Add specification for extracted source dependencies.

Add specs2 specification (unit test) which documents current dependency
extraction logic's behavior. It exercises `direct` and `publicInherited`
relations.

This test is akin to `source-dependencies/inherited-dependencies` scripted
test. We keep both because this test will diverge in next commit to test
`memberRef` and `inheritance` relations.

The idea behind adding this test and then modifying the
`memberRefAndInheritanceDeps` flag so we test `memberRef` and `inheritance`
is that we can show precisely the differences between those two dependency
tracking mechanisms.

compile/interface/src/test/scala/xsbt/DependencySpecification.scala

@@ -0,0 +1,82 @@
+package xsbt
+
+import org.junit.runner.RunWith
+import xsbti.api.ClassLike
+import xsbti.api.Def
+import xsbt.api.SameAPI
+import org.specs2.mutable.Specification
+import org.specs2.runner.JUnitRunner
+
+import ScalaCompilerForUnitTesting.ExtractedSourceDependencies
+
+@RunWith(classOf[JUnitRunner])
+class DependencySpecification extends Specification {
+
+	"Extracted source dependencies from public members" in {
+		val sourceDependencies = extractSourceDependenciesPublic
+		val memberRef = sourceDependencies.memberRef
+		val inheritance = sourceDependencies.inheritance
+		memberRef('A) === Set.empty
+		inheritance('A) === Set.empty
+		memberRef('B) === Set('A, 'D)
+		inheritance('B) === Set('D)
+		memberRef('C) === Set('A)
+		inheritance('C) === Set.empty
+		memberRef('D) === Set.empty
+		inheritance('D) === Set.empty
+		memberRef('E) === Set.empty
+		inheritance('E) === Set.empty
+		memberRef('F) === Set('A, 'B, 'C, 'D, 'E)
+		inheritance('F) === Set('A, 'C, 'E)
+		memberRef('H) === Set('G, 'E)
+		// aliases and applied type constructors are expanded so we have inheritance dependency on B
+		inheritance('H) === Set('D, 'E, 'B)
+	}
+
+	"Extracted source dependencies from private members" in {
+		val sourceDependencies = extractSourceDependenciesPrivate
+		val memberRef = sourceDependencies.memberRef
+		val inheritance = sourceDependencies.inheritance
+		memberRef('A) === Set.empty
+		inheritance('A) === Set.empty
+		memberRef('B) === Set.empty
+		inheritance('B) === Set.empty
+		memberRef('C) === Set('A)
+		inheritance('C) === Set.empty
+		memberRef('D) === Set('B)
+		inheritance('D) === Set.empty
+	}
+
+	private def extractSourceDependenciesPublic: ExtractedSourceDependencies = {
+		val srcA = "class A"
+		val srcB = "class B extends D[A]"
+		val srcC = """|class C {
+		  |  def a: A = null
+		  |}""".stripMargin
+		val srcD = "class D[T]"
+		val srcE = "trait E[T]"
+		val srcF = "trait F extends A with E[D[B]] { self: C => }"
+		val srcG = "object G { type T[x] = B }"
+		// T is a type constructor [x]B
+		// B extends D
+		// E verifies the core type gets pulled out
+		val srcH = "trait H extends G.T[Int] with (E[Int] @unchecked)"
+
+		val compilerForTesting = new ScalaCompilerForUnitTesting(memberRefAndInheritanceDeps = false)
+		val sourceDependencies = compilerForTesting.extractDependenciesFromSrcs('A -> srcA, 'B -> srcB, 'C -> srcC,
+			'D -> srcD, 'E -> srcE, 'F -> srcF, 'G -> srcG, 'H -> srcH)
+		sourceDependencies
+	}
+
+	private def extractSourceDependenciesPrivate: ExtractedSourceDependencies = {
+		val srcA = "class A"
+		val srcB = "class B"
+		val srcC = "class C { private class Inner1 extends A }"
+		val srcD = "class D { def foo: Unit = { class Inner2 extends B } }"
+
+		val compilerForTesting = new ScalaCompilerForUnitTesting(memberRefAndInheritanceDeps = false)
+		val sourceDependencies =
+			compilerForTesting.extractDependenciesFromSrcs('A -> srcA, 'B -> srcB, 'C -> srcC, 'D -> srcD)
+		sourceDependencies
+	}
+}