rows are visible
+            self.visible_wrap_rows = (0..wrap_row_count).collect();
+            for (display_row, &wrap_row) in self.visible_wrap_rows.iter().enumerate() {
+                self.wrap_row_to_display_row[wrap_row] = Some(display_row);
+            }
+            self.needs_rebuild = false;
+            return;
+        }
+
+        // Build set of hidden wrap_row ranges from folded buffer lines
+        let mut hidden_ranges = Vec::new();
+        for fold in &self.folded {
+            // Hide wrap rows from (start_line + 1) to (end_line - 1) (inclusive)
+            // Both the first line and last line of the fold remain visible
+            let hide_start_line = fold.start_line + 1;
+            let hide_end_line = fold.end_line.saturating_sub(1);
+
+            if hide_start_line > hide_end_line {
+                continue; // No middle lines to hide (0 or 1 lines between start and end)
+            }
+
+            // Get wrap_row ranges for the hidden buffer lines
+            let start_wrap_row = wrap_map.buffer_line_to_first_wrap_row(hide_start_line);
+            let end_wrap_row = if hide_end_line + 1 < wrap_map.buffer_line_count() {
+                wrap_map.buffer_line_to_first_wrap_row(hide_end_line + 1)
+            } else {
+                wrap_row_count
+            };
+
+            if start_wrap_row < end_wrap_row {
+                hidden_ranges.push(start_wrap_row..end_wrap_row);
+            }
+        }
+
+        // Merge overlapping hidden ranges
+        hidden_ranges.sort_by_key(|r| r.start);
+        let mut merged_hidden = Vec::new();
+        for range in hidden_ranges {
+            if let Some(last) = merged_hidden.last_mut() {
+                if range.start <= *last {
+                    // Overlapping or adjacent, merge
+                    *last = (*last).max(range.end);
+                } else {
+                    merged_hidden.push(range.start);
+                    merged_hidden.push(range.end);
+                }
+            } else {
+                merged_hidden.push(range.start);
+                merged_hidden.push(range.end);
+            }
+        }
+
+        // Scan all wrap rows and filter out hidden ones
+        let mut display_row = 0;
+        let mut hidden_iter = merged_hidden.chunks_exact(2);
+        let mut current_hidden = hidden_iter.next();
+
+        for wrap_row in 0..wrap_row_count {
+            // Check if wrap_row is in current hidden range
+            let is_hidden = if let Some(&[start, end]) = current_hidden {
+                if wrap_row >= end {
+                    current_hidden = hidden_iter.next();
+                    if let Some(&[new_start, new_end]) = current_hidden {
+                        wrap_row >= new_start && wrap_row < new_end
+                    } else {
+                        false
+                    }
+                } else {
+                    wrap_row >= start && wrap_row < end
+                }
+            } else {
+                false
+            };
+
+            if !is_hidden {
+                self.visible_wrap_rows.push(wrap_row);
+                self.wrap_row_to_display_row[wrap_row] = Some(display_row);
+                display_row += 1;
+            }
+        }
+
+        self.needs_rebuild = false;
+    }
+}

crates/ui/src/input/display_map/folding.rs

@@ -0,0 +1,96 @@
+use std::ops::Range;
+
+#[cfg(not(target_family = "wasm"))]
+use tree_sitter::Node;
+#[cfg(not(target_family = "wasm"))]
+pub use tree_sitter::Tree;
+
+#[cfg(target_family = "wasm")]
+/// Stub type for tree-sitter Tree on WASM (tree-sitter not available).
+pub struct Tree;
+
+#[cfg(not(target_family = "wasm"))]
+/// Minimum line span for a node to be considered foldable.
+const MIN_FOLD_LINES: usize = 2;
+
+/// A fold range representing a foldable code region.
+///
+/// The fold range spans from start_line to end_line (inclusive).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct FoldRange {
+    /// Start line (inclusive)
+    pub start_line: usize,
+    /// End line (inclusive)
+    pub end_line: usize,
+}
+
+impl FoldRange {
+    pub fn new(start_line: usize, end_line: usize) -> Self {
+        assert!(
+            start_line <= end_line,
+            "fold start_line must be <= end_line"
+        );
+        Self {
+            start_line,
+            end_line,
+        }
+    }
+}
+
+#[cfg(not(target_family = "wasm"))]
+/// Check if a named node qualifies as a fold candidate.
+///
+/// Uses a structural heuristic: any **named** node spanning ≥ MIN_FOLD_LINES
+/// is foldable. tree-sitter already parses code into semantic units (functions,
+/// classes, blocks, etc.), so named nodes naturally correspond to meaningful
+/// foldable regions across all languages without a per-language node-type list.
+fn is_foldable_node(node: &Node) -> bool {
+    let start = node.start_position().row;
+    let end = node.end_position().row;
+    end.saturating_sub(start) >= MIN_FOLD_LINES
+}
+
+#[cfg(not(target_family = "wasm"))]
+/// Extract fold ranges only within a byte range (for incremental updates after edits).
+///
+/// Skips subtrees entirely outside the range, making it O(nodes in range)
+/// instead of O(all nodes in tree).
+pub fn extract_fold_ranges_in_range(tree: &Tree, byte_range: Range<usize>) -> Vec<FoldRange> {
+    let mut ranges = Vec::new();
+    let root = tree.root_node();
+    let mut cursor = root.walk();
+    // Skip the root, it's not foldable. Use named_children to skip literal tokens.
+    for child in root.named_children(&mut cursor) {
+        collect_foldable_nodes_in_range(child, &byte_range, &mut ranges);
+    }
+
+    ranges.sort_by_key(|r| r.start_line);
+    ranges.dedup_by_key(|r| r.start_line);
+    ranges
+}
+
+#[cfg(not(target_family = "wasm"))]
+/// Recursively collect foldable nodes, skipping subtrees outside byte_range.
+fn collect_foldable_nodes_in_range(
+    node: Node,
+    byte_range: &Range<usize>,
+    ranges: &mut Vec<FoldRange>,
+) {
+    if node.end_byte() <= byte_range.start || node.start_byte() >= byte_range.end {
+        return;
+    }
+
+    if !is_foldable_node(&node) {
+        return;
+    }
+
+    ranges.push(FoldRange {
+        start_line: node.start_position().row,
+        end_line: node.end_position().row,
+    });
+
+    let mut cursor = node.walk();
+    for child in node.named_children(&mut cursor) {
+        collect_foldable_nodes_in_range(child, byte_range, ranges);
+    }
+}

crates/ui/src/input/display_map/mod.rs

@@ -0,0 +1,69 @@
+/// Display mapping system for Editor/Input.
+///
+/// This module implements a layered display mapping architecture:
+/// - **WrapMap**: Handles soft-wrapping (buffer → wrap rows)
+/// - **FoldMap**: Handles folding (wrap rows → display rows)
+/// - **DisplayMap**: Public facade for Editor/Input
+///
+/// The goal is to provide a clean, unified API where Editor only needs to know
+/// about `BufferPoint ↔ DisplayPoint` mapping, without worrying about internal wrap/fold complexity.
+mod display_map;
+mod fold_map;
+#[cfg(not(target_family = "wasm"))]
+mod folding;
+#[cfg(target_family = "wasm")]
+pub mod folding;
+mod text_wrapper;
+mod wrap_map;
+
+// Re-export public API
+// Re-export FoldRange and extract_fold_ranges
+pub use folding::FoldRange;
+
+pub use self::display_map::DisplayMap;
+pub(crate) use self::text_wrapper::LineLayout;
+
+/// Position in the buffer (logical text).
+///
+/// - `line`: 0-based logical line number (split by `\n`)
+/// - `col`: 0-based column offset (byte offset)
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct BufferPoint {
+    pub line: usize,
+    pub col: usize,
+}
+
+impl BufferPoint {
+    pub fn new(line: usize, col: usize) -> Self {
+        Self { line, col }
+    }
+}
+
+/// Position after soft-wrapping but before folding (internal).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub(super) struct WrapPoint {
+    pub row: usize,
+    pub col: usize,
+}
+
+impl WrapPoint {
+    pub fn new(row: usize, col: usize) -> Self {
+        Self { row, col }
+    }
+}
+
+/// Final display position (after soft-wrapping and folding).
+///
+/// - `row`: 0-based display row (final visible row)
+/// - `col`: 0-based display column
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct DisplayPoint {
+    pub row: usize,
+    pub col: usize,
+}
+
+impl DisplayPoint {
+    pub fn new(row: usize, col: usize) -> Self {
+        Self { row, col }
+    }
+}

crates/ui/src/input/display_map/text_wrapper.rs

@@ -0,0 +1,930 @@
+use std::ops::Range;
+use gpui::Half;
+
+use gpui::{
+    App, Font, LineFragment, Pixels, Point, ShapedLine, Size, TextAlign, Window, point, px,
+    size,
+};
+use ropey::Rope;
+use smallvec::SmallVec;
+
+use crate::input::{LastLayout, Point as TreeSitterPoint, RopeExt, WhitespaceIndicators};
+
+/// A line with soft wrapped lines info.
+#[derive(Debug, Clone)]
+pub(crate) struct LineItem {
+    /// The original line text, without end `\n`.
+    line: Rope,
+    /// The soft wrapped lines relative byte range (0..line.len) of this line (Include first line).
+    ///
+    /// Not contains the line end `\n`.
+    pub(crate) wrapped_lines: Vec<Range<usize>>,
+}
+
+impl LineItem {
+    /// Get the bytes length of this line.
+    #[inline]
+    pub(crate) fn len(&self) -> usize {
+        self.line.len()
+    }
+
+    /// Get number of soft wrapped lines of this line (include the first line).
+    #[inline]
+    pub(crate) fn lines_len(&self) -> usize {
+        self.wrapped_lines.len()
+    }
+}
+
+#[derive(Debug, Default)]
+pub(crate) struct LongestRow {
+    /// The 0-based row index.
+    pub row: usize,
+    /// The bytes length of the longest line.
+    pub len: usize,
+}
+
+/// Used to prepare the text with soft wrap to be get lines to displayed in the Editor.
+///
+/// After use lines to calculate the scroll size of the Editor.
+pub(crate) struct TextWrapper {
+    text: Rope,
+    /// Total wrapped lines (Inlucde the first line), value is start and end index of the line.
+    soft_lines: usize,
+    font: Font,
+    font_size: Pixels,
+    /// If is none, it means the text is not wrapped
+    wrap_width: Option<Pixels>,
+    /// The longest (row, bytes len) in characters, used to calculate the horizontal scroll width.
+    pub(crate) longest_row: LongestRow,
+    /// The lines by split \n
+    pub(crate) lines: Vec<LineItem>,
+
+    _initialized: bool,
+}
+
+#[allow(unused)]
+impl TextWrapper {
+    pub(crate) fn new(font: Font, font_size: Pixels, wrap_width: Option<Pixels>) -> Self {
+        Self {
+            text: Rope::new(),
+            font,
+            font_size,
+            wrap_width,
+            soft_lines: 0,
+            longest_row: LongestRow::default(),
+            lines: Vec::new(),
+            _initialized: false,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn set_default_text(&mut self, text: &Rope) {
+        self.text = text.clone();
+    }
+
+    /// Get reference to the rope text.
+    #[inline]
+    pub(crate) fn text(&self) -> &Rope {
+        &self.text
+    }
+
+    /// Get the total number of lines including wrapped lines.
+    #[inline]
+    pub(crate) fn len(&self) -> usize {
+        self.soft_lines
+    }
+
+    /// Get the line item by row index.
+    #[inline]
+    pub(crate) fn line(&self, row: usize) -> Option<&LineItem> {
+        self.lines.iter().skip(row).next()
+    }
+
+    pub(crate) fn set_wrap_width(&mut self, wrap_width: Option<Pixels>, cx: &mut App) {
+        if wrap_width == self.wrap_width {
+            return;
+        }
+
+        self.wrap_width = wrap_width;
+        self.update_all(&self.text.clone(), cx);
+    }
+
+    pub(crate) fn set_font(&mut self, font: Font, font_size: Pixels, cx: &mut App) {
+        if self.font.eq(&font) && self.font_size == font_size {
+            return;
+        }
+
+        self.font = font;
+        self.font_size = font_size;
+        self.update_all(&self.text.clone(), cx);
+    }
+
+    pub(crate) fn prepare_if_need(&mut self, text: &Rope, cx: &mut App) -> bool {
+        if self._initialized {
+            return false;
+        }
+        self._initialized = true;
+        self.update_all(text, cx);
+        true
+    }
+
+    /// Update the text wrapper and recalculate the wrapped lines.
+    ///
+    /// If the `text` is the same as the current text, do nothing.
+    ///
+    /// - `changed_text`: The text [`Rope`] that has changed.
+    /// - `range`: The `selected_range` before change.
+    /// - `new_text`: The inserted text.
+    /// - `force`: Whether to force the update, if false, the update will be skipped if the text is the same.
+    /// - `cx`: The application context.
+    pub(crate) fn update(
+        &mut self,
+        changed_text: &Rope,
+        range: &Range<usize>,
+        new_text: &Rope,
+        cx: &mut App,
+    ) {
+        let mut line_wrapper = cx
+            .text_system()
+            .line_wrapper(self.font.clone(), self.font_size);
+        self._update(
+            changed_text,
+            range,
+            new_text,
+            &mut |line_str, wrap_width| {
+                line_wrapper
+                    .wrap_line(&[LineFragment::text(line_str)], wrap_width)
+                    .collect()
+            },
+        );
+    }
+
+    fn _update<F>(
+        &mut self,
+        changed_text: &Rope,
+        range: &Range<usize>,
+        new_text: &Rope,
+        wrap_line: &mut F,
+    ) where
+        F: FnMut(&str, Pixels) -> Vec<gpui::Boundary>,
+    {
+        // Remove the old changed lines.
+        let start_row = self.text.offset_to_point(range.start).row;
+        let start_row = start_row.min(self.lines.len().saturating_sub(1));
+        let end_row = self.text.offset_to_point(range.end).row;
+        let end_row = end_row.min(self.lines.len().saturating_sub(1));
+        let rows_range = start_row..=end_row;
+
+        if rows_range.contains(&self.longest_row.row) {
+            self.longest_row = LongestRow::default();
+        }
+
+        let mut longest_row_ix = self.longest_row.row;
+        let mut longest_row_len = self.longest_row.len;
+
+        // To add the new lines.
+        let new_start_row = changed_text.offset_to_point(range.start).row;
+        let new_start_offset = changed_text.line_start_offset(new_start_row);
+        let new_end_row = changed_text
+            .offset_to_point(range.start + new_text.len())
+            .row;
+        let new_end_offset = changed_text.line_end_offset(new_end_row);
+        let new_range = new_start_offset..new_end_offset;
+
+        let mut new_lines = vec![];
+        let wrap_width = self.wrap_width;
+
+        // line not contains `\n`.
+        for (ix, line) in Rope::from(changed_text.slice(new_range))
+            .iter_lines()
+            .enumerate()
+        {
+            let line_str = line.to_string();
+            let mut wrapped_lines = vec![];
+            let mut prev_boundary_ix = 0;
+
+            if line_str.len() > longest_row_len {
+                longest_row_ix = new_start_row + ix;
+                longest_row_len = line_str.len();
+            }
+
+            // If wrap_width is Pixels::MAX, skip wrapping to disable word wrap
+            if let Some(wrap_width) = wrap_width {
+                // Here only have wrapped line, if there is no wrap meet, the `line_wraps` result will empty.
+                for boundary in wrap_line(&line_str, wrap_width) {
+                    wrapped_lines.push(prev_boundary_ix..boundary.ix);
+                    prev_boundary_ix = boundary.ix;
+                }
+            }
+
+            // Reset of the line
+            if !line_str[prev_boundary_ix..].is_empty() || prev_boundary_ix == 0 {
+                wrapped_lines.push(prev_boundary_ix..line.len());
+            }
+
+            new_lines.push(LineItem {
+                line: Rope::from(line),
+                wrapped_lines,
+            });
+        }
+
+        if self.lines.len() == 0 {
+            self.lines = new_lines;
+        } else {
+            self.lines.splice(rows_range, new_lines);
+        }
+
+        self.text = changed_text.clone();
+        self.soft_lines = self.lines.iter().map(|l| l.lines_len()).sum();
+        self.longest_row = LongestRow {
+            row: longest_row_ix,
+            len: longest_row_len,
+        }
+    }
+
+    /// Update the text wrapper and recalculate the wrapped lines.
+    ///
+    /// If the `text` is the same as the current text, do nothing.
+    fn update_all(&mut self, text: &Rope, cx: &mut App) {
+        self.update(text, &(0..text.len()), &text, cx);
+    }
+
+    /// Return display point (with soft wrap) from the given byte offset in the text.
+    ///
+    /// Panics if the `offset` is out of bounds.
+    pub(crate) fn offset_to_display_point(&self, offset: usize) -> WrapDisplayPoint {
+        let row = self.text.offset_to_point(offset).row;
+        let start = self.text.line_start_offset(row);
+        let line = &self.lines[row];
+
+        let mut wrapped_row = self
+            .lines
+            .iter()
+            .take(row)
+            .map(|l| l.lines_len())
+            .sum::<usize>();
+
+        let local_offset = offset.saturating_sub(start);
+        for (ix, range) in line.wrapped_lines.iter().enumerate() {
+            if range.contains(&local_offset) {
+                return WrapDisplayPoint::new(
+                    wrapped_row + ix,
+                    ix,
+                    local_offset.saturating_sub(range.start),
+                );
+            }
+        }
+
+        // Otherwise return the eof of the line.
+        let last_range = line.wrapped_lines.last().unwrap_or(&(0..0));
+        let ix = line.lines_len().saturating_sub(1);
+        return WrapDisplayPoint::new(wrapped_row + ix, ix, last_range.len());
+    }
+
+    /// Return byte offset in the text from the given display point (with soft wrap).
+    ///
+    /// Panics if the `point.row` is out of bounds.
+    pub(crate) fn display_point_to_offset(&self, point: WrapDisplayPoint) -> usize {
+        let mut wrapped_row = 0;
+        for (row, line) in self.lines.iter().enumerate() {
+            if wrapped_row + line.lines_len() > point.row {
+                let line_start = self.text.line_start_offset(row);
+                let local_row = point.row.saturating_sub(wrapped_row);
+                if let Some(range) = line.wrapped_lines.get(local_row) {
+                    return line_start + (range.start + point.column).min(range.end);
+                } else {
+                    // If not found, return the end of the line.
+                    return line_start + line.len();
+                }
+            }
+
+            wrapped_row += line.lines_len();
+        }
+
+        return self.text.len();
+    }
+
+    pub(crate) fn display_point_to_point(&self, point: WrapDisplayPoint) -> TreeSitterPoint {
+        let offset = self.display_point_to_offset(point);
+        self.text.offset_to_point(offset)
+    }
+
+    pub(crate) fn point_to_display_point(&self, point: TreeSitterPoint) -> WrapDisplayPoint {
+        let offset = self.text.point_to_offset(point);
+        self.offset_to_display_point(offset)
+    }
+}
+
+/// A display point within the soft-wrapped text.
+///
+/// This represents a position in the text after soft-wrapping,
+/// with an additional `local_row` field tracking the wrap line
+/// within the original buffer line.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct WrapDisplayPoint {
+    /// The 0-based soft wrapped row index in the text.
+    pub row: usize,
+    /// The 0-based row index in local line (include first line).
+    ///
+    /// This value only valid when return from [`TextWrapper::offset_to_display_point`], otherwise it will be ignored.
+    pub local_row: usize,
+    /// The 0-based column byte index in the display line (with soft wrap).
+    pub column: usize,
+}
+
+impl WrapDisplayPoint {
+    pub fn new(row: usize, local_row: usize, column: usize) -> Self {
+        Self {
+            row,
+            local_row,
+            column,
+        }
+    }
+}
+
+/// The layout info of a line with soft wrapped lines.
+pub(crate) struct LineLayout {
+    /// Total bytes length of this line.
+    len: usize,
+    /// The soft wrapped lines of this line (Include the first line).
+    pub(crate) wrapped_lines: SmallVec<[ShapedLine; 1]>,
+    pub(crate) longest_width: Pixels,
+    pub(crate) whitespace_indicators: Option<WhitespaceIndicators>,
+    /// Whitespace indicators: (line_index, x_position, is_tab)
+    pub(crate) whitespace_chars: Vec<(usize, Pixels, bool)>,
+}
+
+impl LineLayout {
+    pub(crate) fn new() -> Self {
+        Self {
+            len: 0,
+            longest_width: px(0.),
+            wrapped_lines: SmallVec::new(),
+            whitespace_chars: Vec::new(),
+            whitespace_indicators: None,
+        }
+    }
+
+    pub(crate) fn lines(mut self, wrapped_lines: SmallVec<[ShapedLine; 1]>) -> Self {
+        self.set_wrapped_lines(wrapped_lines);
+        self
+    }
+
+    pub(crate) fn set_wrapped_lines(&mut self, wrapped_lines: SmallVec<[ShapedLine; 1]>) {
+        self.len = wrapped_lines.iter().map(|l| l.len).sum();
+        let width = wrapped_lines
+            .iter()
+            .map(|l| l.width)
+            .max()
+            .unwrap_or_default();
+        self.longest_width = width;
+        self.wrapped_lines = wrapped_lines;
+    }
+
+    pub(crate) fn with_whitespaces(mut self, indicators: Option<WhitespaceIndicators>) -> Self {
+        self.whitespace_indicators = indicators;
+        let Some(indicators) = self.whitespace_indicators.as_ref() else {
+            return self;
+        };
+
+        let space_indicator_offset = indicators.space.width.half();
+
+        for (line_index, wrapped_line) in self.wrapped_lines.iter().enumerate() {
+            for (relative_offset, c) in wrapped_line.text.char_indices() {
+                if matches!(c, ' ' | '\t') {
+                    let is_tab = c == '\t';
+                    let start_x = wrapped_line.x_for_index(relative_offset);
+                    let end_x = wrapped_line.x_for_index(relative_offset + c.len_utf8());
+                    // Center the indicator in the actual character's space
+                    let x_position = if c == ' ' {
+                        (start_x + end_x).half() - space_indicator_offset
+                    } else {
+                        start_x
+                    };
+
+                    self.whitespace_chars.push((line_index, x_position, is_tab));
+                }
+            }
+        }
+        self
+    }
+
+    #[inline]
+    pub(crate) fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Get the position (x, y) for the given index in this line layout.
+    ///
+    /// - The `offset` is a local byte index in this line layout.
+    /// - When `line_end_affinity` is true, an offset at a soft wrap boundary is placed at
+    ///   the end of the current visual line rather than the start of the next one.
+    /// - The return value is relative to the top-left corner of this line layout, start from (0, 0)
+    pub(crate) fn position_for_index(
+        &self,
+        offset: usize,
+        last_layout: &LastLayout,
+        line_end_affinity: bool,
+    ) -> Option<Point<Pixels>> {
+        let mut acc_len = 0;
+        let mut offset_y = px(0.);
+
+        let x_offset = last_layout.alignment_offset(self.longest_width);
+
+        for (i, line) in self.wrapped_lines.iter().enumerate() {
+            let is_last = i + 1 == self.wrapped_lines.len();
+
+            let matches = if line.len == 0 {
+                // Empty visual lines still own their boundary offset.
+                offset == acc_len
+            } else if is_last || line_end_affinity {
+                // Inclusive: cursor can sit at end of this visual line.
+                offset >= acc_len && offset <= acc_len + line.len
+            } else {
+                // Exclusive: boundary offset belongs to the next visual line.
+                offset >= acc_len && offset < acc_len + line.len
+            };
+
+            if matches {
+                let x = line.x_for_index(offset.saturating_sub(acc_len)) + x_offset;
+                return Some(point(x, offset_y));
+            }
+
+            // Always advance by actual line length. The last line gets +1 so the
+            // cursor can be placed after the final character.
+            acc_len += if is_last { line.len + 1 } else { line.len };
+            offset_y += last_layout.line_height;
+        }
+
+        None
+    }
+
+    /// Get the closest index for the given x in this line layout.
+    pub(crate) fn closest_index_for_x(&self, x: Pixels, last_layout: &LastLayout) -> usize {
+        let mut acc_len = 0;
+        let x_offset = last_layout.alignment_offset(self.longest_width);
+        let x = x - x_offset;
+
+        for (i, line) in self.wrapped_lines.iter().enumerate() {
+            let is_last = i + 1 == self.wrapped_lines.len();
+            if x <= line.width {
+                let mut ix = line.closest_index_for_x(x);
+                if !is_last && ix == line.text.len() {
+                    // For soft wrap line, we can't put the cursor at the end of the line.
+                    let c_len = line.text.chars().last().map(|c| c.len_utf8()).unwrap_or(0);
+                    ix = ix.saturating_sub(c_len);
+                }
+
+                return acc_len + ix;
+            }
+            acc_len += line.text.len();
+        }
+
+        acc_len
+    }
+
+    /// Get the index for the given position (x, y) in this line layout.
+    ///
+    /// The `pos` is relative to the top-left corner of this line layout, start from (0, 0)
+    /// The return value is a local byte index in this line layout, start from 0.
+    pub(crate) fn closest_index_for_position(
+        &self,
+        pos: Point<Pixels>,
+        last_layout: &LastLayout,
+    ) -> Option<usize> {
+        let mut offset = 0;
+        let mut line_top = px(0.);
+        let x_offset = last_layout.alignment_offset(self.longest_width);
+        for (i, line) in self.wrapped_lines.iter().enumerate() {
+            let is_last = i + 1 == self.wrapped_lines.len();
+            let line_bottom = line_top + last_layout.line_height;
+            if pos.y >= line_top && pos.y < line_bottom {
+                let mut ix = line.closest_index_for_x(pos.x - x_offset);
+                if !is_last && ix == line.text.len() {
+                    // For soft wrap line, we can't put the cursor at the end of the line.
+                    let c_len = line.text.chars().last().map(|c| c.len_utf8()).unwrap_or(0);
+                    ix = ix.saturating_sub(c_len);
+                }
+                return Some(offset + ix);
+            }
+
+            offset += line.text.len();
+            line_top = line_bottom;
+        }
+
+        None
+    }
+
+    pub(crate) fn index_for_position(
+        &self,
+        pos: Point<Pixels>,
+        last_layout: &LastLayout,
+    ) -> Option<usize> {
+        let mut offset = 0;
+        let mut line_top = px(0.);
+        let x_offset = last_layout.alignment_offset(self.longest_width);
+        for line in self.wrapped_lines.iter() {
+            let line_bottom = line_top + last_layout.line_height;
+            if pos.y >= line_top && pos.y < line_bottom {
+                let ix = line.index_for_x(pos.x - x_offset)?;
+                return Some(offset + ix);
+            }
+
+            offset += line.text.len();
+            line_top = line_bottom;
+        }
+
+        None
+    }
+
+    pub(crate) fn size(&self, line_height: Pixels) -> Size<Pixels> {
+        size(self.longest_width, self.wrapped_lines.len() * line_height)
+    }
+
+    pub(crate) fn paint(
+        &self,
+        pos: Point<Pixels>,
+        line_height: Pixels,
+        text_align: TextAlign,
+        align_width: Option<Pixels>,
+        window: &mut Window,
+        cx: &mut App,
+    ) {
+        for (ix, line) in self.wrapped_lines.iter().enumerate() {
+            _ = line.paint(
+                pos + point(px(0.), ix * line_height),
+                line_height,
+                text_align,
+                align_width,
+                window,
+                cx,
+            );
+        }
+
+        // Paint whitespace indicators
+        if let Some(indicators) = self.whitespace_indicators.as_ref() {
+            for (line_index, x_position, is_tab) in &self.whitespace_chars {
+                let invisible = if *is_tab {
+                    indicators.tab.clone()
+                } else {
+                    indicators.space.clone()
+                };
+
+                let origin = point(
+                    pos.x + *x_position,
+                    pos.y + *line_index as f32 * line_height,
+                );
+
+                _ = invisible.paint(origin, line_height, text_align, align_width, window, cx);
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::rc::Rc;
+
+    use gpui::{Boundary, FontFeatures, FontStyle, FontWeight, px};
+
+    #[test]
+    fn test_update() {
+        let font = gpui::Font {
+            family: "Arial".into(),
+            weight: FontWeight::default(),
+            style: FontStyle::Normal,
+            features: FontFeatures::default(),
+            fallbacks: None,
+        };
+
+        let mut wrapper = TextWrapper::new(font, px(14.), None);
+        let mut text = Rope::from(
+            "Hello, 世界!\r\nThis is second line.\nThis is third line.\n这里是第 4 行。",
+        );
+
+        fn fake_wrap_line(_line: &str, _wrap_width: Pixels) -> Vec<Boundary> {
+            vec![]
+        }
+
+        #[track_caller]
+        fn assert_wrapper_lines(text: &Rope, wrapper: &TextWrapper, expected_lines: &[&[&str]]) {
+            let mut actual_lines = vec![];
+            let mut offset = 0;
+            for line in wrapper.lines.iter() {
+                actual_lines.push(
+                    line.wrapped_lines
+                        .iter()
+                        .map(|range| text.slice(offset + range.start..offset + range.end))
+                        .collect::<Vec<_>>(),
+                );
+                // +1 \n
+                offset += line.len() + 1;
+            }
+            assert_eq!(actual_lines, expected_lines);
+        }
+
+        wrapper._update(&text, &(0..text.len()), &text, &mut fake_wrap_line);
+        assert_eq!(wrapper.lines.len(), 4);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["Hello, 世界!\r"],
+                &["This is second line."],
+                &["This is third line."],
+                &["这里是第 4 行。"],
+            ],
+        );
+
+        // Add a new text to end
+        let range = text.len()..text.len();
+        let new_text = "New text";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "Hello, 世界!\r\nThis is second line.\nThis is third line.\n这里是第 4 行。New text"
+        );
+        assert_eq!(wrapper.lines.len(), 4);
+        assert_eq!(wrapper.lines.len(), 4);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["Hello, 世界!\r"],
+                &["This is second line."],
+                &["This is third line."],
+                &["这里是第 4 行。New text"],
+            ],
+        );
+
+        // Replace first line `Hello` to `AAA`
+        let range = 0..5;
+        let new_text = "AAA";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "AAA, 世界!\r\nThis is second line.\nThis is third line.\n这里是第 4 行。New text"
+        );
+        assert_eq!(wrapper.lines.len(), 4);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["AAA, 世界!\r"],
+                &["This is second line."],
+                &["This is third line."],
+                &["这里是第 4 行。New text"],
+            ],
+        );
+
+        // Remove the second line
+        let start_offset = text.line_start_offset(1);
+        let end_offset = text.line_end_offset(1);
+        let range = start_offset..end_offset + 1;
+        text.replace(range.clone(), "");
+        wrapper._update(&text, &range, &Rope::from(""), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "AAA, 世界!\r\nThis is third line.\n这里是第 4 行。New text"
+        );
+        assert_eq!(wrapper.lines.len(), 3);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["AAA, 世界!\r"],
+                &["This is third line."],
+                &["这里是第 4 行。New text"],
+            ],
+        );
+
+        // Replace the first 2 lines to "This is a new line."
+        let range = text.line_start_offset(0)..text.line_end_offset(1) + 1;
+        let new_text = "This is a new line.\nThis is new line 2.\n";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "This is a new line.\nThis is new line 2.\n这里是第 4 行。New text"
+        );
+        assert_eq!(wrapper.lines.len(), 3);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["This is a new line."],
+                &["This is new line 2."],
+                &["这里是第 4 行。New text"],
+            ],
+        );
+
+        // Add a new line at the end
+        let range = text.len()..text.len();
+        let new_text = "\nThis is a new line at the end.";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "This is a new line.\nThis is new line 2.\n这里是第 4 行。New text\nThis is a new line at the end."
+        );
+        assert_eq!(wrapper.lines.len(), 4);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["This is a new line."],
+                &["This is new line 2."],
+                &["这里是第 4 行。New text"],
+                &["This is a new line at the end."],
+            ],
+        );
+
+        // Add a new line at the beginning
+        let range = 0..0;
+        let new_text = "This is a new line at the beginning.\n";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "This is a new line at the beginning.\nThis is a new line.\nThis is new line 2.\n这里是第 4 行。New text\nThis is a new line at the end."
+        );
+        assert_eq!(wrapper.lines.len(), 5);
+        assert_wrapper_lines(
+            &text,
+            &wrapper,
+            &[
+                &["This is a new line at the beginning."],
+                &["This is a new line."],
+                &["This is new line 2."],
+                &["这里是第 4 行。New text"],
+                &["This is a new line at the end."],
+            ],
+        );
+
+        // Remove all to at least one line in `lines`.
+        let range = 0..text.len();
+        let new_text = "";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &Rope::from(new_text), &mut fake_wrap_line);
+        assert_eq!(text.to_string(), "");
+        assert_eq!(wrapper.lines.len(), 1);
+        assert_eq!(wrapper.lines[0].wrapped_lines, vec![0..0]);
+
+        // Test update_all
+        let range = 0..text.len();
+        let new_text = "This is a full text.\nThis is a second line.";
+        text.replace(range.clone(), new_text);
+        wrapper._update(&text, &range, &text, &mut fake_wrap_line);
+        assert_eq!(
+            text.to_string(),
+            "This is a full text.\nThis is a second line."
+        );
+        assert_eq!(wrapper.lines.len(), 2);
+    }
+
+    #[test]
+    fn test_line_layout() {
+        let mut line_layout = LineLayout::new();
+
+        let line1 = ShapedLine::default().with_len(100);
+        let line2 = ShapedLine::default().with_len(50);
+        let wrapped_lines = smallvec::smallvec![line1, line2];
+        line_layout.set_wrapped_lines(wrapped_lines);
+        assert_eq!(line_layout.len(), 150);
+        assert_eq!(line_layout.wrapped_lines.len(), 2);
+    }
+
+    #[test]
+    fn test_position_for_index_prefers_first_leading_empty_visual_line() {
+        let mut line_layout = LineLayout::new();
+        line_layout.set_wrapped_lines(smallvec::smallvec![
+            ShapedLine::default(),
+            ShapedLine::default(),
+            ShapedLine::default().with_len(3),
+        ]);
+
+        let last_layout = LastLayout {
+            visible_range: 0..1,
+            visible_buffer_lines: vec![0],
+            visible_line_byte_offsets: vec![0],
+            visible_top: px(0.),
+            visible_range_offset: 0..0,
+            lines: Rc::new(vec![]),
+            line_height: px(20.),
+            wrap_width: None,
+            line_number_width: px(0.),
+            cursor_bounds: None,
+            text_align: TextAlign::Left,
+            content_width: px(0.),
+        };
+
+        assert_eq!(
+            line_layout.position_for_index(0, &last_layout, false),
+            Some(point(px(0.), px(0.)))
+        );
+    }
+
+    #[test]
+    fn test_offset_to_display_point() {
+        let font = gpui::Font {
+            family: "Arial".into(),
+            weight: FontWeight::default(),
+            style: FontStyle::Normal,
+            features: FontFeatures::default(),
+            fallbacks: None,
+        };
+
+        let mut wrapper = TextWrapper::new(font, px(14.), None);
+        wrapper.text = Rope::from(
+            "Hello, 世界!\r\nThis is second line.\nThis is third line.\n这里是第 4 行。",
+        );
+        wrapper.lines = vec![
+            // range: 0..15
+            LineItem {
+                line: Rope::from("Hello, 世界!\r"),
+                wrapped_lines: vec![0..15],
+            },
+            // range: 16..36
+            LineItem {
+                line: Rope::from("This is second line."),
+                wrapped_lines: vec![0..10, 10..20],
+            },
+            // range: 37..56
+            LineItem {
+                line: Rope::from("This is third line."),
+                wrapped_lines: vec![0..9, 9..15, 15..20],
+            },
+            // range: 57..79
+            LineItem {
+                line: Rope::from("这里是第 4 行。"),
+                wrapped_lines: vec![0..22],
+            },
+        ];
+
+        assert_eq!(
+            wrapper.offset_to_display_point(12),
+            WrapDisplayPoint::new(0, 0, 12)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(15),
+            WrapDisplayPoint::new(0, 0, 15)
+        );
+
+        assert_eq!(
+            wrapper.offset_to_display_point(16),
+            WrapDisplayPoint::new(1, 0, 0)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(21),
+            WrapDisplayPoint::new(1, 0, 5)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(27),
+            WrapDisplayPoint::new(2, 1, 1)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(37),
+            WrapDisplayPoint::new(3, 0, 0)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(54),
+            WrapDisplayPoint::new(5, 2, 2)
+        );
+        assert_eq!(
+            wrapper.offset_to_display_point(59),
+            WrapDisplayPoint::new(6, 0, 2)
+        );
+
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(6, 0, 2)),
+            59
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(5, 2, 2)),
+            54
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(3, 0, 0)),
+            37
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(2, 1, 1)),
+            27
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(1, 0, 5)),
+            21
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(1, 0, 0)),
+            16
+        );
+        assert_eq!(
+            wrapper.display_point_to_offset(WrapDisplayPoint::new(0, 0, 15)),
+            15
+        );
+    }
+}

crates/ui/src/input/display_map/wrap_map.rs

@@ -0,0 +1,222 @@
+/// WrapMap: Soft-wrapping layer (Buffer → Wrap rows).
+///
+/// This module wraps the existing TextWrapper and provides:
+/// - BufferPoint ↔ WrapPoint mapping
+/// - Efficient buffer_line → wrap_row queries via prefix sum cache
+/// - Incremental updates when text or layout changes
+use std::ops::Range;
+
+use gpui::{App, Font, Pixels};
+use ropey::Rope;
+
+use super::fold_map::FoldMap;
+use super::text_wrapper::{LineItem, TextWrapper, WrapDisplayPoint};
+use super::{BufferPoint, WrapPoint};
+use crate::input::rope_ext::RopeExt;
+
+/// WrapMap manages soft-wrapping and provides buffer ↔ wrap coordinate mapping.
+pub struct WrapMap {
+    /// The underlying text wrapper (reuses existing implementation)
+    wrapper: TextWrapper,
+
+    /// Prefix sum cache: buffer_line_starts[line] = first wrap_row for buffer line `line`
+    /// This allows O(1) lookup of buffer_line → wrap_row
+    buffer_line_starts: Vec<usize>,
+
+    /// Cached line count from last rebuild
+    cached_line_count: usize,
+
+    /// Cached total wrap row count from last rebuild.
+    /// Used together with `cached_line_count` to detect if the cache is stale.
+    /// When soft wrap changes a line's wrap count without changing buffer line count,
+    /// this catches the staleness.
+    cached_wrap_row_count: usize,
+}
+
+impl WrapMap {
+    pub fn new(font: Font, font_size: Pixels, wrap_width: Option<Pixels>) -> Self {
+        Self {
+            wrapper: TextWrapper::new(font, font_size, wrap_width),
+            buffer_line_starts: Vec::new(),
+            cached_line_count: 0,
+            cached_wrap_row_count: 0,
+        }
+    }
+
+    /// Get total number of wrap rows (visual rows after soft-wrapping)
+    #[inline]
+    pub fn wrap_row_count(&self) -> usize {
+        self.wrapper.len()
+    }
+
+    /// Get total number of buffer lines (logical lines)
+    #[inline]
+    pub fn buffer_line_count(&self) -> usize {
+        self.wrapper.lines.len()
+    }
+
+    /// Convert buffer position to wrap position
+    pub(super) fn buffer_pos_to_wrap_pos(&self, pos: BufferPoint) -> WrapPoint {
+        let BufferPoint { line, col } = pos;
+
+        // Clamp to valid range
+        let line = line.min(self.buffer_line_count().saturating_sub(1));
+        let line_item = self.wrapper.lines.get(line);
+
+        let col = if let Some(line_item) = line_item {
+            col.min(line_item.len())
+        } else {
+            0
+        };
+
+        // Calculate offset in rope
+        let line_start_offset = self.wrapper.text().line_start_offset(line);
+        let offset = line_start_offset + col;
+
+        // Use TextWrapper's existing conversion
+        let display_point = self.wrapper.offset_to_display_point(offset);
+
+        WrapPoint::new(display_point.row, display_point.column)
+    }
+
+    /// Convert wrap position to buffer position
+    pub(super) fn wrap_pos_to_buffer_pos(&self, pos: WrapPoint) -> BufferPoint {
+        let WrapPoint { row, col } = pos;
+
+        // Clamp wrap_row to valid range
+        let row = row.min(self.wrap_row_count().saturating_sub(1));
+
+        // Use TextWrapper's existing conversion
+        let display_point = WrapDisplayPoint::new(row, 0, col);
+        let offset = self.wrapper.display_point_to_offset(display_point);
+
+        // Convert offset to buffer position
+        let point = self.wrapper.text().offset_to_point(offset);
+        let line_start = self.wrapper.text().line_start_offset(point.row);
+        let col = offset.saturating_sub(line_start);
+
+        BufferPoint::new(point.row, col)
+    }
+
+    /// Get the buffer line for a given wrap row
+    pub fn wrap_row_to_buffer_line(&self, wrap_row: usize) -> usize {
+        if wrap_row >= self.wrap_row_count() {
+            return self.buffer_line_count().saturating_sub(1);
+        }
+
+        // Binary search in prefix sum cache
+        match self.buffer_line_starts.binary_search(&wrap_row) {
+            Ok(line) => line,
+            Err(insert_pos) => insert_pos.saturating_sub(1),
+        }
+    }
+
+    /// Get the first wrap row for a given buffer line
+    pub fn buffer_line_to_first_wrap_row(&self, line: usize) -> usize {
+        if line >= self.buffer_line_starts.len() {
+            return self.wrap_row_count();
+        }
+        self.buffer_line_starts[line]
+    }
+
+    /// Get the wrap row range for a buffer line: [start, end)
+    pub fn buffer_line_to_wrap_row_range(&self, line: usize) -> Range<usize> {
+        let start = self.buffer_line_to_first_wrap_row(line);
+        let end = if line + 1 < self.buffer_line_starts.len() {
+            self.buffer_line_starts[line + 1]
+        } else {
+            self.wrap_row_count()
+        };
+        start..end
+    }
+
+    /// Update text (incremental or full)
+    pub fn on_text_changed(
+        &mut self,
+        changed_text: &Rope,
+        range: &Range<usize>,
+        new_text: &Rope,
+        cx: &mut App,
+    ) {
+        self.wrapper.update(changed_text, range, new_text, cx);
+        self.rebuild_cache();
+    }
+
+    /// Update layout parameters (wrap width or font)
+    pub fn on_layout_changed(&mut self, wrap_width: Option<Pixels>, cx: &mut App) {
+        self.wrapper.set_wrap_width(wrap_width, cx);
+        self.rebuild_cache();
+    }
+
+    /// Set font parameters
+    pub fn set_font(&mut self, font: Font, font_size: Pixels, cx: &mut App) {
+        self.wrapper.set_font(font, font_size, cx);
+        self.rebuild_cache();
+    }
+
+    /// Ensure text is prepared (initializes wrapper if needed)
+    pub fn ensure_text_prepared(&mut self, text: &Rope, cx: &mut App) -> bool {
+        let did_initialize = self.wrapper.prepare_if_need(text, cx);
+        if did_initialize {
+            self.rebuild_cache();
+        }
+        did_initialize
+    }
+
+    /// Initialize with text
+    pub fn set_text(&mut self, text: &Rope, cx: &mut App) {
+        self.wrapper.set_default_text(text);
+        self.wrapper.prepare_if_need(text, cx);
+        self.rebuild_cache();
+    }
+
+    /// Rebuild the prefix sum cache: buffer_line_starts
+    fn rebuild_cache(&mut self) {
+        let line_count = self.wrapper.lines.len();
+        let wrap_row_count = self.wrapper.len();
+
+        // Skip if nothing changed: both buffer line count and total wrap row count must match.
+        // Checking wrap_row_count is essential because soft-wrap can change the number of
+        // wrap rows per line without changing the buffer line count.
+        if line_count == self.cached_line_count
+            && wrap_row_count == self.cached_wrap_row_count
+            && !self.buffer_line_starts.is_empty()
+        {
+            return;
+        }
+
+        self.buffer_line_starts.clear();
+
+        let mut wrap_row = 0;
+        for line_item in &self.wrapper.lines {
+            self.buffer_line_starts.push(wrap_row);
+            wrap_row += line_item.lines_len();
+        }
+
+        self.cached_line_count = line_count;
+        self.cached_wrap_row_count = wrap_row_count;
+    }
+
+    /// Get access to the underlying wrapper (for rendering/hit-testing)
+    pub(crate) fn wrapper(&self) -> &TextWrapper {
+        &self.wrapper
+    }
+
+    /// Get access to line items (for rendering)
+    pub(crate) fn lines(&self) -> &[LineItem] {
+        &self.wrapper.lines
+    }
+
+    /// Get the rope text
+    pub fn text(&self) -> &Rope {
+        self.wrapper.text()
+    }
+
+    /// Calculate how many wrap rows of a buffer line are visible (not folded)
+    pub fn visible_wrap_row_count_for_line(&self, line: usize, fold_map: &FoldMap) -> usize {
+        let wrap_range = self.buffer_line_to_wrap_row_range(line);
+        wrap_range
+            .filter(|&wr| fold_map.wrap_row_to_display_row(wr).is_some())
+            .count()
+    }
+}