Implement a more efficient statusbar

The statusbar now keeps its state in a separate variable, in order to
avoid excess iterations. The engine now updates said variable on run,
and a new function is made available for external statusbars to call (to
avoid dependencies on internal implementation details of ale).

To keep things light, the status bar code is not loaded unless invoked
by the user or an external plugin. On the first load it will update
itself from the global loclist, after that, the engine will handle all
updates.

The external integration function, `ale#statusline#Count()`, will return
a tuple in the format [E, W] (where E is errors, W is warnings), unless
no data exists (ie, the plugin doesn't have a linter for a file or has
not run yet), in which case it returns 0/false.

5 files changed, 76 insertions, 40 deletions

diff --git a/autoload/ale/cleanup.vim b/autoload/ale/cleanup.vim
index 2f636eee..45eccb98 100644
--- a/autoload/ale/cleanup.vim
+++ b/autoload/ale/cleanup.vim
@@ -2,14 +2,18 @@
 " Description: Utility functions related to cleaning state.
 
 function! ale#cleanup#Buffer(buffer) abort
-    if has_key(g:ale_buffer_should_reset_map, a:buffer)
-        call remove(g:ale_buffer_should_reset_map, a:buffer)
+    if has_key(g:ale_buffer_count_map, a:buffer)
+        call remove(g:ale_buffer_count_map, a:buffer)
     endif
 
     if has_key(g:ale_buffer_loclist_map, a:buffer)
         call remove(g:ale_buffer_loclist_map, a:buffer)
     endif
 
+    if has_key(g:ale_buffer_should_reset_map, a:buffer)
+        call remove(g:ale_buffer_should_reset_map, a:buffer)
+    endif
+
     if has_key(g:ale_buffer_sign_dummy_map, a:buffer)
         call remove(g:ale_buffer_sign_dummy_map, a:buffer)
     endif
diff --git a/autoload/ale/engine.vim b/autoload/ale/engine.vim
index 7342a541..1d0ad3d5 100644
--- a/autoload/ale/engine.vim
+++ b/autoload/ale/engine.vim
@@ -98,7 +98,7 @@ function! s:HandleExit(job) abort
     " Sort the loclist again.
     " We need a sorted list so we can run a binary search against it
     " for efficient lookup of the messages in the cursor handler.
-    call sort(g:ale_buffer_loclist_map[l:buffer], 'ale#util#LocItemCompare')
+    call sort(g:ale_buffer_loclist_map[l:buffer], 's:LocItemCompare')
 
     if g:ale_set_loclist
         call setloclist(0, g:ale_buffer_loclist_map[l:buffer])
@@ -108,6 +108,11 @@ function! s:HandleExit(job) abort
         call ale#sign#SetSigns(l:buffer, g:ale_buffer_loclist_map[l:buffer])
     endif
 
+    if exists('*ale#statusline#Update')
+        " Don't load/run if not already loaded.
+        call ale#statusline#Update(l:buffer, g:ale_buffer_loclist_map[l:buffer])
+    endif
+
     " Mark line 200, column 17 with a squiggly line or something
     " matchadd('ALEError', '\%200l\%17v')
 endfunction
@@ -136,6 +141,26 @@ function! s:FixLocList(buffer, loclist) abort
     endfor
 endfunction
 
+function! s:LocItemCompare(left, right) abort
+    if a:left['lnum'] < a:right['lnum']
+        return -1
+    endif
+
+    if a:left['lnum'] > a:right['lnum']
+        return 1
+    endif
+
+    if a:left['col'] < a:right['col']
+        return -1
+    endif
+
+    if a:left['col'] > a:right['col']
+        return 1
+    endif
+
+    return 0
+endfunction
+
 function! ale#engine#Invoke(buffer, linter) abort
     if has_key(a:linter, 'job')
         " Stop previous jobs for the same linter.
diff --git a/autoload/ale/statusline.vim b/autoload/ale/statusline.vim
index 995fcd94..48a51f19 100644
--- a/autoload/ale/statusline.vim
+++ b/autoload/ale/statusline.vim
@@ -1,20 +1,12 @@
 " Author: KabbAmine <amine.kabb@gmail.com>
 " Description: Statusline related function(s)
 
-function! ale#statusline#Status() abort
-    " Returns a formatted string that can be integrated in the
-    " statusline
-
-    let l:buffer = bufnr('%')
-    let l:loclist = g:ale_buffer_loclist_map
-
-    if !has_key(l:loclist, l:buffer)
-        return ''
-    endif
-
+" Update the buffer error/warning count with data from loclist.
+function! ale#statusline#Update(buffer, loclist) abort
     let l:errors = 0
     let l:warnings = 0
-    for l:entry in l:loclist[l:buffer]
+
+    for l:entry in a:loclist
         if l:entry.type ==# 'E'
             let l:errors += 1
         else
@@ -22,8 +14,41 @@ function! ale#statusline#Status() abort
         endif
     endfor
 
-    let l:errors = l:errors ? printf(g:ale_statusline_format[0], l:errors) : ''
-    let l:warnings = l:warnings ? printf(g:ale_statusline_format[1], l:warnings) : ''
+    let g:ale_buffer_count_map[a:buffer] = [l:errors, l:warnings]
+endfunction
+
+" Returns a tuple of errors and warnings (or false if no data exists)
+" for use in third-party integrations.
+function! ale#statusline#Count(buffer) abort
+    if !has_key(g:ale_buffer_count_map, a:buffer)
+        if has_key(g:ale_buffer_loclist_map, a:buffer)
+            call ale#statusline#Update(a:buffer, g:ale_buffer_loclist_map[a:buffer])
+            return ale#statusline#Count(a:buffer)
+        else
+            return 0
+        endif
+    endif
+
+    return g:ale_buffer_count_map[a:buffer]
+endfunction
+
+" Returns a formatted string that can be integrated in the statusline.
+function! ale#statusline#Status() abort
+    let l:buffer = bufnr('%')
+
+    if !has_key(g:ale_buffer_count_map, l:buffer)
+        if has_key(g:ale_buffer_loclist_map, l:buffer)
+            call ale#statusline#Update(l:buffer, g:ale_buffer_loclist_map[l:buffer])
+            return ale#statusline#Status()
+        else
+            return ''
+        endif
+    endif
+
+    let l:errors = g:ale_buffer_count_map[l:buffer][0] ?
+      \ printf(g:ale_statusline_format[0], g:ale_buffer_count_map[l:buffer][0]) : ''
+    let l:warnings = g:ale_buffer_count_map[l:buffer][1] ?
+      \ printf(g:ale_statusline_format[1], g:ale_buffer_count_map[l:buffer][1]) : ''
     let l:no_errors = g:ale_statusline_format[2]
 
     " Different formats if no errors or no warnings
diff --git a/autoload/ale/util.vim b/autoload/ale/util.vim
index 17ce7c44..4217ac49 100644
--- a/autoload/ale/util.vim
+++ b/autoload/ale/util.vim
@@ -43,23 +43,3 @@ function! ale#util#GetFunction(string_or_ref) abort
 
     return a:string_or_ref
 endfunction
-
-function! ale#util#LocItemCompare(left, right) abort
-    if a:left['lnum'] < a:right['lnum']
-        return -1
-    endif
-
-    if a:left['lnum'] > a:right['lnum']
-        return 1
-    endif
-
-    if a:left['col'] < a:right['col']
-        return -1
-    endif
-
-    if a:left['col'] > a:right['col']
-        return 1
-    endif
-
-    return 0
-endfunction
diff --git a/plugin/ale.vim b/plugin/ale.vim
index 9b45cd7c..d1c29902 100644
--- a/plugin/ale.vim
+++ b/plugin/ale.vim
@@ -24,6 +24,7 @@ endif
 
 " Globals
 
+let g:ale_buffer_count_map = {}
 let g:ale_buffer_loclist_map = {}
 let g:ale_buffer_should_reset_map = {}
 let g:ale_buffer_sign_dummy_map = {}
@@ -98,7 +99,8 @@ let g:ale_echo_msg_error_str = get(g:, 'ale_echo_msg_error_str', 'Error')
 let g:ale_echo_msg_warning_str = get(g:, 'ale_echo_msg_warning_str', 'Warning')
 
 " This flag can be set to 0 to disable echoing when the cursor moves.
-if get(g:, 'ale_echo_cursor', 1)
+let g:ale_echo_cursor = get(g:, 'ale_echo_cursor', 1)
+if g:ale_echo_cursor
     augroup ALECursorGroup
         autocmd!
         autocmd CursorMoved,CursorHold * call ale#cursor#EchoCursorWarningWithDelay()
@@ -120,10 +122,10 @@ let g:ale_warn_about_trailing_whitespace =
 
 " Housekeeping
 
-augroup ALECleanup
+augroup ALECleanupGroup
     autocmd!
     " Clean up buffers automatically when they are unloaded.
-    autocmd BufUnload * call ale#cleanup#Buffer('<abuf>')
+    autocmd BufUnload * call ale#cleanup#Buffer(expand('<abuf>'))
 augroup END
 
 " Backwards Compatibility