140 lines
3.9 KiB
Python
140 lines
3.9 KiB
Python
# Copyright 2017 The Bazel Authors. All rights reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Skylib module containing common set algorithms.
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CAUTION: Operating on sets, particularly sets contained in providers, may
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asymptotically slow down the analysis phase. While constructing large sets with
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addition/union is fast (there is no linear-time copy involved), the
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`difference` function and various comparison predicates involve linear-time
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traversals.
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For convenience, the functions in this module can take either sets or lists as
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inputs; operations that take lists treat them as if they were sets (i.e.,
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duplicate elements are ignored). Functions that return new sets always return
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them as the `set` type, regardless of the types of the inputs.
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"""
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_depset_type = type(depset())
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_list_type = type([])
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def _precondition_only_sets_or_lists(*args):
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"""Verifies that all arguments are either sets or lists.
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The build will fail if any of the arguments is neither a set nor a list.
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Args:
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*args: A list of values that must be sets or lists.
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"""
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for a in args:
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t = type(a)
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if t not in (_depset_type, _list_type):
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fail("Expected arguments to be depset or list, but found type %s: %r" %
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(t, a))
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def _is_equal(a, b):
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"""Returns whether two sets are equal.
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Args:
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a: A depset or a list.
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b: A depset or a list.
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Returns:
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True if `a` is equal to `b`, False otherwise.
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"""
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_precondition_only_sets_or_lists(a, b)
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return sorted(depset(a)) == sorted(depset(b))
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def _is_subset(a, b):
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"""Returns whether `a` is a subset of `b`.
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Args:
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a: A depset or a list.
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b: A depset or a list.
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Returns:
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True if `a` is a subset of `b`, False otherwise.
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"""
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_precondition_only_sets_or_lists(a, b)
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for e in a:
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if e not in b:
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return False
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return True
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def _disjoint(a, b):
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"""Returns whether two sets are disjoint.
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Two sets are disjoint if they have no elements in common.
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Args:
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a: A set or list.
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b: A set or list.
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Returns:
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True if `a` and `b` are disjoint, False otherwise.
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"""
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_precondition_only_sets_or_lists(a, b)
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for e in a:
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if e in b:
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return False
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return True
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def _intersection(a, b):
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"""Returns the intersection of two sets.
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Args:
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a: A set or list.
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b: A set or list.
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Returns:
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A set containing the elements that are in both `a` and `b`.
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"""
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_precondition_only_sets_or_lists(a, b)
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return depset([e for e in a if e in b])
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def _union(*args):
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"""Returns the union of several sets.
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Args:
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*args: An arbitrary number of sets or lists.
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Returns:
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The set union of all sets or lists in `*args`.
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"""
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_precondition_only_sets_or_lists(*args)
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args_deps = [depset(x) if type(x) == _list_type else x for x in args]
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return depset(transitive = args_deps)
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def _difference(a, b):
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"""Returns the elements in `a` that are not in `b`.
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Args:
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a: A set or list.
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b: A set or list.
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Returns:
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A set containing the elements that are in `a` but not in `b`.
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"""
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_precondition_only_sets_or_lists(a, b)
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return depset([e for e in a if e not in b])
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sets = struct(
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difference = _difference,
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disjoint = _disjoint,
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intersection = _intersection,
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is_equal = _is_equal,
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is_subset = _is_subset,
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union = _union,
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)
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