ceph/src/boost/tools/build/src/tools/features/relevant-feature.jam

   1 # Copyright 2017 Steven Watanabe
   2 # Distributed under the Boost Software License, Version 1.0.
   3 # (See accompanying file LICENSE_1_0.txt or copy at
   4 # http://www.boost.org/LICENSE_1_0.txt)
   5
   6 import feature ;
   7
   8 #| tag::doc[]
   9
  10 [[bbv2.builtin.features.relevant]]`relevant`::
  11 *Allowed values:* the name of any feature.
  12 +
  13 Indicates which other features are relevant for a given target. It is usually
  14 not necessary to manage it explicitly, as B2 can deduce it in most
  15 cases. Features which are not relevant will not affect target paths, and will
  16 not cause conflicts.
  17 +
  18 * A feature will be considered relevant if any of the following are true
  19 +
  20 ** It is referenced by `toolset.flags` or `toolset.uses-features`
  21 ** It is used by the requirements of a generator
  22 ** It is a sub-feature of a relevant feature
  23 ** It has a sub-feature which is relevant
  24 ** It is a composite feature, and any composed feature is relevant
  25 ** It affects target alternative selection for a main target
  26 ** It is a propagated feature and is relevant for any dependency
  27 ** It is relevant for any dependency created by the same main target
  28 ** It is used in the condition of a conditional property and the corresponding
  29   value is relevant
  30 ** It is explicitly named as relevant
  31 +
  32 * Relevant features cannot be automatically deduced in the following cases:
  33 +
  34 ** Indirect conditionals. Solution: return properties of the form
  35 `<relevant>result-feature:<relevant>condition-feature`
  36 +
  37 NOTE: This isn't really a conditional, although for most purposes it functions
  38 like one. In particular, it does not support multiple comma-separated elements
  39 in the condition, and it does work correctly even in contexts where conditional
  40 properties are not allowed
  41 ** Action rules that read properties. Solution: add toolset.uses-features to
  42   tell B2 that the feature is actually used.
  43 ** Generators and targets that manipulate property-sets directly. Solution:
  44   set <relevant> manually.
  45
  46 |# # end::doc[]
  47
  48 feature.feature relevant : : incidental free ;