Add support for lazy loading

autoload/sy.vim

@@ -12,9 +12,7 @@ function! sy#start() abort
     return
   endif
 
-  if !exists('b:sy_path')
-    let b:sy_path = resolve(expand('%:p'))
-  endif
+  let b:sy_path = resolve(expand('%:p'))
 
   if &diff
         \ || !filereadable(b:sy_path)
@@ -105,7 +103,7 @@ endfunction
 " Function: #toggle {{{1
 function! sy#toggle() abort
   if !exists('b:sy')
-    echomsg 'signify: I cannot sy empty buffers!'
+    call sy#start()
     return
   endif
 

autoload/sy/highlight.vim

@@ -70,11 +70,6 @@ endfunction
 
 " Function: #line_toggle {{{1
 function! sy#highlight#line_toggle() abort
-  if !exists('b:sy')
-    echomsg 'signify: I cannot detect any changes!'
-    return
-  endif
-
   if get(g:, 'signify_line_highlight')
     call sy#highlight#line_disable()
   else
@@ -83,3 +78,6 @@ function! sy#highlight#line_toggle() abort
 
   call sy#start()
 endfunction
+" }}}
+
+call sy#highlight#setup()

plugin/signify.vim

@@ -14,10 +14,8 @@ let g:signify_locked = 0
 augroup signify
   autocmd!
 
-  autocmd VimEnter                         * call sy#highlight#setup()
-  autocmd BufRead,BufEnter,SessionLoadPost * let b:sy_path = resolve(expand('<afile>:p'))
-  autocmd BufRead,BufWritePost             * call sy#start()
-  autocmd BufDelete                        * call sy#stop()
+  autocmd BufRead,BufWritePost * call sy#start()
+  autocmd BufDelete            * call sy#stop()
 
   autocmd QuickFixCmdPre  *vimgrep* let g:signify_locked = 1
   autocmd QuickFixCmdPost *vimgrep* let g:signify_locked = 0