fix(tui): make setcellwidths() work for non-ambiwidth chars (#28322)

src/nvim/tui/tui.c

@@ -963,17 +963,17 @@ static void print_spaces(TUIData *tui, int width)
   }
 }
 
-/// Move cursor to the position given by `row` and `col` and print the character in `cell`.
-/// This allows the grid and the host terminal to assume different widths of ambiguous-width chars.
+/// Move cursor to the position given by `row` and `col` and print the char in `cell`.
+/// Allows grid and host terminal to assume different widths of ambiguous-width chars.
 ///
-/// @param is_doublewidth  whether the character is double-width on the grid.
-///                        If true and the character is ambiguous-width, clear two cells.
+/// @param is_doublewidth  whether the char is double-width on the grid.
+///                        If true and the char is ambiguous-width, clear two cells.
 static void print_cell_at_pos(TUIData *tui, int row, int col, UCell *cell, bool is_doublewidth)
 {
   UGrid *grid = &tui->grid;
 
   if (grid->row == -1 && cell->data == NUL) {
-    // If cursor needs to repositioned and there is nothing to print, don't move cursor.
+    // If cursor needs repositioning and there is nothing to print, don't move cursor.
     return;
   }
 
@@ -981,10 +981,14 @@ static void print_cell_at_pos(TUIData *tui, int row, int col, UCell *cell, bool
 
   char buf[MAX_SCHAR_SIZE];
   schar_get(buf, cell->data);
-  bool is_ambiwidth = utf_ambiguous_width(utf_ptr2char(buf));
-  if (is_ambiwidth && is_doublewidth) {
+  int c = utf_ptr2char(buf);
+  bool is_ambiwidth = utf_ambiguous_width(c);
+  if (is_doublewidth && (is_ambiwidth || utf_char2cells(c) == 1)) {
+    // If the server used setcellwidths() to treat a single-width char as double-width,
+    // it needs to be treated like an ambiguous-width char.
+    is_ambiwidth = true;
     // Clear the two screen cells.
-    // If the character is single-width in the host terminal it won't change the second cell.
+    // If the char is single-width in host terminal it won't change the second cell.
     update_attrs(tui, cell->attr);
     print_spaces(tui, 2);
     cursor_goto(tui, row, col);
@@ -993,7 +997,7 @@ static void print_cell_at_pos(TUIData *tui, int row, int col, UCell *cell, bool
   print_cell(tui, buf, cell->attr);
 
   if (is_ambiwidth) {
-    // Force repositioning cursor after printing an ambiguous-width character.
+    // Force repositioning cursor after printing an ambiguous-width char.
     grid->row = -1;
   }
 }

test/functional/terminal/tui_spec.lua

@@ -1650,7 +1650,7 @@ describe('TUI', function()
     eq(expected, rv)
   end)
 
-  it('allows grid to assume wider ambiguous-width characters than host terminal #19686', function()
+  it('allows grid to assume wider ambiwidth chars than host terminal', function()
     child_session:request(
       'nvim_buf_set_lines',
       0,
@@ -1694,6 +1694,50 @@ describe('TUI', function()
     screen:expect(singlewidth_screen)
   end)
 
+  it('allows grid to assume wider non-ambiwidth chars than host terminal', function()
+    child_session:request(
+      'nvim_buf_set_lines',
+      0,
+      0,
+      -1,
+      true,
+      { ('✓'):rep(60), ('✓'):rep(60) }
+    )
+    child_session:request('nvim_set_option_value', 'cursorline', true, {})
+    child_session:request('nvim_set_option_value', 'list', true, {})
+    child_session:request('nvim_set_option_value', 'listchars', 'eol:$', { win = 0 })
+    feed_data('gg')
+    local singlewidth_screen = [[
+      {13:✓}{12:✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓}|
+      {12:✓✓✓✓✓✓✓✓✓✓}{15:$}{12:                                       }|
+      ✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓✓|
+      ✓✓✓✓✓✓✓✓✓✓{4:$}                                       |
+      {5:[No Name] [+]                                     }|
+                                                        |
+      {3:-- TERMINAL --}                                    |
+    ]]
+    -- When grid assumes "✓" to be double-width but host terminal assumes it to be single-width,
+    -- the second cell of "✓" is a space and the attributes of the "✓" are applied to it.
+    local doublewidth_screen = [[
+      {13:✓}{12: ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ }|
+      {12:✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ }|
+      {12:✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ }{15:$}{12:                             }|
+      ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ {4:@@@@}|
+      {5:[No Name] [+]                                     }|
+                                                        |
+      {3:-- TERMINAL --}                                    |
+    ]]
+    screen:expect(singlewidth_screen)
+    child_session:request('nvim_set_option_value', 'ambiwidth', 'double', {})
+    screen:expect_unchanged()
+    child_session:request('nvim_call_function', 'setcellwidths', { { { 0x2713, 0x2713, 2 } } })
+    screen:expect(doublewidth_screen)
+    child_session:request('nvim_set_option_value', 'ambiwidth', 'single', {})
+    screen:expect_unchanged()
+    child_session:request('nvim_call_function', 'setcellwidths', { { { 0x2713, 0x2713, 1 } } })
+    screen:expect(singlewidth_screen)
+  end)
+
   it('draws correctly when cursor_address overflows #21643', function()
     t.skip(is_os('mac'), 'FIXME: crashes/errors on macOS')
     screen:try_resize(77, 855)