index: rename _fix_index() since it no longer fixes the index

Since c0d411ea6639 (index: drop support for negative indexes into the
index, 2018-07-20), it always returns the input (unless it raises).

Differential Revision: https://phab.mercurial-scm.org/D4334

mercurial/pure/parsers.py

@@ -44,17 +44,16 b' class BaseIndexObject(object):'
     def append(self, tup):
         self._extra.append(tup)
 
-    def _fix_index(self, i):
+    def _check_index(self, i):
         if not isinstance(i, int):
             raise TypeError("expecting int indexes")
         if i < 0 or i >= len(self):
             raise IndexError
-        return i
 
     def __getitem__(self, i):
         if i == -1:
             return (0, 0, 0, -1, -1, -1, -1, nullid)
-        i = self._fix_index(i)
+        self._check_index(i)
         if i >= self._lgt:
             return self._extra[i - self._lgt]
         index = self._calculate_index(i)
@@ -79,7 +78,8 b' class IndexObject(BaseIndexObject):'
     def __delitem__(self, i):
         if not isinstance(i, slice) or not i.stop == -1 or i.step is not None:
             raise ValueError("deleting slices only supports a:-1 with step 1")
-        i = self._fix_index(i.start)
+        i = i.start
+        self._check_index(i)
         if i < self._lgt:
             self._data = self._data[:i * indexsize]
             self._lgt = i
@@ -113,7 +113,8 b' class InlinedIndexObject(BaseIndexObject'
     def __delitem__(self, i):
         if not isinstance(i, slice) or not i.stop == -1 or i.step is not None:
             raise ValueError("deleting slices only supports a:-1 with step 1")
-        i = self._fix_index(i.start)
+        i = i.start
+        self._check_index(i)
         if i < self._lgt:
             self._offsets = self._offsets[:i]
             self._lgt = i