lsp: add incremental text synchronization

* Implementation derived from and validated by vim-lsc authored by Nate
  Bosch

runtime/lua/vim/lsp.lua

@@ -262,6 +262,13 @@ end
 --@param bufnr (Number) Number of the buffer, or 0 for current
 --@param client Client object
 local function text_document_did_open_handler(bufnr, client)
+  local allow_incremental_sync = if_nil(client.config.flags.allow_incremental_sync, false)
+  if allow_incremental_sync then
+    if not client._cached_buffers then
+      client._cached_buffers = {}
+    end
+    client._cached_buffers[bufnr] = nvim_buf_get_lines(bufnr, 0, -1, true)
+  end
   if not client.resolved_capabilities.text_document_open_close then
     return
   end
@@ -808,7 +815,6 @@ end
 --- Notify all attached clients that a buffer has changed.
 local text_document_did_change_handler
 do
-  local encoding_index = { ["utf-8"] = 1; ["utf-16"] = 2; ["utf-32"] = 3; }
   text_document_did_change_handler = function(_, bufnr, changedtick,
       firstline, lastline, new_lastline, old_byte_size, old_utf32_size,
       old_utf16_size)
@@ -827,23 +833,12 @@ do
     util.buf_versions[bufnr] = changedtick
     -- Lazy initialize these because clients may not even need them.
     local incremental_changes = once(function(client)
-      local size_index = encoding_index[client.offset_encoding]
-      local length = select(size_index, old_byte_size, old_utf16_size, old_utf32_size)
-      local lines = nvim_buf_get_lines(bufnr, firstline, new_lastline, true)
-
-      -- This is necessary because we are specifying the full line including the
-      -- newline in range. Therefore, we must replace the newline as well.
-      if #lines > 0 then
-       table.insert(lines, '')
-      end
-      return {
-        range = {
-          start = { line = firstline, character = 0 };
-          ["end"] = { line = lastline, character = 0 };
-        };
-        rangeLength = length;
-        text = table.concat(lines, '\n');
-      };
+      local lines = nvim_buf_get_lines(bufnr, 0, -1, true)
+      local startline =  math.min(firstline + 1, math.min(#client._cached_buffers[bufnr], #lines))
+      local endline =  math.min(-(#lines - new_lastline), 0)
+      local incremental_change = vim.lsp.util.compute_diff(client._cached_buffers[bufnr], lines, startline, endline)
+      client._cached_buffers[bufnr] = lines
+      return incremental_change
     end)
     local full_changes = once(function()
       return {
@@ -931,6 +926,9 @@ function lsp.buf_attach_client(bufnr, client_id)
           if client.resolved_capabilities.text_document_open_close then
             client.notify('textDocument/didClose', params)
           end
+          if client._cached_buffers then
+            client._cached_buffers[bufnr] = nil
+          end
         end)
         util.buf_versions[bufnr] = nil
         all_buffer_active_clients[bufnr] = nil

runtime/lua/vim/lsp/util.lua

@@ -226,6 +226,165 @@ end
 -- function M.glob_to_regex(glob)
 -- end
 
+--@private
+--- Finds the first line and column of the difference between old and new lines
+--@param old_lines table list of lines
+--@param new_lines table list of lines
+--@returns (int, int) start_line_idx and start_col_idx of range
+local function first_difference(old_lines, new_lines, start_line_idx)
+  local line_count = math.min(#old_lines, #new_lines)
+  if line_count == 0 then return 1, 1 end
+  if not start_line_idx then
+    for i = 1, line_count do
+      start_line_idx = i
+      if old_lines[start_line_idx] ~= new_lines[start_line_idx] then
+        break
+      end
+    end
+  end
+  local old_line = old_lines[start_line_idx]
+  local new_line = new_lines[start_line_idx]
+  local length = math.min(#old_line, #new_line)
+  local start_col_idx = 1
+  while start_col_idx <= length do
+    if string.sub(old_line, start_col_idx, start_col_idx) ~= string.sub(new_line, start_col_idx, start_col_idx) then
+      break
+    end
+    start_col_idx  = start_col_idx  + 1
+  end
+  return start_line_idx, start_col_idx
+end
+
+
+--@private
+--- Finds the last line and column of the differences between old and new lines
+--@param old_lines table list of lines
+--@param new_lines table list of lines
+--@param start_char integer First different character idx of range
+--@returns (int, int) end_line_idx and end_col_idx of range
+local function last_difference(old_lines, new_lines, start_char, end_line_idx)
+  local line_count = math.min(#old_lines, #new_lines)
+  if line_count == 0 then return 0,0 end
+  if not end_line_idx then
+    end_line_idx = -1
+  end
+  for i = end_line_idx, -line_count, -1  do
+    if old_lines[#old_lines + i + 1] ~= new_lines[#new_lines + i + 1] then
+      end_line_idx = i
+      break
+    end
+  end
+  local old_line
+  local new_line
+  if end_line_idx <= -line_count then
+    end_line_idx = -line_count
+    old_line  = string.sub(old_lines[#old_lines + end_line_idx + 1], start_char)
+    new_line  = string.sub(new_lines[#new_lines + end_line_idx + 1], start_char)
+  else
+    old_line  = old_lines[#old_lines + end_line_idx + 1]
+    new_line  = new_lines[#new_lines + end_line_idx + 1]
+  end
+  local old_line_length = #old_line
+  local new_line_length = #new_line
+  local length = math.min(old_line_length, new_line_length)
+  local end_col_idx = -1
+  while end_col_idx >= -length do
+    local old_char =  string.sub(old_line, old_line_length + end_col_idx + 1, old_line_length + end_col_idx + 1)
+    local new_char =  string.sub(new_line, new_line_length + end_col_idx + 1, new_line_length + end_col_idx + 1)
+    if old_char ~= new_char then
+      break
+    end
+    end_col_idx = end_col_idx - 1
+  end
+  return end_line_idx, end_col_idx
+
+end
+
+--@private
+--- Get the text of the range defined by start and end line/column
+--@param lines table list of lines
+--@param start_char integer First different character idx of range
+--@param end_char integer Last different character idx of range
+--@param start_line integer First different line idx of range
+--@param end_line integer Last different line idx of range
+--@returns string text extracted from defined region
+local function extract_text(lines, start_line, start_char, end_line, end_char)
+  if start_line == #lines + end_line + 1 then
+    if end_line == 0 then return '' end
+    local line = lines[start_line]
+    local length = #line + end_char - start_char
+    return string.sub(line, start_char, start_char + length + 1)
+  end
+  local result = string.sub(lines[start_line], start_char) .. '\n'
+  for line_idx = start_line + 1, #lines + end_line do
+    result = result .. lines[line_idx] .. '\n'
+  end
+  if end_line ~= 0 then
+    local line = lines[#lines + end_line + 1]
+    local length = #line + end_char + 1
+    result = result .. string.sub(line, 1, length)
+  end
+  return result
+end
+
+--@private
+--- Compute the length of the substituted range
+--@param lines table list of lines
+--@param start_char integer First different character idx of range
+--@param end_char integer Last different character idx of range
+--@param start_line integer First different line idx of range
+--@param end_line integer Last different line idx of range
+--@returns (int, int) end_line_idx and end_col_idx of range
+local function compute_length(lines, start_line, start_char, end_line, end_char)
+  local adj_end_line = #lines + end_line + 1
+  local adj_end_char
+  if adj_end_line > #lines then
+    adj_end_char =  end_char - 1
+  else
+    adj_end_char = #lines[adj_end_line] + end_char
+  end
+  if start_line == adj_end_line then
+    return adj_end_char - start_char + 1
+  end
+  local result = #lines[start_line] - start_char + 1
+  for line = start_line + 1, adj_end_line -1 do
+    result = result + #lines[line] + 1
+  end
+  result = result + adj_end_char + 1
+  return result
+end
+
+--- Returns the range table for the difference between old and new lines
+--@param old_lines table list of lines
+--@param new_lines table list of lines
+--@returns table start_line_idx and start_col_idx of range
+function M.compute_diff(old_lines, new_lines, start_line_idx, end_line_idx)
+  local start_line, start_char = first_difference(old_lines, new_lines, start_line_idx)
+  local end_line, end_char = last_difference(vim.list_slice(old_lines, start_line, #old_lines),
+      vim.list_slice(new_lines, start_line, #new_lines), start_char, end_line_idx)
+  local text = extract_text(new_lines, start_line, start_char, end_line, end_char)
+  local length = compute_length(old_lines, start_line, start_char, end_line, end_char)
+
+  local adj_end_line = #old_lines + end_line
+  local adj_end_char
+  if end_line == 0 then
+    adj_end_char = 0
+  else
+    adj_end_char = #old_lines[#old_lines + end_line + 1] + end_char + 1
+  end
+
+  local result = {
+    range = {
+      start = { line = start_line - 1, character = start_char - 1},
+      ["end"] = { line = adj_end_line, character = adj_end_char}
+    },
+    text = text,
+    rangeLength = length + 1,
+  }
+
+  return result
+end
+
 --- Can be used to extract the completion items from a
 --- `textDocument/completion` request, which may return one of
 --- `CompletionItem[]`, `CompletionList` or null.

runtime/lua/vim/shared.lua

@@ -400,6 +400,20 @@ function vim.tbl_count(t)
   return count
 end
 
+--- Creates a copy of a table containing only elements from start to end (inclusive)
+---
+--@param list table table
+--@param start integer Start range of slice
+--@param finish integer End range of slice
+--@returns Copy of table sliced from start to finish (inclusive)
+function vim.list_slice(list, start, finish)
+  local new_list = {}
+  for i = start or 1, finish or #list do
+    new_list[#new_list+1] = list[i]
+  end
+  return new_list
+end
+
 --- Trim whitespace (Lua pattern "%s") from both sides of a string.
 ---
 --@see https://www.lua.org/pil/20.2.html