3 files changed, 23 insertions, 10 deletions
diff --git a/runtime/lua/vim/lsp/handlers.lua b/runtime/lua/vim/lsp/handlers.lua
index 0cf80e1443..eacbd90077 100644
--- a/runtime/lua/vim/lsp/handlers.lua
+++ b/runtime/lua/vim/lsp/handlers.lua
@@ -304,7 +304,7 @@ M['textDocument/typeDefinition'] = location_handler
 M['textDocument/implementation'] = location_handler
 
 --@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_signatureHelp
-M['textDocument/signatureHelp'] = function(_, method, result)
+M['textDocument/signatureHelp'] = function(_, method, result, _, bufnr)
   -- When use `autocmd CompleteDone <silent><buffer> lua vim.lsp.buf.signature_help()` to call signatureHelp handler
   -- If the completion item doesn't have signatures It will make noise. Change to use `print` that can use `<silent>` to ignore
   if not (result and result.signatures and result.signatures[1]) then
@@ -317,9 +317,11 @@ M['textDocument/signatureHelp'] = function(_, method, result)
     print('No signature help available')
     return
   end
-  util.focusable_preview(method, function()
+  local syntax = api.nvim_buf_get_option(bufnr, 'syntax')
+  local p_bufnr, _ = util.focusable_preview(method, function()
     return lines, util.try_trim_markdown_code_blocks(lines)
   end)
+  api.nvim_buf_set_option(p_bufnr, 'syntax', syntax)
 end
 
 --@see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_documentHighlight
diff --git a/runtime/lua/vim/lsp/rpc.lua b/runtime/lua/vim/lsp/rpc.lua
index 4e2dd7c8e8..1aa8326514 100644
--- a/runtime/lua/vim/lsp/rpc.lua
+++ b/runtime/lua/vim/lsp/rpc.lua
@@ -315,8 +315,10 @@ local function start(cmd, cmd_args, dispatchers, extra_spawn_params)
     dispatchers = { dispatchers, 't', true };
   }
 
-  if not (vim.fn.executable(cmd) == 1) then
-    error(string.format("The given command %q is not executable.", cmd))
+  if extra_spawn_params and extra_spawn_params.cwd then
+      assert(is_dir(extra_spawn_params.cwd), "cwd must be a directory")
+  elseif not (vim.fn.executable(cmd) == 1) then
+      error(string.format("The given command %q is not executable.", cmd))
   end
   if dispatchers then
     local user_dispatchers = dispatchers
@@ -370,9 +372,6 @@ local function start(cmd, cmd_args, dispatchers, extra_spawn_params)
     }
     if extra_spawn_params then
       spawn_params.cwd = extra_spawn_params.cwd
-      if spawn_params.cwd then
-        assert(is_dir(spawn_params.cwd), "cwd must be a directory")
-      end
       spawn_params.env = env_merge(extra_spawn_params.env)
     end
     handle, pid = uv.spawn(cmd, spawn_params, onexit)
diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index a75ab37508..ec1131ae1f 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -357,8 +357,11 @@ 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
+--@param start_line_idx int line to begin search for first difference
+--@param end_line_idx int line to begin search for last difference
+--@param offset_encoding string encoding requested by language server
 --@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)
+function M.compute_diff(old_lines, new_lines, start_line_idx, end_line_idx, offset_encoding)
   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)
@@ -373,10 +376,19 @@ function M.compute_diff(old_lines, new_lines, start_line_idx, end_line_idx)
     adj_end_char = #old_lines[#old_lines + end_line + 1] + end_char + 1
   end
 
+  local _
+  if offset_encoding == "utf-16" then
+    _, start_char = vim.str_utfindex(old_lines[start_line], start_char - 1)
+    _, end_char = vim.str_utfindex(old_lines[#old_lines + end_line + 1], adj_end_char)
+  else
+    start_char = start_char - 1
+    end_char = adj_end_char
+  end
+
   local result = {
     range = {
-      start = { line = start_line - 1, character = start_char - 1},
-      ["end"] = { line = adj_end_line, character = adj_end_char}
+      start = { line = start_line - 1, character = start_char},
+      ["end"] = { line = adj_end_line, character = end_char}
     },
     text = text,
     rangeLength = length + 1,