make sets.bzl compatible with --incompatible_depset_is_not_iterable (#71)

lib/sets.bzl

@@ -43,6 +43,20 @@ def _precondition_only_sets_or_lists(*args):
             fail("Expected arguments to be depset or list, but found type %s: %r" %
                  (t, a))
 
+def _depset_to_list(val):
+    """Converts a depset to a list.
+
+    If the given value is a depset, will return the list representation of
+    the depset. Otherwise, will return the value itself.
+
+    Args:
+      val: The value to be optionally converted and returned.
+    """
+    if type(val) == _depset_type:
+        return val.to_list()
+    else:
+        return val
+
 def _is_equal(a, b):
     """Returns whether two sets are equal.
 
@@ -54,7 +68,11 @@ def _is_equal(a, b):
       True if `a` is equal to `b`, False otherwise.
     """
     _precondition_only_sets_or_lists(a, b)
-    return sorted(depset(a)) == sorted(depset(b))
+
+    # Convert both values to a depset then back to a list to remove duplicates.
+    a = _depset_to_list(depset(a))
+    b = _depset_to_list(depset(b))
+    return sorted(a) == sorted(b)
 
 def _is_subset(a, b):
     """Returns whether `a` is a subset of `b`.
@@ -67,8 +85,8 @@ def _is_subset(a, b):
       True if `a` is a subset of `b`, False otherwise.
     """
     _precondition_only_sets_or_lists(a, b)
-    for e in a:
-        if e not in b:
+    for e in _depset_to_list(a):
+        if e not in _depset_to_list(b):
             return False
     return True
 
@@ -85,8 +103,8 @@ def _disjoint(a, b):
       True if `a` and `b` are disjoint, False otherwise.
     """
     _precondition_only_sets_or_lists(a, b)
-    for e in a:
-        if e in b:
+    for e in _depset_to_list(a):
+        if e in _depset_to_list(b):
             return False
     return True
 
@@ -101,7 +119,7 @@ def _intersection(a, b):
       A set containing the elements that are in both `a` and `b`.
     """
     _precondition_only_sets_or_lists(a, b)
-    return depset([e for e in a if e in b])
+    return depset([e for e in _depset_to_list(a) if e in _depset_to_list(b)])
 
 def _union(*args):
     """Returns the union of several sets.
@@ -127,7 +145,7 @@ def _difference(a, b):
       A set containing the elements that are in `a` but not in `b`.
     """
     _precondition_only_sets_or_lists(a, b)
-    return depset([e for e in a if e not in b])
+    return depset([e for e in _depset_to_list(a) if e not in _depset_to_list(b)])
 
 sets = struct(
     difference = _difference,