fix(edit): backspace adds extra spaces for inline virtual text (#28005)

Problem:  Backspace adds extra spaces for inline virtual text.
Solution: Ignore virtual text and wrapping when backspacing.

src/nvim/edit.c

@@ -3673,23 +3673,6 @@ static void ins_del(void)
   AppendCharToRedobuff(K_DEL);
 }
 
-// Delete one character for ins_bs().
-static void ins_bs_one(colnr_T *vcolp)
-{
-  dec_cursor();
-  getvcol(curwin, &curwin->w_cursor, vcolp, NULL, NULL);
-  if (State & REPLACE_FLAG) {
-    // Don't delete characters before the insert point when in
-    // Replace mode
-    if (curwin->w_cursor.lnum != Insstart.lnum
-        || curwin->w_cursor.col >= Insstart.col) {
-      replace_do_bs(-1);
-    }
-  } else {
-    del_char(false);
-  }
-}
-
 /// Handle Backspace, delete-word and delete-line in Insert mode.
 ///
 /// @param          c                 character that was typed
@@ -3846,42 +3829,69 @@ static bool ins_bs(int c, int mode, int *inserted_space_p)
     // Handle deleting one 'shiftwidth' or 'softtabstop'.
     if (mode == BACKSPACE_CHAR
         && ((p_sta && in_indent)
-            || ((get_sts_value() != 0
+            || ((get_sts_value() != 0 || tabstop_count(curbuf->b_p_vsts_array))
-                 || tabstop_count(curbuf->b_p_vsts_array))
                 && curwin->w_cursor.col > 0
                 && (*(get_cursor_pos_ptr() - 1) == TAB
                     || (*(get_cursor_pos_ptr() - 1) == ' '
                         && (!*inserted_space_p || arrow_used)))))) {
-      colnr_T vcol;
-      colnr_T want_vcol;
-
       *inserted_space_p = false;
-      // Compute the virtual column where we want to be.  Since
+
-      // 'showbreak' may get in the way, need to get the last column of
+      bool const use_ts = !curwin->w_p_list || curwin->w_p_lcs_chars.tab1;
-      // the previous character.
+      char *const line = ml_get_buf(curbuf, curwin->w_cursor.lnum);
-      getvcol(curwin, &curwin->w_cursor, &vcol, NULL, NULL);
+      char *const end_ptr = line + curwin->w_cursor.col;
-      colnr_T start_vcol = vcol;
+
-      dec_cursor();
+      colnr_T vcol = 0;
-      getvcol(curwin, &curwin->w_cursor, NULL, NULL, &want_vcol);
+      colnr_T space_vcol = 0;
-      inc_cursor();
+      StrCharInfo sci = utf_ptr2StrCharInfo(line);
-      if (p_sta && in_indent) {
+      StrCharInfo space_sci = sci;
-        int ts = get_sw_value(curbuf);
+      bool prev_space = false;
-        want_vcol = (want_vcol / ts) * ts;
+      while (sci.ptr < end_ptr) {
+        bool cur_space = ascii_iswhite(sci.chr.value);
+        if (!prev_space && cur_space) {
+          space_sci = sci;
+          space_vcol = vcol;
+        }
+        vcol += charsize_nowrap(curbuf, use_ts, vcol, sci.chr.value);
+        sci = utfc_next(sci);
+        prev_space = cur_space;
+      }
+
+      colnr_T want_vcol = vcol - 1;
+      if (want_vcol <= 0) {
+        want_vcol = 0;
+      } else if (p_sta && in_indent) {
+        want_vcol = want_vcol - want_vcol % get_sw_value(curbuf);
       } else {
-        want_vcol = tabstop_start(want_vcol,
+        want_vcol = tabstop_start(want_vcol, get_sts_value(), curbuf->b_p_vsts_array);
-                                  get_sts_value(),
-                                  curbuf->b_p_vsts_array);
       }
 
-      // delete characters until we are at or before want_vcol
+      while (true) {
-      while (vcol > want_vcol && curwin->w_cursor.col > 0
+        int size = charsize_nowrap(curbuf, use_ts, space_vcol, space_sci.chr.value);
-             && (cc = (uint8_t)(*(get_cursor_pos_ptr() - 1)), ascii_iswhite(cc))) {
+        if (space_vcol + size > want_vcol) {
-        ins_bs_one(&vcol);
+          break;
+        }
+        space_vcol += size;
+        space_sci = utfc_next(space_sci);
+      }
+      colnr_T const want_col = (int)(space_sci.ptr - line);
+
+      // Delete characters until we are at or before want_col.
+      while (curwin->w_cursor.col > want_col) {
+        dec_cursor();
+        if (State & REPLACE_FLAG) {
+          // Don't delete characters before the insert point when in Replace mode.
+          if (curwin->w_cursor.lnum != Insstart.lnum
+              || curwin->w_cursor.col >= Insstart.col) {
+            replace_do_bs(-1);
+          }
+        } else {
+          del_char(false);
+        }
       }
 
-      // insert extra spaces until we are at want_vcol
+      // Insert extra spaces until we are at want_vcol.
-      while (vcol < want_vcol) {
+      for (; space_vcol < want_vcol; space_vcol++) {
-        // Remember the first char we inserted
+        // Remember the first char we inserted.
         if (curwin->w_cursor.lnum == Insstart_orig.lnum
             && curwin->w_cursor.col < Insstart_orig.col) {
           Insstart_orig.col = curwin->w_cursor.col;
@@ -3895,13 +3905,6 @@ static bool ins_bs(int c, int mode, int *inserted_space_p)
             replace_push(NUL);
           }
         }
-        getvcol(curwin, &curwin->w_cursor, &vcol, NULL, NULL);
-      }
-
-      // If we are now back where we started delete one character.  Can
-      // happen when using 'sts' and 'linebreak'.
-      if (vcol >= start_vcol) {
-        ins_bs_one(&vcol);
       }
     } else {
       // Delete up to starting point, start of line or previous word.

src/nvim/plines.c

@@ -375,6 +375,18 @@ CharSize charsize_fast(CharsizeArg *csarg, colnr_T const vcol, int32_t const cur
   return charsize_fast_impl(csarg->win, csarg->use_tabstop, vcol, cur_char);
 }
 
+/// Get the number of cells taken up on the screen at given virtual column.
+int charsize_nowrap(buf_T *buf, bool use_tabstop, colnr_T vcol, int32_t cur_char)
+{
+  if (cur_char == TAB && use_tabstop) {
+    return tabstop_padding(vcol, buf->b_p_ts, buf->b_p_vts_array);
+  } else if (cur_char < 0) {
+    return kInvalidByteCells;
+  } else {
+    return char2cells(cur_char);
+  }
+}
+
 /// Check that virtual column "vcol" is in the rightmost column of window "wp".
 ///
 /// @param  wp    window

test/functional/editor/mode_insert_spec.lua

@@ -8,6 +8,7 @@ local command = helpers.command
 local eq = helpers.eq
 local eval = helpers.eval
 local curbuf_contents = helpers.curbuf_contents
+local api = helpers.api
 
 describe('insert-mode', function()
   before_each(function()
@@ -221,4 +222,146 @@ describe('insert-mode', function()
     ]],
     }
   end)
+
+  describe('backspace', function()
+    local function set_lines(line_b, line_e, ...)
+      api.nvim_buf_set_lines(0, line_b, line_e, true, { ... })
+    end
+    local function s(count)
+      return (' '):rep(count)
+    end
+
+    local function test_cols(expected_cols)
+      local cols = { { helpers.fn.col('.'), helpers.fn.virtcol('.') } }
+      for _ = 2, #expected_cols do
+        feed('<BS>')
+        table.insert(cols, { helpers.fn.col('.'), helpers.fn.virtcol('.') })
+      end
+      eq(expected_cols, cols)
+    end
+
+    it('works with tabs and spaces', function()
+      local screen = Screen.new(30, 2)
+      screen:attach()
+      command('setl ts=4 sw=4')
+      set_lines(0, 1, '\t' .. s(4) .. '\t' .. s(9) .. '\t a')
+      feed('$i')
+      test_cols({
+        { 18, 26 },
+        { 17, 25 },
+        { 15, 21 },
+        { 11, 17 },
+        { 7, 13 },
+        { 6, 9 },
+        { 2, 5 },
+        { 1, 1 },
+      })
+    end)
+
+    it('works with varsofttabstop', function()
+      local screen = Screen.new(30, 2)
+      screen:attach()
+      command('setl vsts=6,2,5,3')
+      set_lines(0, 1, 'a\t' .. s(4) .. '\t a')
+      feed('$i')
+      test_cols({
+        { 9, 18 },
+        { 8, 17 },
+        { 8, 14 },
+        { 3, 9 },
+        { 7, 7 },
+        { 2, 2 },
+        { 1, 1 },
+      })
+    end)
+
+    it('works with tab as ^I', function()
+      local screen = Screen.new(30, 2)
+      screen:attach()
+      command('set list listchars=space:.')
+      command('setl ts=4 sw=4')
+      set_lines(0, 1, '\t' .. s(4) .. '\t' .. s(9) .. '\t a')
+      feed('$i')
+      test_cols({
+        { 18, 21 },
+        { 15, 17 },
+        { 11, 13 },
+        { 7, 9 },
+        { 4, 5 },
+        { 1, 1 },
+      })
+    end)
+
+    it('works in replace mode', function()
+      local screen = Screen.new(50, 2)
+      screen:attach()
+      command('setl ts=8 sw=8 sts=8')
+      set_lines(0, 1, '\t' .. s(4) .. '\t' .. s(9) .. '\t a')
+      feed('$R')
+      test_cols({
+        { 18, 34 },
+        { 17, 33 },
+        { 15, 25 },
+        { 7, 17 },
+        { 2, 9 },
+        { 1, 8 }, -- last screen cell of first tab is at vcol 8
+      })
+    end)
+
+    it('works with breakindent', function()
+      local screen = Screen.new(17, 4)
+      screen:attach()
+      command('setl ts=4 sw=4 bri briopt=min:5')
+      set_lines(0, 1, '\t' .. s(4) .. '\t' .. s(9) .. '\t a')
+      feed('$i')
+      test_cols({
+        { 18, 50 },
+        { 17, 49 },
+        { 15, 33 },
+        { 11, 17 },
+        { 7, 13 },
+        { 6, 9 },
+        { 2, 5 },
+        { 1, 1 },
+      })
+    end)
+
+    it('works with inline virtual text', function()
+      local screen = Screen.new(50, 2)
+      screen:attach()
+      command('setl ts=4 sw=4')
+      set_lines(0, 1, '\t' .. s(4) .. '\t' .. s(9) .. '\t a')
+      local ns = api.nvim_create_namespace('')
+      local vt_opts = { virt_text = { { 'text' } }, virt_text_pos = 'inline' }
+      api.nvim_buf_set_extmark(0, ns, 0, 2, vt_opts)
+      feed('$i')
+      test_cols({
+        { 18, 30 },
+        { 17, 29 },
+        { 15, 25 },
+        { 11, 21 },
+        { 7, 17 },
+        { 6, 13 },
+        { 2, 9 },
+        { 1, 5 },
+      })
+    end)
+
+    it("works with 'revins'", function()
+      local screen = Screen.new(30, 3)
+      screen:attach()
+      command('setl ts=4 sw=4 revins')
+      set_lines(0, 1, ('a'):rep(16), s(3) .. '\t' .. s(4) .. '\t a')
+      feed('j$i')
+      test_cols({
+        { 11, 14 },
+        { 10, 13 },
+        { 9, 9 },
+        { 5, 5 },
+        { 1, 1 },
+        { 1, 1 }, -- backspace on empty line does nothing
+      })
+      eq(2, api.nvim_win_get_cursor(0)[1])
+    end)
+  end)
 end)