Fix range in Span.get_lca_matrix (#8115)

Fix the adjusted token index / lca matrix index ranges for
`_get_lca_matrix` for spans.

* The range for `k` should correspond to the adjusted indices in
`lca_matrix` with the `start` indexed at `0`

spacy/tests/doc/test_span.py

@@ -2,6 +2,8 @@
 from __future__ import unicode_literals
 
 import pytest
+import numpy
+from numpy.testing import assert_array_equal
 from spacy.attrs import ORTH, LENGTH
 from spacy.tokens import Doc, Span
 from spacy.vocab import Vocab
@@ -118,6 +120,14 @@ def test_spans_lca_matrix(en_tokenizer):
     assert lca[1, 0] == 1  # slept & dog -> slept
     assert lca[1, 1] == 1  # slept & slept -> slept
 
+    # example from Span API docs
+    tokens = en_tokenizer("I like New York in Autumn")
+    doc = get_doc(
+        tokens.vocab, words=[t.text for t in tokens], heads=[1, 0, 1, -2, -1, -1]
+    )
+    lca = doc[1:4].get_lca_matrix()
+    assert_array_equal(lca, numpy.asarray([[0, 0, 0], [0, 1, 2], [0, 2, 2]]))
+
 
 def test_span_similarity_match():
     doc = Doc(Vocab(), words=["a", "b", "a", "b"])

spacy/tokens/doc.pyx

@@ -1351,7 +1351,7 @@ cdef int [:,:] _get_lca_matrix(Doc doc, int start, int end):
         j_idx_in_sent = start + j - sent_start
         n_missing_tokens_in_sent = len(sent) - j_idx_in_sent
         # make sure we do not go past `end`, in cases where `end` < sent.end
-        max_range = min(j + n_missing_tokens_in_sent, end)
+        max_range = min(j + n_missing_tokens_in_sent, end - start)
         for k in range(j + 1, max_range):
             lca = _get_tokens_lca(token_j, doc[start + k])
             # if lca is outside of span, we set it to -1