Treat ale_open_list integer values as thresholds (#4050)

Only open list window if the number of warnings or errors equals to or
exceeds the value of ale_open_list. No change when set to `1`.

Co-authored-by: cos <cos>

autoload/ale/list.vim

@@ -36,12 +36,22 @@ function! ale#list#IsQuickfixOpen() abort
 endfunction
 
 " Check if we should open the list, based on the save event being fired, and
-" that setting being on, or the setting just being set to `1`.
-function! s:ShouldOpen(buffer) abort
+" that setting being on, or that the error count is at least as high as the
+" setting when set to an integer value.
+function! s:ShouldOpen(buffer, loclist_len) abort
     let l:val = ale#Var(a:buffer, 'open_list')
     let l:saved = getbufvar(a:buffer, 'ale_save_event_fired', 0)
 
-    return l:val is 1 || (l:val is# 'on_save' && l:saved)
+    return l:val > 0 ? a:loclist_len >= l:val : l:val is# 'on_save' && l:saved
+endfunction
+
+" Check if we should close the list, based on the save event being fired, and
+" that setting being on, or the setting just being set to an integer value.
+function! s:ShouldClose(buffer) abort
+    let l:val = ale#Var(a:buffer, 'open_list')
+    let l:saved = getbufvar(a:buffer, 'ale_save_event_fired', 0)
+
+    return !((l:val >= 1) || (l:val is# 'on_save' && l:saved))
 endfunction
 
 function! s:Deduplicate(list) abort
@@ -122,9 +132,9 @@ function! s:SetListsImpl(timer_id, buffer, loclist) abort
 
     " Open a window to show the problems if we need to.
     "
-    " We'll check if the current buffer's List is not empty here, so the
-    " window will only be opened if the current buffer has problems.
-    if s:ShouldOpen(a:buffer) && !empty(a:loclist)
+    " ShouldOpen() checks if the current buffer has enough problems to be
+    " opened.
+    if s:ShouldOpen(a:buffer, len(a:loclist))
         let l:winnr = winnr()
         let l:mode = mode()
 
@@ -230,7 +240,7 @@ function! ale#list#ForcePopulateErrorList(populate_quickfix) abort
 endfunction
 
 function! s:CloseWindowIfNeeded(buffer) abort
-    if ale#Var(a:buffer, 'keep_list_window_open') || !s:ShouldOpen(a:buffer)
+    if ale#Var(a:buffer, 'keep_list_window_open') || s:ShouldClose(a:buffer)
         return
     endif
 

doc/ale.txt

@@ -1797,6 +1797,9 @@ g:ale_open_list                                               *g:ale_open_list*
   loclist (|lopen|) or for the quickfix list instead if |g:ale_set_quickfix|
   is `1`. (|copen|)
 
+  When set to any higher numberical value, ALE will only open the window when
+  the number of warnings or errors are at least that many.
+
   When set to `'on_save'`, ALE will only open the loclist after buffers have
   been saved. The list will be opened some time after buffers are saved and
   any linter for a buffer returns results.

test/test_list_opening.vader

@@ -97,6 +97,34 @@ Execute(The quickfix window should open for just the loclist):
   call ale#list#SetLists(bufnr('%'), [])
   Assert !ale#list#IsQuickfixOpen()
 
+Execute(The quickfix window should open on the correct threshold):
+  " The window should open for a value lower than number of entries.
+  let g:ale_open_list = len(g:loclist) - 1
+  call ale#list#SetLists(bufnr('%'), g:loclist)
+  Assert ale#list#IsQuickfixOpen()
+
+  " Clear the list to be ready for a new value.
+  call ale#list#SetLists(bufnr('%'), [])
+  Assert !ale#list#IsQuickfixOpen()
+
+  " It should also open for a value equal to the number of entries.
+  let g:ale_open_list = len(g:loclist)
+  call ale#list#SetLists(bufnr('%'), g:loclist)
+  Assert ale#list#IsQuickfixOpen()
+
+  " Clear the list again, preparing for a final value.
+  call ale#list#SetLists(bufnr('%'), [])
+  Assert !ale#list#IsQuickfixOpen()
+
+  " Window should not open for values higher than number of loclist entries.
+  let g:ale_open_list = len(g:loclist) + 1
+  call ale#list#SetLists(bufnr('%'), g:loclist)
+  Assert !ale#list#IsQuickfixOpen()
+
+  " Clear the list just to clean up.
+  call ale#list#SetLists(bufnr('%'), [])
+  Assert !ale#list#IsQuickfixOpen()
+
 Execute(The quickfix window height should be correct for the loclist):
   let g:ale_open_list = 1
   let g:ale_list_window_size = 7