5 files changed, 132 insertions, 56 deletions

diff --git a/helix-core/src/movement.rs b/helix-core/src/movement.rs
index 21e97ae8..01bec47a 100644
--- a/helix-core/src/movement.rs
+++ b/helix-core/src/movement.rs
@@ -7,9 +7,8 @@ use crate::{
     coords_at_pos,
     graphemes::{
         next_grapheme_boundary, nth_next_grapheme_boundary, nth_prev_grapheme_boundary,
-        prev_grapheme_boundary, RopeGraphemes,
+        prev_grapheme_boundary,
     },
-    line_ending::line_without_line_ending,
     pos_at_coords, Position, Range, RopeSlice,
 };
 
@@ -85,10 +84,8 @@ pub fn move_vertically(
         } else {
             (row + count).min(slice.len_lines().saturating_sub(1))
         };
-        let max_col = RopeGraphemes::new(line_without_line_ending(&slice, new_row)).count();
-        let new_col = col.max(horiz as usize).min(max_col);
-
-        pos_at_coords(slice, Position::new(new_row, new_col))
+        let new_col = col.max(horiz as usize);
+        pos_at_coords(slice, Position::new(new_row, new_col), true)
     };
 
     // Compute the new range according to the type of movement.
@@ -365,7 +362,7 @@ mod test {
     fn test_vertical_move() {
         let text = Rope::from("abcd\nefg\nwrs");
         let slice = text.slice(..);
-        let pos = pos_at_coords(slice, (0, 4).into());
+        let pos = pos_at_coords(slice, (0, 4).into(), true);
 
         let range = Range::new(pos, pos);
         assert_eq!(
@@ -381,7 +378,7 @@ mod test {
     fn horizontal_moves_through_single_line_text() {
         let text = Rope::from(SINGLE_LINE_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
 
         let mut range = Range::point(position);
 
@@ -404,7 +401,7 @@ mod test {
     fn horizontal_moves_through_multiline_text() {
         let text = Rope::from(MULTILINE_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
 
         let mut range = Range::point(position);
 
@@ -431,7 +428,7 @@ mod test {
     fn selection_extending_moves_in_single_line_text() {
         let text = Rope::from(SINGLE_LINE_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
 
         let mut range = Range::point(position);
         let original_anchor = range.anchor;
@@ -452,7 +449,7 @@ mod test {
     fn vertical_moves_in_single_column() {
         let text = Rope::from(MULTILINE_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
         let mut range = Range::point(position);
         let moves_and_expected_coordinates = IntoIter::new([
             ((Direction::Forward, 1usize), (1, 0)),
@@ -477,7 +474,7 @@ mod test {
     fn vertical_moves_jumping_column() {
         let text = Rope::from(MULTILINE_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
         let mut range = Range::point(position);
 
         enum Axis {
@@ -510,10 +507,10 @@ mod test {
     }
 
     #[test]
-    fn multibyte_character_column_jumps() {
+    fn multibyte_character_wide_column_jumps() {
         let text = Rope::from(MULTIBYTE_CHARACTER_SAMPLE);
         let slice = text.slice(..);
-        let position = pos_at_coords(slice, (0, 0).into());
+        let position = pos_at_coords(slice, (0, 0).into(), true);
         let mut range = Range::point(position);
 
         // FIXME: The behaviour captured in this test diverges from both Kakoune and Vim. These
@@ -524,10 +521,16 @@ mod test {
             V,
         }
         let moves_and_expected_coordinates = IntoIter::new([
-            // Places cursor at the fourth kana
-            ((Axis::H, Direction::Forward, 4), (0, 4)),
-            // Descent places cursor at the fourth character.
-            ((Axis::V, Direction::Forward, 1usize), (1, 4)),
+            // Places cursor at the fourth kana (each of which are double-wide,
+            // so the visual column is 8).
+            ((Axis::H, Direction::Forward, 4), (0, 8)),
+            // Descent places cursor at the 8th character.
+            ((Axis::V, Direction::Forward, 1usize), (1, 8)),
+            // Moving back a single-width character.
+            ((Axis::H, Direction::Backward, 1usize), (1, 7)),
+            // Jumping back up into the middle of a double-width character shifts
+            // the column to the start of that character.
+            ((Axis::V, Direction::Backward, 1usize), (0, 6)),
         ]);
 
         for ((axis, direction, amount), coordinates) in moves_and_expected_coordinates {
diff --git a/helix-core/src/position.rs b/helix-core/src/position.rs
index c4e8c9d6..15627687 100644
--- a/helix-core/src/position.rs
+++ b/helix-core/src/position.rs
@@ -1,6 +1,9 @@
+use std::borrow::Cow;
+
 use crate::{
     chars::char_is_line_ending,
-    graphemes::{nth_next_grapheme_boundary, RopeGraphemes},
+    graphemes::{ensure_grapheme_boundary_prev, grapheme_width, RopeGraphemes},
+    line_ending::line_end_char_index,
     RopeSlice,
 };
 
@@ -52,23 +55,58 @@ impl From<Position> for tree_sitter::Point {
     }
 }
 /// Convert a character index to (line, column) coordinates.
+///
+/// TODO: this should be split into two methods: one for visual
+/// row/column, and one for "objective" row/column (possibly with
+/// the column specified in `char`s).  The former would be used
+/// for cursor movement, and the latter would be used for e.g. the
+/// row:column display in the status line.
 pub fn coords_at_pos(text: RopeSlice, pos: usize) -> Position {
-    // TODO: this isn't correct.  This needs to work in terms of
-    // visual horizontal position, not graphemes.
     let line = text.char_to_line(pos);
+
     let line_start = text.line_to_char(line);
-    let col = RopeGraphemes::new(text.slice(line_start..pos)).count();
+    let pos = ensure_grapheme_boundary_prev(text, pos);
+    let col = RopeGraphemes::new(text.slice(line_start..pos))
+        .map(|g| {
+            let g: Cow<str> = g.into();
+            grapheme_width(&g)
+        })
+        .sum();
+
     Position::new(line, col)
 }
 
 /// Convert (line, column) coordinates to a character index.
-pub fn pos_at_coords(text: RopeSlice, coords: Position) -> usize {
-    // TODO: this isn't correct.  This needs to work in terms of
-    // visual horizontal position, not graphemes.
+///
+/// `is_1_width` specifies whether the position should be treated
+/// as a block cursor or not.  This effects how line-ends are handled.
+/// `false` corresponds to properly round-tripping with `coords_at_pos()`,
+/// whereas `true` will ensure that block cursors don't jump off the
+/// end of the line.
+pub fn pos_at_coords(text: RopeSlice, coords: Position, is_1_width: bool) -> usize {
     let Position { row, col } = coords;
     let line_start = text.line_to_char(row);
-    // line_start + col
-    nth_next_grapheme_boundary(text, line_start, col)
+    let line_end = if is_1_width {
+        line_end_char_index(&text, row)
+    } else {
+        text.line_to_char((row + 1).min(text.len_lines()))
+    };
+
+    let mut prev_col = 0;
+    let mut col_char_offset = 0;
+    for g in RopeGraphemes::new(text.slice(line_start..line_end)) {
+        let g: Cow<str> = g.into();
+        let next_col = prev_col + grapheme_width(&g);
+
+        if next_col > col {
+            break;
+        }
+
+        prev_col = next_col;
+        col_char_offset += g.chars().count();
+    }
+
+    line_start + col_char_offset
 }
 
 #[cfg(test)]
@@ -84,13 +122,24 @@ mod test {
 
     #[test]
     fn test_coords_at_pos() {
-        // let text = Rope::from("ḧëḷḷö\nẅöṛḷḋ");
-        // let slice = text.slice(..);
-        // assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
-        // assert_eq!(coords_at_pos(slice, 5), (0, 5).into()); // position on \n
-        // assert_eq!(coords_at_pos(slice, 6), (1, 0).into()); // position on w
-        // assert_eq!(coords_at_pos(slice, 7), (1, 1).into()); // position on o
-        // assert_eq!(coords_at_pos(slice, 10), (1, 4).into()); // position on d
+        let text = Rope::from("ḧëḷḷö\nẅöṛḷḋ");
+        let slice = text.slice(..);
+        assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
+        assert_eq!(coords_at_pos(slice, 5), (0, 5).into()); // position on \n
+        assert_eq!(coords_at_pos(slice, 6), (1, 0).into()); // position on w
+        assert_eq!(coords_at_pos(slice, 7), (1, 1).into()); // position on o
+        assert_eq!(coords_at_pos(slice, 10), (1, 4).into()); // position on d
+
+        // Test with wide characters.
+        let text = Rope::from("今日はいい\n");
+        let slice = text.slice(..);
+        assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
+        assert_eq!(coords_at_pos(slice, 1), (0, 2).into());
+        assert_eq!(coords_at_pos(slice, 2), (0, 4).into());
+        assert_eq!(coords_at_pos(slice, 3), (0, 6).into());
+        assert_eq!(coords_at_pos(slice, 4), (0, 8).into());
+        assert_eq!(coords_at_pos(slice, 5), (0, 10).into());
+        assert_eq!(coords_at_pos(slice, 6), (1, 0).into());
 
         // test with grapheme clusters
         let text = Rope::from("a̐éö̲\r\n");
@@ -99,40 +148,64 @@ mod test {
         assert_eq!(coords_at_pos(slice, 2), (0, 1).into());
         assert_eq!(coords_at_pos(slice, 4), (0, 2).into());
         assert_eq!(coords_at_pos(slice, 7), (0, 3).into());
+        assert_eq!(coords_at_pos(slice, 9), (1, 0).into());
 
-        let text = Rope::from("किमपि");
+        let text = Rope::from("किमपि\n");
         let slice = text.slice(..);
         assert_eq!(coords_at_pos(slice, 0), (0, 0).into());
-        assert_eq!(coords_at_pos(slice, 2), (0, 1).into());
-        assert_eq!(coords_at_pos(slice, 3), (0, 2).into());
-        assert_eq!(coords_at_pos(slice, 5), (0, 3).into());
+        assert_eq!(coords_at_pos(slice, 2), (0, 2).into());
+        assert_eq!(coords_at_pos(slice, 3), (0, 3).into());
+        assert_eq!(coords_at_pos(slice, 5), (0, 5).into());
+        assert_eq!(coords_at_pos(slice, 6), (1, 0).into());
     }
 
     #[test]
     fn test_pos_at_coords() {
         let text = Rope::from("ḧëḷḷö\nẅöṛḷḋ");
         let slice = text.slice(..);
-        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
-        assert_eq!(pos_at_coords(slice, (0, 5).into()), 5); // position on \n
-        assert_eq!(pos_at_coords(slice, (1, 0).into()), 6); // position on w
-        assert_eq!(pos_at_coords(slice, (1, 1).into()), 7); // position on o
-        assert_eq!(pos_at_coords(slice, (1, 4).into()), 10); // position on d
+        assert_eq!(pos_at_coords(slice, (0, 0).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 5).into(), false), 5); // position on \n
+        assert_eq!(pos_at_coords(slice, (0, 6).into(), false), 6); // position after \n
+        assert_eq!(pos_at_coords(slice, (0, 6).into(), true), 5); // position after \n
+        assert_eq!(pos_at_coords(slice, (1, 0).into(), false), 6); // position on w
+        assert_eq!(pos_at_coords(slice, (1, 1).into(), false), 7); // position on o
+        assert_eq!(pos_at_coords(slice, (1, 4).into(), false), 10); // position on d
+
+        // Test with wide characters.
+        let text = Rope::from("今日はいい\n");
+        let slice = text.slice(..);
+        assert_eq!(pos_at_coords(slice, (0, 0).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 1).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 2).into(), false), 1);
+        assert_eq!(pos_at_coords(slice, (0, 3).into(), false), 1);
+        assert_eq!(pos_at_coords(slice, (0, 4).into(), false), 2);
+        assert_eq!(pos_at_coords(slice, (0, 6).into(), false), 3);
+        assert_eq!(pos_at_coords(slice, (0, 8).into(), false), 4);
+        assert_eq!(pos_at_coords(slice, (0, 10).into(), false), 5);
+        assert_eq!(pos_at_coords(slice, (0, 11).into(), false), 6);
+        assert_eq!(pos_at_coords(slice, (0, 11).into(), true), 5);
+        assert_eq!(pos_at_coords(slice, (1, 0).into(), false), 6);
 
         // test with grapheme clusters
         let text = Rope::from("a̐éö̲\r\n");
         let slice = text.slice(..);
-        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
-        assert_eq!(pos_at_coords(slice, (0, 1).into()), 2);
-        assert_eq!(pos_at_coords(slice, (0, 2).into()), 4);
-        assert_eq!(pos_at_coords(slice, (0, 3).into()), 7); // \r\n is one char here
-        assert_eq!(pos_at_coords(slice, (0, 4).into()), 9);
+        assert_eq!(pos_at_coords(slice, (0, 0).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 1).into(), false), 2);
+        assert_eq!(pos_at_coords(slice, (0, 2).into(), false), 4);
+        assert_eq!(pos_at_coords(slice, (0, 3).into(), false), 7); // \r\n is one char here
+        assert_eq!(pos_at_coords(slice, (0, 4).into(), false), 9);
+        assert_eq!(pos_at_coords(slice, (0, 4).into(), true), 7);
+        assert_eq!(pos_at_coords(slice, (1, 0).into(), false), 9);
+
         let text = Rope::from("किमपि");
         // 2 - 1 - 2 codepoints
         // TODO: delete handling as per https://news.ycombinator.com/item?id=20058454
         let slice = text.slice(..);
-        assert_eq!(pos_at_coords(slice, (0, 0).into()), 0);
-        assert_eq!(pos_at_coords(slice, (0, 1).into()), 2);
-        assert_eq!(pos_at_coords(slice, (0, 2).into()), 3);
-        assert_eq!(pos_at_coords(slice, (0, 3).into()), 5); // eol
+        assert_eq!(pos_at_coords(slice, (0, 0).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 1).into(), false), 0);
+        assert_eq!(pos_at_coords(slice, (0, 2).into(), false), 2);
+        assert_eq!(pos_at_coords(slice, (0, 3).into(), false), 3);
+        assert_eq!(pos_at_coords(slice, (0, 4).into(), false), 3);
+        assert_eq!(pos_at_coords(slice, (0, 5).into(), false), 5); // eol
     }
 }
diff --git a/helix-core/src/selection.rs b/helix-core/src/selection.rs
index 074b6199..beade27a 100644
--- a/helix-core/src/selection.rs
+++ b/helix-core/src/selection.rs
@@ -286,7 +286,7 @@ impl Selection {
 
         // For 1-width cursor semantics.
         if range.anchor < range.head {
-            prev_grapheme_boundary(text, range.head)
+            prev_grapheme_boundary(text, range.head).max(range.anchor)
         } else {
             range.head
         }
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index 72462741..0ea78f6b 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -917,7 +917,7 @@ fn scroll(cx: &mut Context, offset: usize, direction: Direction) {
         .min(last_line.saturating_sub(scrolloff));
 
     let text = doc.text().slice(..);
-    let pos = pos_at_coords(text, Position::new(line, cursor.col)); // this func will properly truncate to line end
+    let pos = pos_at_coords(text, Position::new(line, cursor.col), true); // this func will properly truncate to line end
 
     // TODO: only manipulate main selection
     doc.set_selection(view.id, Selection::point(pos));
diff --git a/helix-view/src/view.rs b/helix-view/src/view.rs
index 67585ed3..66214691 100644
--- a/helix-view/src/view.rs
+++ b/helix-view/src/view.rs
@@ -97,9 +97,9 @@ impl View {
         const OFFSET: usize = 7; // 1 diagnostic + 5 linenr + 1 gutter
         let last_col = self.first_col + (self.area.width as usize - OFFSET);
 
-        if line > last_line.saturating_sub(scrolloff) {
+        if line > last_line.saturating_sub(scrolloff + 1) {
             // scroll down
-            self.first_line += line - (last_line.saturating_sub(scrolloff));
+            self.first_line += line - (last_line.saturating_sub(scrolloff + 1));
         } else if line < self.first_line + scrolloff {
             // scroll up
             self.first_line = line.saturating_sub(scrolloff);