Handle scrolling when hover popup is open

There are two kinds of scrolling that need to be handled:
1. Scrolling the buffer in a window shifts the buffer, but popups stay
   in place. Instead, we close the popup whenever we receive a
   WinScrolled event.
2. Scrolling the popup contents themselves resets the `updatetime` timer
   and can trigger a second CursorHold event, which leads to YCM
   resetting the hover popup. Instead, only re-display the hover popup
   if it is not already visible.

autoload/youcompleteme.vim

@@ -717,6 +717,7 @@ function! s:EnableAutoHover()
     augroup YcmBufHover
       autocmd! * <buffer>
       autocmd CursorHold <buffer> call s:Hover()
+      autocmd WinScrolled <buffer> call popup_close( s:cursorhold_popup )
     augroup END
   endif
 endfunction
@@ -1621,9 +1622,11 @@ if exists( '*popup_atcursor' )
       return
     endif
 
-    call youcompleteme#GetCommandResponseAsync(
-          \ function( 's:ShowHoverResult' ),
-          \ b:ycm_hover.command )
+    if empty( popup_getpos( s:cursorhold_popup ) )
+      call youcompleteme#GetCommandResponseAsync(
+            \ function( 's:ShowHoverResult' ),
+            \ b:ycm_hover.command )
+    endif
   endfunction
 
 

test/hover.test.vim

@@ -482,3 +482,27 @@ function! Test_Long_Wrapped()
 
   call popup_clear()
 endfunction
+
+function! Test_Long_Scrolling()
+  let f = tempname() . '.cc'
+  execut 'edit' f
+  let lines = repeat( [ ' * aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' ], 50 )
+  call insert( lines, 0, '/**' )
+  call extend( lines, [ ' */', 'void f();' ] )
+  call setline( 1, lines )
+  call cursor( [ 54, 6 ] )
+  normal \D
+  call WaitForAssert( { -> assert_equal( 1, popup_list() ) } )
+  let popup_id = popup_list()[ 0 ]
+  call test_setmouse( 15, 15 )
+  call feedkeys( "\<ScrollWheelDown>", "xt" )
+  let win_info = getwininfo( popup_id )[ 0 ]
+  call assert_notequal( 1, win_info[ 'topline' ] )
+  doautocmd CursorHold
+  sleep 1
+  let win_info = getwininfo( popup_id )[ 0 ]
+  call assert_notequal( 1, win_info[ 'topline' ] )
+  call test_setmouse( 15 + win_info[ 'height' ], 15 )
+  call feedkeys( "\<ScrollWheelDown>", "xt" )
+  call assert_equal( 0, popup_list() )
+endfunction