Allow setting popup max width

autoload/lsp/ui/vim/output.vim

@@ -113,10 +113,16 @@ function! lsp#ui#vim#output#floatingpreview(data) abort
     " Enable closing the preview with esc, but map only in the scratch buffer
     nmap <buffer><silent> <esc> :pclose<cr>
   else
-    let s:winid = popup_atcursor('...', {
-        \  'moved': 'any',
-		    \  'border': [1, 1, 1, 1],
-		\})
+    let l:options = {
+                \ 'moved': 'any',
+                \ 'border': [1, 1, 1, 1],
+                \ }
+
+    if g:lsp_preview_max_width > 0
+        let l:options['maxwidth'] = g:lsp_preview_max_width
+    endif
+
+    let s:winid = popup_atcursor('...', l:options)
   endif
   return s:winid
 endfunction
@@ -139,6 +145,13 @@ function! s:setcontent(lines, ft) abort
   else
     " nvim floating
     call setline(1, a:lines)
+
+    " Set maximum width of floating window, if specified
+    if g:lsp_preview_max_width > 0
+        let &l:textwidth = g:lsp_preview_max_width
+        normal! gggqGgg
+    endif
+
     setlocal readonly nomodifiable
     let &l:filetype = a:ft . '.lsp-hover'
   endif

doc/vim-lsp.txt

@@ -27,6 +27,7 @@ CONTENTS                                                  *vim-lsp-contents*
       g:lsp_highlight_references_enabled    |g:lsp_highlight_references_enabled|
       g:lsp_get_vim_completion_item         |g:lsp_get_vim_completion_item|
       g:lsp_get_supported_capabilities      |g:lsp_get_supported_capabilities|
+      g:lsp_preview_max_width               |g:lsp_preview_max_width|
     Functions                             |vim-lsp-functions|
       enable                                |vim-lsp-enable|
       disable                               |vim-lsp-disable|
@@ -382,6 +383,15 @@ g:lsp_get_supported_capabilities         *g:lsp_get_supported_capabilities*
     calling `lsp#omni#default_get_supported_capabilities` from within your
     function.
 
+g:lsp_preview_max_width                           *g:lsp_preview_max_width*
+    Type: |Number|
+    Default: `-1`
+
+    If positive, determines the maximum width of the preview window in
+    characters. Lines longer than `g:lsp_preview_max_width` will be wrapped to
+    fit in the preview window. Use a value of `-1` to disable setting a
+    maximum width.
+
 ===============================================================================
 FUNCTIONS	                                        *vim-lsp-functions*
 
@@ -750,7 +760,7 @@ Closes an opened preview window
 Transfers focus to an opened preview window or back to the previous window if
 focus is already on the preview window.
 
-  
+
 ===============================================================================
 Autocomplete                                          *vim-lsp-autocomplete*
 

plugin/lsp.vim

@@ -28,6 +28,7 @@ let g:lsp_highlight_references_enabled = get(g:, 'lsp_highlight_references_enabl
 let g:lsp_preview_float = get(g:, 'lsp_preview_float', 1)
 let g:lsp_preview_autoclose = get(g:, 'lsp_preview_autoclose', 1)
 let g:lsp_preview_doubletap = get(g:, 'lsp_preview_doubletap', [function('lsp#ui#vim#output#focuspreview')])
+let g:lsp_preview_max_width = get(g:, 'lsp_preview_max_width', -1)
 
 let g:lsp_get_vim_completion_item = get(g:, 'lsp_get_vim_completion_item', [function('lsp#omni#default_get_vim_completion_item')])
 let g:lsp_get_supported_capabilities = get(g:, 'lsp_get_supported_capabilities', [function('lsp#default_get_supported_capabilities')])