Add Muzzle reference creation for interfaces

This will allow muzzle to fail if an implemented interface is missing.

dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/muzzle/Reference.java

@@ -9,10 +9,12 @@
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
+import lombok.ToString;
 import net.bytebuddy.jar.asm.Opcodes;
 import net.bytebuddy.jar.asm.Type;
 
 /** An immutable reference to a jvm class. */
+@ToString
 public class Reference {
   private final Set<Source> sources;
   private final String className;
@@ -129,11 +131,6 @@ private static Set<Flag> mergeFlags(final Set<Flag> flags1, final Set<Flag> flag
     return merged;
   }
 
-  @Override
-  public String toString() {
-    return "Reference<" + className + ">";
-  }
-
   public static class Source {
     private final String name;
     private final int line;

dd-java-agent/agent-tooling/src/main/java/datadog/trace/agent/tooling/muzzle/ReferenceCreator.java

@@ -180,9 +180,16 @@ public void visit(
     refSourceClassName = Utils.getClassName(name);
     refSourceType = Type.getType("L" + name + ";");
     refSourceTypeInternalName = refSourceType.getInternalName();
-    // Additional references we could check
-    // - supertype of class and visible from this package
-    // - interfaces of class and visible from this package
+
+    // Add references to each of the interfaces.
+    for (String iface : interfaces) {
+      addReference(
+          new Reference.Builder(iface)
+              .withSource(refSourceClassName, 0) // We don't have a specific line number to use.
+              .withFlag(Reference.Flag.PUBLIC)
+              .build());
+    }
+    // the super type is handled by the method visitor to the constructor.
     super.visit(version, access, name, signature, superName, interfaces);
   }
 

dd-java-agent/testing/src/test/groovy/muzzle/ReferenceCreatorTest.groovy

@@ -49,6 +49,19 @@ class ReferenceCreatorTest extends AgentTestRunner {
     aFieldRefs.size() == 2
   }
 
+  def "ref test"() {
+    setup:
+    Map<String, Reference> references = ReferenceCreator.createReferencesFrom(MethodBodyAdvice.A.getName(), this.getClass().getClassLoader())
+    def a = references.get('muzzle.TestClasses$MethodBodyAdvice$A')
+    def b = references.get('muzzle.TestClasses$MethodBodyAdvice$B')
+
+    expect:
+    references.keySet() == ['muzzle.TestClasses$MethodBodyAdvice$A', 'muzzle.TestClasses$MethodBodyAdvice$B'].toSet()
+
+    and: "doesn't need to reference self"
+    !(a.getSources().any { it.name == 'muzzle.TestClasses$MethodBodyAdvice$A' })
+  }
+
   def "protected ref test"() {
     setup:
     Map<String, Reference> references = ReferenceCreator.createReferencesFrom(MethodBodyAdvice.B2.getName(), this.getClass().getClassLoader())
@@ -67,6 +80,24 @@ class ReferenceCreatorTest extends AgentTestRunner {
     references.get('muzzle.TestClasses$MethodBodyAdvice$A') != null
   }
 
+  def "interface impl creates references"() {
+    setup:
+    Map<String, Reference> references = ReferenceCreator.createReferencesFrom(MethodBodyAdvice.SomeImplementation.getName(), this.getClass().getClassLoader())
+
+    expect:
+    references.get('muzzle.TestClasses$MethodBodyAdvice$SomeInterface') != null
+    references.size() == 1
+  }
+
+  def "child class creates references"() {
+    setup:
+    Map<String, Reference> references = ReferenceCreator.createReferencesFrom(MethodBodyAdvice.A2.getName(), this.getClass().getClassLoader())
+
+    expect:
+    references.get('muzzle.TestClasses$MethodBodyAdvice$A') != null
+    references.size() == 1
+  }
+
   def "instanceof creates references"() {
     setup:
     Map<String, Reference> references = ReferenceCreator.createReferencesFrom(InstanceofAdvice.getName(), this.getClass().getClassLoader())
@@ -82,7 +113,7 @@ class ReferenceCreatorTest extends AgentTestRunner {
     Map<String, Reference> references = ReferenceCreator.createReferencesFrom(TestClasses.InDyAdvice.getName(), this.getClass().getClassLoader())
 
     expect:
-    references.get('muzzle.TestClasses$MethodBodyAdvice$SomeImplementation') != null
+    references.get('muzzle.TestClasses$MethodBodyAdvice$HasMethod') != null
     references.get('muzzle.TestClasses$MethodBodyAdvice$B') != null
   }
 

dd-java-agent/testing/src/test/java/muzzle/TestClasses.java

@@ -95,10 +95,9 @@ public static boolean instanceofMethod(final Object a) {
 
   // Can't test this until java 7 is dropped.
   public static class InDyAdvice {
-    //    public static MethodBodyAdvice.SomeInterface indyMethod(
-    //        final MethodBodyAdvice.SomeImplementation a) {
+    //    public static MethodBodyAdvice.HasMethod indyMethod(final MethodBodyAdvice.HasMethod a) {
     //      Runnable aStaticMethod = MethodBodyAdvice.B::aStaticMethod;
-    //      return a::someMethod;
+    //      return a::requiredMethod;
     //    }
   }
 }