lib/selects.bzl

# Copyright 2017 The Bazel Authors. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
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"""Skylib module containing convenience interfaces for select()."""

def _with_or(input_dict, no_match_error = ""):
    """Drop-in replacement for `select()` that supports ORed keys.

    Args:
      input_dict: The same dictionary `select()` takes, except keys may take
          either the usual form `"//foo:config1"` or
          `("//foo:config1", "//foo:config2", ...)` to signify
          `//foo:config1` OR `//foo:config2` OR `...`.
      no_match_error: Optional custom error to report if no condition matches.

          Example:

          ```build
          deps = selects.with_or({
              "//configs:one": [":dep1"],
              ("//configs:two", "//configs:three"): [":dep2or3"],
              "//configs:four": [":dep4"],
              "//conditions:default": [":default"]
          })
          ```

          Key labels may appear at most once anywhere in the input.

    Returns:
      A native `select()` that expands

      `("//configs:two", "//configs:three"): [":dep2or3"]`

      to

      ```build
      "//configs:two": [":dep2or3"],
      "//configs:three": [":dep2or3"],
      ```
    """
    return select(_with_or_dict(input_dict), no_match_error = no_match_error)

def _with_or_dict(input_dict):
    """Variation of `with_or` that returns the dict of the `select()`.

    Unlike `select()`, the contents of the dict can be inspected by Starlark
    macros.

    Args:
      input_dict: Same as `with_or`.

    Returns:
      A dictionary usable by a native `select()`.
    """
    output_dict = {}
    for (key, value) in input_dict.items():
        if type(key) == type(()):
            for config_setting in key:
                if config_setting in output_dict.keys():
                    fail("key %s appears multiple times" % config_setting)
                output_dict[config_setting] = value
        else:
            if key in output_dict.keys():
                fail("key %s appears multiple times" % key)
            output_dict[key] = value
    return output_dict

selects = struct(
    with_or = _with_or,
    with_or_dict = _with_or_dict,
)