eclass/java-utils-2: Sync with Gentoo

It's from Gentoo commit cb202546d81ed4e591c366d192e7b15d4c184ffa.

sdk_container/src/third_party/portage-stable/eclass/java-utils-2.eclass

@@ -218,6 +218,46 @@ JAVA_PKG_COMPILERS_CONF=${JAVA_PKG_COMPILERS_CONF:="/etc/java-config-2/build/com
 # 	ebuild foo.ebuild compile
 # @CODE
 
+# @ECLASS_VARIABLE: JAVADOC_CLASSPATH
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Comma or space separated list of java packages that are needed for generating
+# javadocs. Can be used to avoid overloading the compile classpath in multi-jar
+# packages if there are jar files which have different dependencies.
+#
+# @CODE
+# Example:
+# 	JAVADOC_CLASSPATH="
+# 		jna-4
+# 		jsch
+# 	"
+# @CODE
+
+# @ECLASS_VARIABLE: JAVADOC_SRC_DIRS
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# An array of directories relative to ${S} which contain the sources of
+# the application. It needs to sit in global scope; if put in src_compile()
+# it would not work.
+# It is needed by the java-pkg-simple.eclass to decide whether to call ejavadoc
+# or not. If this variable is defined then java-pkg-simple_src_compile will not
+# call ejavadoc automatically. ejavadoc has then to be called explicitly from
+# the ebuild. It is meant for usage in multi-jar packages in order to avoid an
+# extra compilation run only for producing the javadocs.
+#
+# @CODE
+# Example:
+#	JAVADOC_SRC_DIRS=(
+#	    "${PN}-core"
+#	    "${PN}-jsch"
+#	    "${PN}-pageant"
+#	    "${PN}-sshagent"
+#	    "${PN}-usocket-jna"
+#	    "${PN}-usocket-nc"
+#	    "${PN}-connector-factory"
+#	)
+# @CODE
+
 # TODO document me
 JAVA_PKG_QA_VIOLATIONS=0
 
@@ -2152,9 +2192,27 @@ ejavadoc() {
 		einfo "javadoc ${javadoc_args} ${@}"
 	fi
 
+	if [[ "${JAVADOC_SRC_DIRS[@]}" ]]; then
+		mkdir -p target/api || die "cannot create target/api"
+		local dependency
+		for dependency in ${JAVADOC_CLASSPATH}; do
+			classpath="${classpath}:$(java-pkg_getjars \
+				--build-only \
+				--with-dependencies \
+				${dependency})"
+		done
+		find "${JAVADOC_SRC_DIRS[@]}" -name '*.java' > sources
+		javadoc \
+			"${javadoc_args}" \
+			-d target/api \
+			-cp "${classpath}" \
+			-quiet \
+			@sources || die "ejavadoc failed"
+	else
 		local args=( javadoc ${javadoc_args} "${@}" )
 		echo "${args[@]}" >&2
 		"${args[@]}" || die "ejavadoc failed"
+	fi
 }
 
 # @FUNCTION: java-pkg_filter-compiler