add keyboard scrolling and dismiss to floating preview popups

vim floating preview windows had no keyboard scrolling support so
long hover or detail content was inaccessible without a mouse,
adds a popup filter with ctrl-n/ctrl-p for line scroll, ctrl-d/ctrl-u
for page scroll, and escape to dismiss

Author: coriocactus

autoload/ale/floating_preview.vim

@@ -144,6 +144,32 @@ function! s:NvimCreate(options) abort
     let w:preview = {'id': l:winid, 'buffer': l:buffer}
 endfunction
 
+function! ale#floating_preview#PopupFilter(winid, key) abort
+    if a:key is# "\<C-n>" || a:key is# "\<ScrollWheelDown>"
+        call win_execute(a:winid, "normal! \<C-e>")
+
+        return 1
+    elseif a:key is# "\<C-p>" || a:key is# "\<ScrollWheelUp>"
+        call win_execute(a:winid, "normal! \<C-y>")
+
+        return 1
+    elseif a:key is# "\<C-d>"
+        call win_execute(a:winid, "normal! \<C-d>")
+
+        return 1
+    elseif a:key is# "\<C-u>"
+        call win_execute(a:winid, "normal! \<C-u>")
+
+        return 1
+    elseif a:key is# "\<Esc>"
+        call popup_close(a:winid)
+
+        return 1
+    endif
+
+    return 0
+endfunction
+
 function! s:VimCreate(options) abort
     " default options
     let l:popup_opts = extend({
@@ -164,6 +190,9 @@ function! s:VimCreate(options) abort
     \        get(g:ale_floating_window_border, 4, '+'),
     \        get(g:ale_floating_window_border, 5, '+'),
     \    ],
+    \    'scrollbar': 1,
+    \    'filter': function('ale#floating_preview#PopupFilter'),
+    \    'filtermode': 'n',
     \    'moved': 'any',
     \ }, s:GetPopupOpts())
 

doc/ale.txt

@@ -835,6 +835,36 @@ or |g:ale_floating_preview| is set to `true` or `1`, the hover information
 will show in a floating window. The borders of the floating preview window can
 be customized by setting |g:ale_floating_window_border|.
 
+For Vim with |popupwin|, floating preview windows can be scrolled with the
+keyboard and dismissed with |<Esc>|. The following keys are supported:
+
+  |<C-n>|   - Scroll down one line
+  |<C-p>|   - Scroll up one line
+  |<C-d>|   - Scroll down half a page
+  |<C-u>|   - Scroll up half a page
+  |<Esc>|   - Close the popup
+
+Mouse scroll wheel also works when |'mouse'| is enabled. The filter can be
+overridden via |g:ale_floating_preview_popup_opts| by providing a custom
+`filter` key. For example, to scroll with `j` and `k` instead: >
+
+  function! MyPopupFilter(winid, key) abort
+      if a:key is# 'j'
+          call win_execute(a:winid, "normal! \<C-e>")
+          return 1
+      elseif a:key is# 'k'
+          call win_execute(a:winid, "normal! \<C-y>")
+          return 1
+      elseif a:key is# "\<Esc>"
+          call popup_close(a:winid)
+          return 1
+      endif
+      return 0
+  endfunction
+
+  let g:ale_floating_preview_popup_opts = {'filter': function('MyPopupFilter')}
+<
+
 For Vim 8.1+ terminals, mouse hovering is disabled by default. Enabling
 |balloonexpr| commands in terminals can cause scrolling issues in terminals,
 so ALE will not attempt to show balloons unless |g:ale_set_balloons| is set to

test/test_floating_preview.vader

@@ -91,3 +91,36 @@ Execute(Floating preview is not used with ALEDetail by default):
   ALEDetail
 
   AssertEqual 0, g:floating_preview_show_called
+
+Execute(PopupFilter should handle scroll down keys):
+  runtime autoload/ale/floating_preview.vim
+
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<C-n>")
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<ScrollWheelDown>")
+
+Execute(PopupFilter should handle scroll up keys):
+  runtime autoload/ale/floating_preview.vim
+
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<C-p>")
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<ScrollWheelUp>")
+
+Execute(PopupFilter should handle page scroll keys):
+  runtime autoload/ale/floating_preview.vim
+
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<C-d>")
+  AssertEqual 1, ale#floating_preview#PopupFilter(0, "\<C-u>")
+
+Execute(PopupFilter should handle Escape to close):
+  runtime autoload/ale/floating_preview.vim
+
+  if has('popupwin')
+    let l:popup_id = popup_create(['test'], {})
+    AssertEqual 1, ale#floating_preview#PopupFilter(l:popup_id, "\<Esc>")
+  endif
+
+Execute(PopupFilter should pass through unhandled keys):
+  runtime autoload/ale/floating_preview.vim
+
+  AssertEqual 0, ale#floating_preview#PopupFilter(0, 'j')
+  AssertEqual 0, ale#floating_preview#PopupFilter(0, 'k')
+  AssertEqual 0, ale#floating_preview#PopupFilter(0, 'q')