Add simple logging.

.gitignore

@@ -1,3 +1,5 @@
 /doc/tags
 /misc
 /test/*.actual
+gitgutter.log
+

autoload/gitgutter.vim

@@ -25,6 +25,7 @@ function! gitgutter#process_buffer(bufnr, realtime)
         endif
       endif
     catch /diff failed/
+      call gitgutter#debug#log('diff failed')
       call gitgutter#hunk#reset()
     endtry
   else
@@ -34,6 +35,8 @@ endfunction
 
 
 function! gitgutter#handle_diff_job(job_id, data, event)
+  call gitgutter#debug#log('job_id: '.a:job_id.', event: '.a:event)
+
   if a:event == 'stdout'
     " a:data is a list
     call gitgutter#utility#job_output_received(a:job_id, 'stdout')
@@ -56,6 +59,8 @@ endfunction
 
 
 function! gitgutter#handle_diff(diff)
+  call gitgutter#debug#log(a:diff)
+
   call setbufvar(gitgutter#utility#bufnr(), 'gitgutter_tracked', 1)
 
   call gitgutter#hunk#set_hunks(gitgutter#diff#parse_diff(a:diff))

autoload/gitgutter/debug.vim

@@ -1,3 +1,5 @@
+let s:log_file = expand('<sfile>:p:h:h:h').'/'.'gitgutter.log'
+
 function! gitgutter#debug#debug()
   " Open a scratch buffer
   vsplit __GitGutter_Debug__
@@ -70,8 +72,19 @@ function! gitgutter#debug#output(text)
   call append(line('$'), a:text)
 endfunction
 
-function! gitgutter#debug#log(message)
-  let msg = type(a:message) == 1 ? split(a:message, '\n') : a:message
-  call writefile(msg, 'gitgutter.log', 'a')
+" assumes optional args are calling function's optional args
+function! gitgutter#debug#log(message, ...)
+  if g:gitgutter_log
+    execute 'redir >> '.s:log_file
+      " callers excluding this function
+      silent echo "\n".expand('<sfile>')[:-22].':'
+      silent echo type(a:message) == 1 ? join(split(a:message, '\n'),"\n") : a:message
+      if a:0 && !empty(a:1)
+        for msg in a:000
+          silent echo type(msg) == 1 ? join(split(msg, '\n'),"\n") : msg
+        endfor
+      endif
+    redir END
+  endif
 endfunction
 

autoload/gitgutter/diff.vim

@@ -134,9 +134,11 @@ function! gitgutter#diff#run_diff(realtime, preserve_full_diff)
           \ 'on_stderr': function('gitgutter#handle_diff_job'),
           \ 'on_exit':   function('gitgutter#handle_diff_job')
           \ })
+    call gitgutter#debug#log('[job_id: '.job_id.'] '.cmd)
     if job_id < 1
       throw 'diff failed'
     endif
+
     call gitgutter#utility#pending_job(job_id)
     return 'async'
   else

autoload/gitgutter/utility.vim

@@ -121,6 +121,8 @@ function! gitgutter#utility#using_xolox_shell()
 endfunction
 
 function! gitgutter#utility#system(cmd, ...)
+  call gitgutter#debug#log(a:cmd, a:000)
+
   if gitgutter#utility#using_xolox_shell()
     let options = {'command': a:cmd, 'check': 0}
     if a:0 > 0

plugin/gitgutter.vim

@@ -50,6 +50,7 @@ call s:set('g:gitgutter_diff_base',                  '')
 call s:set('g:gitgutter_map_keys',                    1)
 call s:set('g:gitgutter_avoid_cmd_prompt_on_windows', 1)
 call s:set('g:gitgutter_async',                       1)
+call s:set('g:gitgutter_log',                         0)
 
 call gitgutter#highlight#define_sign_column_highlight()
 call gitgutter#highlight#define_highlights()