Use popup window for hover preview

autoload/lsp/ui/vim/output.vim

@@ -1,49 +1,52 @@
 function! lsp#ui#vim#output#preview(data) abort
-    " Close any previously opened preview window
-    pclose
+    if has('patch-8.1.1517')
+        let l:winid = popup_atcursor('...', {
+        \  'moved': 'any',
+		\  'border': [1, 1, 1, 1],
+		\})
+        let l:buf = winbufnr(l:winid)
+        let [l:ft, l:lines] = s:tolines(a:data)
+        call setbufline(l:buf, 1, split(l:lines, "\n"))
+        call win_execute(l:winid, 'setlocal filetype=' . l:ft . '.lsp-hover')
+    else
+        " Close any previously opened preview window
+        pclose
 
-    let l:current_window_id = win_getid()
+        let l:current_window_id = win_getid()
 
-    execute &previewheight.'new'
+        execute &previewheight.'new'
 
-    let l:ft = s:append(a:data)
-    " Delete first empty line
-    0delete _
+        let [l:ft, l:lines] = s:tolines(a:data)
+        call setline(1, split(l:lines, "\n"))
 
-    setlocal readonly nomodifiable
+        setlocal readonly nomodifiable
 
-    let &l:filetype = l:ft . '.lsp-hover'
+        let &l:filetype = l:ft . '.lsp-hover'
 
-    if g:lsp_preview_keep_focus
-      " restore focus to the previous window
-      call win_gotoid(l:current_window_id)
-    endif
+        if g:lsp_preview_keep_focus
+          " restore focus to the previous window
+          call win_gotoid(l:current_window_id)
+        endif
 
-    echo ''
+        echo ''
+    endif
 
     return ''
 endfunction
 
-function! s:append(data) abort
+function! s:tolines(data) abort
     if type(a:data) == type([])
+        let l:lines = ''
         for l:entry in a:data
-            call s:append(entry)
+            let l:lines .= s:tolines(l:entry)[1] . "\n"
         endfor
-
-        return 'markdown'
+        return ['markdown', l:lines]
     elseif type(a:data) == type('')
-        silent put =a:data
-
-        return 'markdown'
+        return ['markdown', a:data]
     elseif type(a:data) == type({}) && has_key(a:data, 'language')
-        silent put ='```'.a:data.language
-        silent put =a:data.value
-        silent put ='```'
-
-        return 'markdown'
+        return ['markdown', '```' . a:data.language . "\n" . a:data.value . "\n```\n"]
     elseif type(a:data) == type({}) && has_key(a:data, 'kind')
-        silent put =a:data.value
-
-        return a:data.kind ==? 'plaintext' ? 'text' : a:data.kind
+        return [a:data.kind ==? 'plaintext' ? 'text' : a:data.kind, a:data.value]
     endif
+    return ['', '']
 endfunction