add g:lsp_hover_ui

autoload/lsp/internal/document_hover/under_cursor.vim

@@ -12,7 +12,7 @@ let s:Buffer = vital#lsp#import('VS.Vim.Buffer')
 " }
 function! lsp#internal#document_hover#under_cursor#do(options) abort
     let l:bufnr = bufnr('%')
-    let l:ui = get(a:options, 'ui', g:lsp_preview_float ? 'float' : 'preview')
+    let l:ui = get(a:options, 'ui', s:FloatingWindow.is_available() ? 'float' : 'preview')
     if has_key(a:options, 'server')
         let l:servers = [a:options['server']]
     else
@@ -63,11 +63,9 @@ function! s:show_hover(ui, server_name, request, response) abort
     if s:FloatingWindow.is_available() && a:ui ==? 'float'
 		" show floating window
 		call s:show_floating_window(a:server_name, a:request, a:response)
-    elseif a:ui ==? 'preview'
+    else
         " FIXME: user preview window
         call lsp#ui#vim#output#preview(a:server_name, a:response['result']['contents'], {'statusline': ' LSP Hover'})
-    else
-        call lsp#utils#error('Invalid ui for LspHover')
 	endif
 endfunction
 

doc/vim-lsp.txt

@@ -65,6 +65,7 @@ CONTENTS                                                  *vim-lsp-contents*
       g:lsp_signature_help_enabled          |g:lsp_signature_help_enabled|
       g:lsp_fold_enabled                    |g:lsp_fold_enabled|
       g:lsp_hover_conceal                   |g:lsp_hover_conceal|
+      g:lsp_hover_ui			    |g:lsp_hover_ui|
       g:lsp_ignorecase                      |g:lsp_ignorecase|
       g:lsp_log_file                        |g:lsp_log_file|
       g:lsp_semantic_enabled                |g:lsp_semantic_enabled|
@@ -859,6 +860,19 @@ g:lsp_hover_conceal                                   *g:lsp_hover_conceal*
     To override this setting per server, see
     |vim-lsp-server_info-hover_conceal|.
 
+g:lsp_hover_ui                                                *g:lsp_hover_ui*
+    Type: |String|
+    Default: `''`
+
+    Controls deafult UI behavior for |LspHover|.
+    If empty string, defaults to `float` is popup is supported in vim or
+    floating window is supported in neovim else uses |preview-window|.
+
+    Example: >
+	let g:lsp_hover_ui = ''
+	let g:lsp_hover_ui = 'float'
+	let g:lsp_hover_ui = 'preview'
+
 g:lsp_ignorecase                                         *g:lsp_ignorecase*
     Type: |Boolean|
     Default: the value of 'ignorecase'

plugin/lsp.vim

@@ -60,6 +60,7 @@ let g:lsp_signature_help_delay = get(g:, 'lsp_signature_help_delay', 200)
 let g:lsp_show_workspace_edits = get(g:, 'lsp_show_workspace_edits', 0)
 let g:lsp_fold_enabled = get(g:, 'lsp_fold_enabled', 1)
 let g:lsp_hover_conceal = get(g:, 'lsp_hover_conceal', 1)
+let g:lsp_hover_ui = get(g:, 'lsp_hover_ui', '')
 let g:lsp_ignorecase = get(g:, 'lsp_ignorecase', &ignorecase)
 let g:lsp_semantic_enabled = get(g:, 'lsp_semantic_enabled', 0)
 let g:lsp_text_document_did_save_delay = get(g:, 'lsp_text_document_did_save_delay', -1)