libraries/runtime: copy runtime module sources locally to help IDEA find them

libraries/tools/runtime/pom.xml

@@ -16,9 +16,33 @@
     <packaging>jar</packaging>
 
     <build>
-        <sourceDirectory>${project.basedir}/../../../runtime/src</sourceDirectory>
+        <sourceDirectory>target/copied-sources</sourceDirectory>
 
         <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-antrun-plugin</artifactId>
+                <version>1.7</version>
+
+                <executions>
+                    <execution>
+                        <id>copy-sources</id>
+                        <phase>process-sources</phase>
+                        <configuration>
+                            <target>
+                                <delete dir="${basedir}/target/copied-sources" failonerror="false" />
+                                <copy todir="${basedir}/target/copied-sources">
+                                    <fileset dir="${basedir}/../../../runtime/src"/>
+                                </copy>
+                            </target>
+                        </configuration>
+                        <goals>
+                            <goal>run</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-source-plugin</artifactId>