* Ensure high loss for invalid moves, and fix label reading for arc-eager

spacy/syntax/arc_eager.pyx

@@ -35,14 +35,15 @@ cdef get_cost_func_t[N_MOVES] get_cost_funcs
 cdef class ArcEager(TransitionSystem):
     @classmethod
     def get_labels(cls, gold_parses):
-        labels = {SHIFT: {0: True}, REDUCE: {0: True}, RIGHT: {0: True},
-                  LEFT: {0: True}, BREAK: {0: True}}
+        labels = {SHIFT: {'ROOT': True}, REDUCE: {'ROOT': True}, RIGHT: {},
+                  LEFT: {}, BREAK: {'ROOT': True}}
         for parse in gold_parses:
             for i, (head, label) in enumerate(zip(parse.heads, parse.labels)):
-                if head > i:
-                    labels[RIGHT][label] = True
-                else:
-                    labels[LEFT][label] = True
+                if label != 'ROOT':
+                    if head > i:
+                        labels[RIGHT][label] = True
+                    elif head < i:
+                        labels[LEFT][label] = True
         return labels
 
     cdef Transition init_transition(self, int clas, int move, int label) except *:
@@ -71,6 +72,8 @@ cdef class ArcEager(TransitionSystem):
             if scores[i] > score and is_valid[self.c[i].move]:
                 best = self.c[i]
                 score = scores[i]
+        assert best.clas < self.n_moves
+        assert score > MIN_SCORE
         # Label Shift moves with the best Right-Arc label, for non-monotonic
         # actions
         if best.move == SHIFT:
@@ -85,7 +88,7 @@ cdef class ArcEager(TransitionSystem):
 cdef int _do_shift(const Transition* self, State* state) except -1:
     # Set the dep label, in case we need it after we reduce
     if NON_MONOTONIC:
-        get_s0(state).dep = self.label
+        state.sent[state.i].dep = self.label
     push_stack(state)
 
 
@@ -124,7 +127,8 @@ do_funcs[BREAK] = _do_break
 
 
 cdef int _shift_cost(const Transition* self, const State* s, GoldParse gold) except -1:
-    assert not at_eol(s)
+    if not _can_shift(s):
+        return 9000
     cost = 0
     cost += head_in_stack(s, s.i, gold.c_heads)
     cost += children_in_stack(s, s.i, gold.c_heads)
@@ -137,7 +141,8 @@ cdef int _shift_cost(const Transition* self, const State* s, GoldParse gold) exc
 
 
 cdef int _right_cost(const Transition* self, const State* s, GoldParse gold) except -1:
-    assert s.stack_len >= 1
+    if not _can_right(s):
+        return 9000
     cost = 0
     if gold.c_heads[s.i] == s.stack[0]:
         cost += self.label != gold.c_labels[s.i]
@@ -151,7 +156,8 @@ cdef int _right_cost(const Transition* self, const State* s, GoldParse gold) exc
 
 
 cdef int _left_cost(const Transition* self, const State* s, GoldParse gold) except -1:
-    assert s.stack_len >= 1
+    if not _can_left(s):
+        return 9000
     cost = 0
     if gold.c_heads[s.stack[0]] == s.i:
         cost += self.label != gold.c_labels[s.stack[0]]
@@ -166,6 +172,8 @@ cdef int _left_cost(const Transition* self, const State* s, GoldParse gold) exce
 
 
 cdef int _reduce_cost(const Transition* self, const State* s, GoldParse gold) except -1:
+    if not _can_reduce(s):
+        return 9000
     cdef int cost = 0
     cost += children_in_buffer(s, s.stack[0], gold.c_heads)
     if NON_MONOTONIC:
@@ -174,6 +182,8 @@ cdef int _reduce_cost(const Transition* self, const State* s, GoldParse gold) ex
 
 
 cdef int _break_cost(const Transition* self, const State* s, GoldParse gold) except -1:
+    if not _can_break(s):
+        return 9000
     # When we break, we Reduce all of the words on the stack.
     cdef int cost = 0
     # Number of deps between S0...Sn and N0...Nn