Check Marked 2 version before running commands

doc/marked.txt

@@ -65,7 +65,9 @@ name or path to the application in your |vimrc|: >
     let g:marked_app = "/Applications/Setapp/Marked 2.app"
 <
 Note that this plugin requires Marked 2. If you are still using Marked 1, you
-can use the 1.0.0 release of this plugin (see |marked-about|).
+can use the 1.0.0 release of this plugin (see |marked-about|). If you still
+have *g:marked_app* set to "Marked", you should update it to "Marked 2" or
+remove it from your |vimrc|.
 
 ==============================================================================
 ABOUT                                           *marked-about*

plugin/marked.vim

@@ -39,13 +39,21 @@ function! s:MarkedOpenURI(background, command, args) abort
 endfunction
 
 function! s:MarkedOpen(background, path) abort
+  if s:MarkedVersionCheck() == 0
+    return
+  endif
+
   call s:AddDocument(a:path)
   call s:MarkedOpenURI(a:background, "open", { "file": a:path })
 
   redraw!
 endfunction
 
 function! s:MarkedQuit(force, path) abort
+  if s:MarkedVersionCheck() == 0
+    return
+  endif
+
   if a:force
     let s:open_documents = []
     call s:RunApplescript("quit")
@@ -58,6 +66,10 @@ function! s:MarkedQuit(force, path) abort
 endfunction
 
 function! s:MarkedPreview(background, line1, line2) abort
+  if s:MarkedVersionCheck() == 0
+    return
+  endif
+
   let lines = getline(a:line1, a:line2)
 
   call s:MarkedOpenURI(a:background, "preview", { "text": join(lines, "\n") })
@@ -73,6 +85,8 @@ let s:js =<< trim JS
       return `error:Couldn't find Marked 2 application.`;
     }
 
+    if (action == "version") return app.version();
+
     if (!app.running()) return;
 
     if (action == "quit") {
@@ -118,6 +132,26 @@ function! s:MarkedQuitVimLeave() abort
   endif
 endfunction
 
+function! s:MarkedVersionCheck() abort
+  if !exists("s:marked_version")
+    let s:marked_version = s:RunApplescript("version")
+  endif
+
+  if s:marked_version =~ "^1"
+    echohl WarningMsg
+    echomsg "marked.vim requires Marked 2 but you've configured it to use Marked 1."
+    echomsg "See `:help g:marked_app` for more information."
+    echohl None
+  elseif s:marked_version !~ "^2"
+    echohl WarningMsg
+    echomsg "This plugin requires Marked 2."
+    echomsg "Visit https://marked2app.com to download it."
+    echohl None
+  end
+
+  return s:marked_version =~ "^2"
+endfunction
+
 function! s:RegisterCommands(filetype) abort
   if index(g:marked_filetypes, a:filetype) >= 0
     command! -buffer -bang          MarkedOpen    call s:MarkedOpen(<bang>0, expand('%:p'))