improve diff by using lua if available (#821)

* use lua if available for diff

* add docs

* sync with latest vim-lsc changes

* lazily init lua

* update vim to 8.2.0817

* update vim to 8.2.0817 for windows

* use vim 8.2.0814

* check for path 8.2.0775 before enabling lua

* use vim 8.2.0813 since it exists for both linux and windows

* update lua patch check

* optimize vimscript diff by using range

* fix lint issues

.github/workflows/linux_vim.yml

@@ -18,7 +18,7 @@ jobs:
         include:
           - name: vim-v82-x64
             os: ubuntu-latest
-            vim_version: 8.2.0037
+            vim_version: 8.2.0813
             glibc_version: 2.15
           - name: vim-v81-x64
             os: ubuntu-latest

.github/workflows/windows_vim.yml

@@ -18,7 +18,7 @@ jobs:
         include:
           - name: vim-v82-x64
             os: windows-latest
-            vim_version: 8.2.0037
+            vim_version: 8.2.0813
             vim_arch: x64
             vim_ver_path: vim82
           - name: vim-v81-x64

README.md

@@ -11,6 +11,11 @@ Plug 'prabirshrestha/vim-lsp'
 
 _Note: [async.vim](https://github.com/prabirshrestha/async.vim) is required and is used to normalize jobs between vim8 and neovim._
 
+__Performance__
+
+Certain bottlenecks in VimScript have been implemented in lua. If you would like to take advantage of these performance gains
+use vim compiled with lua or neovim v0.4.0+
+
 ## Registering servers
 
 ```viml

autoload/lsp/utils/diff.vim

@@ -6,6 +6,40 @@
 " definition of `TextDocumentContentChangeEvent`.
 "
 " Finds a single change between the common prefix, and common postfix.
+let s:has_lua = has('nvim-0.4.0') || (has('lua') && has('patch-8.2.0775'))
+
+function! s:init_lua() abort
+  lua <<EOF
+  -- Returns a zero-based index of the last line that is different between
+  -- old and new. If old and new are not zero indexed, pass offset to indicate
+  -- the index base.
+  function vimlsp_last_difference(old, new, offset, line_count)
+    for i = 0, line_count - 1 do
+      if old[#old - i + offset] ~= new[#new - i + offset] then
+        return -1 * i
+      end
+    end
+    return -1 * line_count
+  end
+  -- Returns a zero-based index of the first line that is different between
+  -- old and new. If old and new are not zero indexed, pass offset to indicate
+  -- the index base.
+  function vimlsp_first_difference(old, new, offset, line_count)
+    for i = 0, line_count - 1 do
+      if old[i + offset] ~= new[i + offset] then
+        return i
+      end
+    end
+    return line_count - 1
+  end
+EOF
+	let s:lua = 1
+endfunction
+
+if s:has_lua && !exists('s:lua')
+  call s:init_lua()
+endif
+
 function! lsp#utils#diff#compute(old, new) abort
   let [l:start_line, l:start_char] = s:FirstDifference(a:old, a:new)
   let [l:end_line, l:end_char] =
@@ -31,11 +65,15 @@ endfunction
 function! s:FirstDifference(old, new) abort
   let l:line_count = min([len(a:old), len(a:new)])
   if l:line_count == 0 | return [0, 0] | endif
-  let l:i = 0
-  while l:i < l:line_count
-    if a:old[l:i] !=# a:new[l:i] | break | endif
-    let l:i += 1
-  endwhile
+  if g:lsp_use_lua && s:has_lua
+    let l:eval = has('nvim') ? 'vim.api.nvim_eval' : 'vim.eval'
+    let l:i = luaeval('vimlsp_first_difference('
+        \.l:eval.'("a:old"),'.l:eval.'("a:new"),'.l:eval.'("has(\"nvim\")"),'.l:line_count.')')
+  else
+	for l:i in range(l:line_count)
+	  if a:old[l:i] !=# a:new[l:i] | break | endif
+	endfor
+  endif
   if l:i >= l:line_count
     return [l:line_count - 1, strchars(a:old[l:line_count - 1])]
   endif
@@ -53,11 +91,15 @@ endfunction
 function! s:LastDifference(old, new, start_char) abort
   let l:line_count = min([len(a:old), len(a:new)])
   if l:line_count == 0 | return [0, 0] | endif
-  let l:i = -1
-  while l:i >= -1 * l:line_count
-    if a:old[l:i] !=# a:new[l:i] | break | endif
-    let l:i -= 1
-  endwhile
+  if g:lsp_use_lua && s:has_lua
+    let l:eval = has('nvim') ? 'vim.api.nvim_eval' : 'vim.eval'
+    let l:i = luaeval('vimlsp_last_difference('
+        \.l:eval.'("a:old"),'.l:eval.'("a:new"),'.l:eval.'("has(\"nvim\")"),'.l:line_count.')')
+  else
+	for l:i in range(-1, -1 * l:line_count, -1)
+	  if a:old[l:i] !=# a:new[l:i] | break | endif
+	endfor
+  endif
   if l:i <= -1 * l:line_count
     let l:i = -1 * l:line_count
     let l:old_line = strcharpart(a:old[l:i], a:start_char)

doc/vim-lsp.txt

@@ -6,6 +6,7 @@ CONTENTS                                                  *vim-lsp-contents*
 
     Introduction                          |vim-lsp-introduction|
     Install                               |vim-lsp-install|
+    Performance                           |vim-lsp-performance|
     Language Servers                      |vim-lsp-language-servers|
       Configure                             |vim-lsp-configure|
       vim-lsp-settings                      |vim-lsp-settings_plugin|
@@ -132,6 +133,25 @@ Install the async.vim and vim-lsp plugins. Below is a sample using plug.vim
 Note:  async.vim (https://github.com/prabirshrestha/async.vim) is required to
 use vim-lsp. It is used to normalize the jobs api between Vim 8 and Neovim.
 
+==============================================================================
+PERFORMANCE                                          *vim-lsp-performance*
+
+While VimScript is very portable it has performance implications. If you would
+like to improve performance make sure you have vim/neovim with lua support.
+Currently only diff algorithm uses lua internally if available.
+Following is th default value used to detect lua.
+>
+    let g:lsp_enable_lua = has('nvim-0.4.0') || (has('lua') && has('patch-8.2.0775'))
+
+Windows users can download the binaries from the following url and place
+lua53.dll in the `PATH` or besides `vim.exe` or `gvim.exe` executables.
+
+32 bit:
+http://downloads.sourceforge.net/luabinaries/lua-5.3.2_Win32_dllw4_lib.zip
+
+64bit:
+http://downloads.sourceforge.net/luabinaries/lua-5.3.2_Win64_dllw4_lib.zip
+
 ==============================================================================
 LANGUAGE SERVERS                                 *vim-lsp-language-servers*
 

plugin/lsp.vim

@@ -3,6 +3,7 @@ if exists('g:lsp_loaded') || !exists('*json_encode') || !has('timers') || !has('
 endif
 let g:lsp_loaded = 1
 
+let g:lsp_use_lua = get(g:, 'lsp_use_lua', has('nvim-0.4.0') || (has('lua') && has('patch-8.2.0775')))
 let g:lsp_auto_enable = get(g:, 'lsp_auto_enable', 1)
 let g:lsp_async_completion = get(g:, 'lsp_async_completion', 0)
 let g:lsp_log_file = get(g:, 'lsp_log_file', '')