Expose Java Classpath

[ecmel]

Exposing Java classpath for the current workspace to the Java Script side can be very useful for other extensions. (https://code.visualstudio.com/docs/extensionAPI/vscode-api#_extensions)

[fbricon]

We probably need to expose classpath per scope, i.e. compile vs test for Maven, but also runtime/provided.

For Gradle projects, scope is a more "open" notion, not only are the scopes named differently (compile, compileTest) but it's open to customization. We need a way to extract those informations from Buildship's APIs, ideally. @oehme, @donat any pointers?

[fbricon]

Note: with Java 9's modulepath, we have an extra level of project dependencies

[donat]

@fbricon Actually, we're in the process of adding support separating scopes in the Eclipse runtime classpath. See the related issue and my feature branch. Basically, the idea is that the Gradle eclipse plugin produces extra classpath attributes describing dependency scopes:

Here's an example .classpath file:

<classpath>
    <classpathentry output="bin/main" kind="src" path="src/main/java">
        <attributes>
            <attribute name="gradle_scope" value="main"/>
            <attribute name="gradle_used_by_scope" value="main"/>
        </attributes>
    </classpathentry>
    <classpathentry output="bin/test" kind="src" path="src/test/java">
        <attributes>
            <attribute name="gradle_scope" value="test"/>
            <attribute name="gradle_used_by_scope" value="main,test"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.buildship.core.gradleclasspathcontainer"/>
    <classpathentry path="bin/default" kind="output"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8/"/>
    <classpathentry sourcepath="/Users/donat/.gradle/caches/modules-2/files-2.1/junit/junit/4.12/a6c32b40bf3d76eca54e3c601e5d1470c86fcdfa/junit-4.12-sources.jar" kind="lib" path="/Users/donat/.gradle/caches/modules-2/files-2.1/junit/junit/4.12/2973d150c0dc1fefe998f834810d68f278ea58ec/junit-4.12.jar">
        <attributes>
            <attribute name="gradle_used_by_scope" value="test"/>
        </attributes>
    </classpathentry>
</classpath>

The scope information is based on the source set names (main, test, integTest, etc). By using the scope information, Buildship can figure out which output folders and dependencies should be filtered from the runtime classpath.