Add more rules to simplify dealing with build features

* Introduce the notion of build feature attributes and add rules
  SetBuildFeatureAttribute and BuildFeatureAttribute to set respectively
  get a build feature attribute.
* Add rule ExtractBuildFeatureArchives to download and extract archives
  and set build feature attributes to extracted entries.
* Add rule UseBuildFeatureHeaders as a shorthand for getting a build
  feature attribute and adding it as a system header search directory.

build/jam/HeadersRules

@@ -412,6 +412,20 @@ rule UsePrivateSystemHeaders
 }
 
 
+rule UseBuildFeatureHeaders feature : attribute 
+{
+	# UseBuildFeatureHeaders <feature> : [ <attribute> ] ;
+	# A shorthand for
+	# UseHeaders [ BuildFeatureAttribute <feature> : <attribute> ] : true ;
+	# Moreover the default value for <attribute> is "headers", which usually
+	# allows the rule to be called with the feature name as the only parameter.
+
+	local headers = [ BuildFeatureAttribute $(feature) : $(attribute:E=headers)
+		: path ] ;
+	UseHeaders $(headers) : true ;
+}
+
+
 rule FStandardOSHeaders
 {
 	local osIncludes = add-ons add-ons/file_system add-ons/graphics

build/jam/MiscRules

@@ -590,3 +590,168 @@ rule EnableBuildFeatures features : specification
 		}
 	}
 }
+
+
+rule BuildFeatureObject feature
+{
+	# BuildFeatureObject <feature> ;
+	# Returns a unique object for the given build feature. It is used for
+	# attaching attribute values to it.
+
+	local featureObject = $(HAIKU_BUILD_FEATURE_$(feature:U)) ;
+	if ! $(featureObject) {
+		featureObject = [ NewUniqueTarget ] ;
+		HAIKU_BUILD_FEATURE_$(feature:U) = $(featureObject) ;
+	}
+
+	return $(featureObject) ;
+}
+
+
+rule SetBuildFeatureAttribute feature : attribute : values : package
+{
+	# SetBuildFeatureAttribute <feature> : <attribute> : <values>
+	#	[ : <package> ] ;
+	# Sets attribute <attribute> of a build feature <feature> to value <values>.
+	# If <package> is specified, it names the package the attribute belongs to.
+
+	local featureObject = [ BuildFeatureObject $(feature) ] ;
+	HAIKU_ATTRIBUTE_$(attribute) on $(featureObject) = $(values) ;
+	if $(package) {
+		HAIKU_ATTRIBUTE_$(attribute):package on $(featureObject) = $(package) ;
+	}
+}
+
+
+rule BuildFeatureAttribute feature : attribute : flags
+{
+	# BuildFeatureAttribute <feature> : <attribute> [ : <flags> ] ;
+	# Returns the value of attribute <attribute> of a build feature <feature>.
+	# Flags can be a list of flags which influence the returned value. Currently
+	# only flag "path" is defined, which will convert the attribute value --
+	# which is assumed to be a list of (gristed) targets with a path relative to
+	# the extraction directory of the build feature archive files -- to paths.
+	# A typical example is the "headers" attribute, whose value can be used as
+	# dependency, but which must be converted to a path to be a valid headers
+	# search path.
+
+	local featureObject = [ BuildFeatureObject $(feature) ] ;
+	local values
+		= [ on $(featureObject) return $(HAIKU_ATTRIBUTE_$(attribute)) ] ;
+	if path in $(flags) {
+		# get the attribute's package and the corresponding extraction dir
+		local package
+			= [ BuildFeatureAttribute $(feature) : $(attribute):package ] ;
+		local directory ;
+		if $(package) {
+			directory = [ BuildFeatureAttribute $(feature)
+				: $(package):directory ] ;
+		}
+
+		# translate the values
+		local paths ;
+		local value ;
+		for value in $(values:G=) {
+			paths += [ FDirName $(directory) $(value) ] ;
+		}
+		values = $(paths) ;
+	}
+
+	return $(values) ;
+}
+
+
+rule ExtractBuildFeatureArchives feature : list
+{
+	# ExtractBuildFeatureArchives <feature> : <list> ;
+	# Downloads and extracts one or more archives for build feature <feature>
+	# and sets attributes for the build feature to extracted entries. The syntax
+	# for <list> is:
+	# "file:" <packageName> <url>
+	#    <attribute>: <value> ...
+	#    ...
+	# "file:" <packageName2> <url2>
+	# ...
+	#
+	# <packageName> specifies a short name for the archive (e.g. "base" for the
+	# base package, "devel" for the development package, etc.), <url> the URL
+	# from which to download the file. <attribute> and be any name and <value>
+	# any relative path in the extraction directory.
+	#
+	# The attribute with the name "depends" will be handled specially. Its
+	# <value> specifies the name of a package the current package depends on
+	# (e.g. "devel" typically depends on "base"). If such a dependency is
+	# specified the current package will be extracted to the same directory as
+	# the package it depends on. The "depends" attribute must precede any other
+	# attribute for the package.
+	#
+	# The rule also sets the build feature attribute "<packageName>:directory"
+	# to the extraction directory for each package.
+
+	while $(list) {
+		if $(list[1]) != file: {
+			Exit "ExtractBuildFeatureArchives: Expected \"file: ...\", got:"
+				$(list) ;
+		}
+
+		local package = $(list[2]) ;
+		local url = $(list[3]) ;
+		local fileName = $(url:BS) ;
+		list = $(list[4-]) ;
+
+		local file = [ DownloadFile $(fileName) : $(url) ] ;
+
+		local directory = [ FDirName $(HAIKU_OPTIONAL_BUILD_PACKAGES_DIR)
+			$(fileName:B) ] ;
+		directory = $(directory:G=$(package)) ;
+
+		while $(list) {
+			local attribute = [ Match "(.*):" : $(list[1]) ] ;
+			if ! $(attribute) {
+				Exit "ExtractBuildFeatureArchives: Expected attribute, got:"
+					$(list) ;
+			}
+			if $(attribute) = file {
+				break ;
+			}
+
+			list = $(list[2-]) ;
+
+			local values ;
+
+			while $(list) {
+				switch $(list[1]) {
+					case *: :
+					{
+						break ;
+					}
+					case * :
+					{
+						values += $(list[1]) ;
+						list = $(list[2-]) ;
+					}
+				}
+			}
+
+			if $(attribute) = depends {
+				# Inherit the extraction directory (with a different grist) and
+				# depend on the extraction directory of the base package.
+				local basePackage = $(values[1]) ;
+				local baseDirectory = [ BuildFeatureAttribute $(feature)
+					: $(basePackage):directory ] ;
+				directory = $(baseDirectory:G=$(package)) ;
+				Depends $(directory) : $(directory:G=$(basePackage)) ;
+			} else {
+				SetBuildFeatureAttribute $(feature) : $(attribute)
+					: [ ExtractArchive $(directory)
+						: $(values) : $(file)
+						: extracted-$(feature)-$(package) ] ;
+				SetBuildFeatureAttribute $(feature) : $(attribute):package
+					: $(package) ;
+			}
+		}
+
+		SetBuildFeatureAttribute $(feature) : $(package):directory
+			: $(directory:G=) ;
+	}
+}