fix cursors positions when deleting multiple selections (#1393)

* correctly handle overlapping selections merge cursors in Doc:raw_remove

data/core/commands/doc.lua

@@ -323,7 +323,7 @@ local commands = {
   end,
 
   ["doc:delete"] = function(dv)
-    for idx, line1, col1, line2, col2 in dv.doc:get_selections() do
+    for idx, line1, col1, line2, col2 in dv.doc:get_selections(true, true) do
       if line1 == line2 and col1 == col2 and dv.doc.lines[line1]:find("^%s*$", col1) then
         dv.doc:remove(line1, col1, line1, math.huge)
       end
@@ -333,7 +333,7 @@ local commands = {
 
   ["doc:backspace"] = function(dv)
     local _, indent_size = dv.doc:get_indent_info()
-    for idx, line1, col1, line2, col2 in dv.doc:get_selections() do
+    for idx, line1, col1, line2, col2 in dv.doc:get_selections(true, true) do
       if line1 == line2 and col1 == col2 then
         local text = dv.doc:get_text(line1, 1, line1, col1)
         if #text >= indent_size and text:find("^ *$") then

data/core/doc/init.lua

@@ -427,19 +427,51 @@ function Doc:raw_remove(line1, col1, line2, col2, undo_stack, time)
   local before = self.lines[line1]:sub(1, col1 - 1)
   local after = self.lines[line2]:sub(col2)
 
-  -- splice line into line array
-  common.splice(self.lines, line1, line2 - line1 + 1, { before .. after })
+  local line_removal = line2 - line1
+  local col_removal = col2 - col1
 
-  -- move all cursors back if they share a line with the removed text
+  -- splice line into line array
+  common.splice(self.lines, line1, line_removal + 1, { before .. after })
+
+  local merge = false
+
+  -- keep selections in correct positions: each pair (line, col)
+  -- * remains unchanged if before the deleted text
+  -- * is set to (line1, col1) if in the deleted text
+  -- * is set to (line1, col - col_removal) if on line2 but out of the deleted text
+  -- * is set to (line - line_removal, col) if after line2
   for idx, cline1, ccol1, cline2, ccol2 in self:get_selections(true, true) do
-    if cline1 < line2 then break end
-    local line_removal = line2 - line1
-    local column_removal = line2 == cline2 and col2 < ccol1 and (line2 == line1 and col2 - col1 or col2) or 0
-    self:set_selections(idx, cline1 - line_removal, ccol1 - column_removal, cline2 - line_removal, ccol2 - column_removal)
+    if cline2 < line1 then break end
+    local l1, c1, l2, c2 = cline1, ccol1, cline2, ccol2
+
+    if cline1 > line1 or (cline1 == line1 and ccol1 > col1) then
+      if cline1 > line2 then
+        l1 = l1 - line_removal
+      else
+        l1 = line1
+        c1 = (cline1 == line2 and ccol1 > col2) and c1 - col_removal or col1
+      end
+    end
+
+    if cline2 > line1 or (cline2 == line2 and ccol2 > col1) then
+      if cline2 > line2 then
+        l2 = l2 - line_removal
+      else
+        l2 = line1
+        c2 = (cline2 == line2 and ccol2 > col2) and c2 - col_removal or col1
+      end
+    end
+
+    if l1 == line1 and c1 == col1 then merge = true end
+    self:set_selections(idx, l1, c1, l2, c2)
+  end
+
+  if merge then
+    self:merge_cursors()
   end
 
   -- update highlighter and assure selection is in bounds
-  self.highlighter:remove_notify(line1, line2 - line1)
+  self.highlighter:remove_notify(line1, line_removal)
   self:sanitize_selection()
 end