Allow for MarkupContent in completion info (#500)

* allow for MarkdownContent in completion info

* add check for correct type in MarkupContent

* also pass Markdown, and hope for the best

* d'oh!

* advertise plaintext preference in documentation

* fix documentationFormat

Co-Authored-By: Thomas Faingnaert <[email protected]>

Author: Christian Clason

autoload/lsp.vim

@@ -386,6 +386,9 @@ function! lsp#default_get_supported_capabilities(server_info) abort
     \   },
     \   'textDocument': {
     \       'completion': {
+    \           'completionItem': {
+    \              'documentationFormat': ['plaintext']
+    \           },
     \           'completionItemKind': {
     \              'valueSet': lsp#omni#get_completion_item_kinds()
     \           }

autoload/lsp/omni.vim

@@ -268,8 +268,12 @@ function! lsp#omni#default_get_vim_completion_item(item, ...) abort
     endif
 
     if has_key(a:item, 'documentation')
-        if type(a:item['documentation']) == type('')
+        if type(a:item['documentation']) == type('') " field is string
             let l:completion['info'] .= a:item['documentation']
+        elseif type(a:item['documentation']) == type({}) && 
+                    \ has_key(a:item['documentation'], 'value')
+            " field is MarkupContent (hopefully 'plaintext')
+            let l:completion['info'] .= a:item['documentation']['value']
         endif
     endif