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Add "relevance" feature docs from develop.

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Rene Rivera
2018-01-21 20:44:33 -06:00
parent bb35c3f9c0
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doc/src/reference.adoc
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@@ -485,6 +485,41 @@ shared libraries. This feature corresponds to the IDE option found in the
project settings dialog, under Configuration Properties -> Manifest
Tool -> Input and Output -> Additional Manifest Files.
`relevant`::
*Allowed values:* the name of any feature.
+
This feature is used to indicate which other features are relevant for a
given target. It is usually not necessary to manage it explicitly, as
Boost.Build can deduce it in most cases. Features which are not relevant
will not affect target paths, and will not cause conflicts.
+
* A feature will be considered relevant if any of the following are true
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** It is referenced by `toolset.flags` or `toolset.uses-features`
** It is used by the requirements of a generator
** It is a subfeature of a relevant feature
** It has a subfeature which is relevant
** It is a composite feature, and any composed feature is relevant
** It affects target alternative selection for a main target
** It is a propagated feature and is relevant for any dependency
** It is relevant for any dependency created by the same main target
** It is used in the condition of a conditional property and the corresponding
value is relevant
** It is explicitly named as relevent
+
* Relevant features cannot be automatically deduced in the following cases:
+
** Indirect conditionals. Solution: return properties of the form
`<relevant>result-feature:<relevant>condition-feature`
+
NOTE: This isn't really a conditional, although for most purposes it
functions like one. In particular, it does not support multiple
comma-separated elements in the condition, and it does work correctly even
in contexts where conditional properties are not allowed
** Action rules that read properties. Solution: add toolset.uses-features to
tell Boost.Build that the feature is actually used.
** Generators and targets that manipulate property-sets directly. Solution: set <relevant> manually.
[[bbv2.reference.tools]]
== Builtin tools