Optimize ale#completion#Filter when prefix is ""

autoload/ale/completion.vim

@@ -89,6 +89,10 @@ function! ale#completion#GetPrefix(filetype, line, column) abort
 endfunction
 
 function! ale#completion#GetTriggerCharacter(filetype, prefix) abort
+    if empty(a:prefix)
+        return ''
+    endif
+
     let l:char_list = s:GetFiletypeValue(s:trigger_character_map, a:filetype)
 
     if index(l:char_list, a:prefix) >= 0
@@ -100,33 +104,38 @@ endfunction
 
 function! ale#completion#Filter(buffer, filetype, suggestions, prefix) abort
     let l:excluded_words = ale#Var(a:buffer, 'completion_excluded_words')
-    let l:triggers = s:GetFiletypeValue(s:trigger_character_map, a:filetype)
 
-    " For completing...
-    "   foo.
-    "       ^
-    " We need to include all of the given suggestions.
-    if index(l:triggers, a:prefix) >= 0 || empty(a:prefix)
+    if empty(a:prefix)
         let l:filtered_suggestions = a:suggestions
     else
-        let l:filtered_suggestions = []
+        let l:triggers = s:GetFiletypeValue(s:trigger_character_map, a:filetype)
 
-        " Filter suggestions down to those starting with the prefix we used for
-        " finding suggestions in the first place.
-        "
-        " Some completion tools will include suggestions which don't even start
-        " with the characters we have already typed.
-        for l:item in a:suggestions
-            " A List of String values or a List of completion item Dictionaries
-            " is accepted here.
-            let l:word = type(l:item) is v:t_string ? l:item : l:item.word
+        " For completing...
+        "   foo.
+        "       ^
+        " We need to include all of the given suggestions.
+        if index(l:triggers, a:prefix) >= 0 || empty(a:prefix)
+            let l:filtered_suggestions = a:suggestions
+        else
+            let l:filtered_suggestions = []
 
-            " Add suggestions if the suggestion starts with a case-insensitive
-            " match for the prefix.
-            if l:word[: len(a:prefix) - 1] is? a:prefix
-                call add(l:filtered_suggestions, l:item)
-            endif
-        endfor
+            " Filter suggestions down to those starting with the prefix we
+            " used for finding suggestions in the first place.
+            "
+            " Some completion tools will include suggestions which don't even
+            " start with the characters we have already typed.
+            for l:item in a:suggestions
+                " A List of String values or a List of completion item
+                " Dictionaries is accepted here.
+                let l:word = type(l:item) is v:t_string ? l:item : l:item.word
+
+                " Add suggestions if the suggestion starts with a
+                " case-insensitive match for the prefix.
+                if l:word[: len(a:prefix) - 1] is? a:prefix
+                    call add(l:filtered_suggestions, l:item)
+                endif
+            endfor
+        endif
     endif
 
     if !empty(l:excluded_words)
@@ -514,13 +523,12 @@ endfunction
 
 " This function can be used to manually trigger autocomplete, even when
 " g:ale_completion_enabled is set to false
-function! ale#completion#AlwaysGetCompletions(...) abort
-    let l:need_prefix = get(a:, 1, 0)
+function! ale#completion#AlwaysGetCompletions(need_prefix) abort
     let [l:line, l:column] = getcurpos()[1:2]
 
     let l:prefix = ale#completion#GetPrefix(&filetype, l:line, l:column)
 
-    if l:need_prefix && empty(l:prefix)
+    if a:need_prefix && empty(l:prefix)
         return
     endif
 

plugin/ale.vim

@@ -204,7 +204,7 @@ command! -bar ALEDocumentation :call ale#hover#ShowDocumentationAtCursor()
 " Search for appearances of a symbol, such as a type name or function name.
 command! -nargs=1 ALESymbolSearch :call ale#symbol#Search(<q-args>)
 
-command! -bar ALEComplete :call ale#completion#AlwaysGetCompletions()
+command! -bar ALEComplete :call ale#completion#AlwaysGetCompletions(0)
 
 " <Plug> mappings for commands
 nnoremap <silent> <Plug>(ale_previous) :ALEPrevious<Return>

test/completion/test_completion_filtering.vader

@@ -105,6 +105,9 @@ Execute(Excluding words from completion results should work with lists of String
   AssertEqual
   \ ['Deutsch'],
   \ ale#completion#Filter(bufnr(''), '', ['describe', 'Deutsch'], '.')
+  AssertEqual
+  \ ['Deutsch'],
+  \ ale#completion#Filter(bufnr(''), '', ['Deutsch'], '')
 
 Execute(Filtering shouldn't modify the original list):
   let b:ale_completion_excluded_words = ['it', 'describe']

test/test_ale_complete_command.vader

@@ -1,9 +1,11 @@
 Before:
   function! MockAlwaysGetCompletions() abort
     let g:get_completions_called = 0
+    let g:always_get_completions_argument = -1
 
-    function! ale#completion#AlwaysGetCompletions() abort
+    function! ale#completion#AlwaysGetCompletions(need_prefix) abort
       let g:get_completions_called = 1
+      let g:always_get_completions_argument = a:need_prefix
     endfunction
   endfunction
 
@@ -11,6 +13,7 @@ Before:
 
 After:
   unlet! g:get_completions_called
+  unlet! g:always_get_completions_argument
   delfunction MockAlwaysGetCompletions
   delfunction ale#completion#AlwaysGetCompletions
 
@@ -20,3 +23,4 @@ Execute(ale#completion#AlwaysGetCompletions should be called when ALEComplete is
   AssertEqual 0, g:get_completions_called
   ALEComplete
   AssertEqual 1, g:get_completions_called
+  AssertEqual 0, g:always_get_completions_argument