Interfaces syntax

[hajotka]

This adds are(Not)Interfaces and (not)beInterfaces.

The should().onlyBeAccessed().byClassesThat().are*Interfaces() doesn't make sense in Java 7, only with Java 8 with default methods. I added the relevant tests and tried them with Java 8, however currently they are ignored. See TODOs in ShouldOnlyBeAccessedByClassesThatTest.

Accessing a constant from an interface does not count as an access - is this as intended? Also see ShouldOnlyBeAccessedByClassesThatTest.java.

I hereby agree to the terms of the ArchUnit Contributor License Agreement.
Resolves #28

[codecholeric]

Cool, thanks a lot 😃
I would not add the @Ignored test though, because the rest of the test (limiting the test to classes), is valid and useful right now. I would rather add the test without Java 8 specifics, but add a guard, that if we compile ArchUnit with Java 8 language level, the test will fail with a reminder, that the interface case should be added. Unfortunately something like

if (hasMethod(Collection.class, "stream")) {
    Assert.fail("Please extend the test case for accesses from interfaces " +
        "(which was not possible with Java 7)");
}

doesn't work, because even if we have source 1.7, we sometimes want to compile it with JDK 8, and then the test fails, even though it's not possible to use the language features. So maybe adding a TODO plus a guard in build.gradle

if (sourceCompatibility != JavaVersion.VERSION_1_7) {
    throw new IllegalStateException('Please fix TODOs marked with "TODO Java 8"')
}

would work (or do you have a better idea?)
Concerning your question, why the test case with the constant String doesn't work, the compiler inlines primitives and Strings, you can check this by

javap -v someInterface.class

and you'll see, that your String value is actually contained within the class file, thus on bytecode level, there is no access. You can fix this though, by making it an Object, or similar, because those won't be inlined (maybe we don't need the Java 8 guard then, either, because the test can just be written that way?)
Also: Do you think, it would make sense, to add an archunit-example for this added syntax, together with an archunit-integration-test?

[hajotka]

Indeed, when changing the example to access an Object field, the tests work. So no need for a Java 8 guard here.

I'll have a look at adding an integration test.

[codecholeric]

Glad to hear, that it works without any shady workaround 😃
I'll wait for the integration test and then merge the PR (in case you notice some problem while writing the test)

[hajotka]

I've added examples + integration tests, hope they aren't too artificial ;)

There was a problem with the build in archunit-examples, a dependency was missing, running

../gradlew clean build -P example

in archunit-examples failed with a ClassNotFoundException. How about running the examples as a smoke test in the CI?

[codecholeric]

Ah, that dependency I've just removed a little while ago ☹️
Yes, I haven't run -P example, yes it should be tested to compile (even though the tests fail by intention). Still, I don't think I want the dependency on configuration: 'tests' in the long run, since I'm pondering about creating a standalone example project (compare #30)

Anyway, the PR looks good, thank you so much 😃 I'll merge that now...

[codecholeric]

I've added the excludeCategories only where necessary, so I could remove the dependency again...