add _dependencies_sans_invariants

nutils/evaluable.py

@@ -3329,10 +3329,7 @@ def __init__(self, funcdata:prepare_funcdata, index:types.strict[Argument], leng
     self.func = funcdata[0]
     self.index = index
     self.length = length
-    self._invariants = []
-    self._dependencies = []
-    _populate_dependencies_sans_invariants(self.func, index, self._invariants, self._dependencies, set())
-    assert (self._dependencies or self._invariants or [index])[-1] == self.func
+    self._invariants, self._dependencies = _dependencies_sans_invariants(self.func, index)
     axes = tuple(Axis(axis.length) if isinstance(axis, Sparse) else axis for axis in self.func._axes)
     super().__init__(args=(shape, length, *self._invariants), shape=axes, dtype=self.func.dtype)
 
@@ -3521,11 +3518,8 @@ def __init__(self, funcdatas:types.tuple[asarrays], index:types.strict[Argument]
       raise ValueError('the length of the loop must not depend on the index')
     self._index = index
     self._length = length
-    self._invariants = []
-    self._dependencies = []
-    result = Tuple([Tuple([start, stop, func]) for func, start, stop, *shape in funcdatas])
-    _populate_dependencies_sans_invariants(result, index, self._invariants, self._dependencies, set())
-    assert (self._dependencies or self._invariants)[-1] == result
+    self._invariants, self._dependencies = _dependencies_sans_invariants(
+      Tuple([Tuple([start, stop, func]) for func, start, stop, *shape in funcdatas]), index)
     super().__init__(args=(Tuple(shapes), length, *self._invariants))
 
   @property
@@ -3641,13 +3635,18 @@ def _inflate_scalar(arg, shape):
 def _isunique(array):
   return numpy.unique(array).size == array.size
 
+def _dependencies_sans_invariants(func, arg):
+  invariants = []
+  dependencies = []
+  _populate_dependencies_sans_invariants(func, arg, invariants, dependencies, {arg})
+  assert (dependencies or invariants or [arg])[-1] == func
+  return tuple(invariants), tuple(dependencies)
+
 def _populate_dependencies_sans_invariants(func, arg, invariants, dependencies, cache):
   if func in cache:
     return
   cache.add(func)
-  if func == arg:
-    pass
-  elif arg in func.arguments:
+  if arg in func.arguments:
     for child in func._Evaluable__args:
       _populate_dependencies_sans_invariants(child, arg, invariants, dependencies, cache)
     dependencies.append(func)