Rewind the first time new text is inserted in the processed region

The CursorMovedI event is triggered when new text is inserted, which is better
than InsertEnter that would resync the buffer on the next insert.

Also fix an off by one error around changing the last character in a statement,
or jumping to the last character in a statement.

autoload/coquille.py

@@ -111,7 +111,8 @@ def sync(self):
                 self._reset()
         else:
             (line, col) = self.saved_sync.pos()
-            self.rewind_to(line - 1, col) # vim indexes from lines 1, coquille from 0
+            # vim indexes from lines 1, coquille from 0
+            self.rewind_to(line - 1, col - 1)
         self.saved_sync = curr_sync
 
     def _reset(self):
@@ -173,7 +174,9 @@ def coq_to_cursor(self):
                              else self.coq_top.states[-1].end)
 
         if cline < line or (cline == line and ccol < col):
-            self.rewind_to(cline - 1, ccol)
+            # Add 1 to the column to leave whatever is at the
+            # cursor as sent.
+            self.rewind_to(cline - 1, ccol + 1)
         else:
             while True:
                 r = self._get_message_range((line, col))
@@ -422,12 +425,25 @@ def reset_color(self):
                     self.source_buffer.number)
 
     def rewind_to(self, line, col):
+        """ Go backwards to the specified position
+
+        line and col are 0-based and point to the first position to
+        remove from the sent region.
+        """
+        print("rewinding to", line, col)
+        print("last state", self.coq_top.states[-1].end)
         if self.coq_top.coqtop is None:
             print('Internal error: vimbufsync is still being called but coqtop\
                     appears to be down.')
             print('Please report.')
             return
 
+        if self.coq_top.states and self.coq_top.states[-1].end <= (line, col):
+            # The caller asked to rewind to a position after what has been
+            # processed. This quick path exits without having to search the
+            # state list.
+            return
+
         predicate = lambda x: x.end <= (line, col)
         lst = filter(predicate, self.coq_top.states)
         steps = len(self.coq_top.states) - len(list(lst))

autoload/coquille.vim

@@ -202,14 +202,16 @@ function! coquille#OpenSupportingBuffers(bufid, ...)
         call setbufvar(a:bufid, "errors", -1)
         execute "autocmd BufUnload <buffer=" . a:bufid .
                     \ "> call coquille#DetachSupportingBuffers(". a:bufid .")"
-        " Automatically sync the buffer when entering insert mode: this is usefull
-        " when we edit the portion of the buffer which has already been sent to coq,
-        " we can then rewind to the appropriate point.
-        " It's still incomplete though, the plugin won't sync when you undo or
-        " delete some part of your buffer. So the highlighting will be wrong, but
-        " nothing really problematic will happen, as sync will be called the next
-        " time you explicitly call a command (be it 'rewind' or 'interp')
-        execute "autocmd InsertEnter <buffer=" . a:bufid .
+        " Automatically sync the buffer when the cursor moves while in insert
+        " mode. Typically this happens when the buffer is modified. Syncing
+        " the buffer is useful when we edit the portion of the buffer which
+        " has already been sent to coq, we can then rewind to the appropriate
+        " point.  It's still incomplete though, the plugin won't sync when you
+        " undo or delete some part of your buffer. So the highlighting will be
+        " wrong, but nothing really problematic will happen, as sync will be
+        " called the next time you explicitly call a command (be it 'rewind'
+        " or 'interp')
+        execute "autocmd CursorMovedI <buffer=" . a:bufid .
                     \ "> call coquille#Python('"
                     \ "coquille.BufferState.lookup_bufid(".
                     \ a:bufid . ").sync()')"