From d27eaa161ad109f81e1e298aa26b3256c433474c Mon Sep 17 00:00:00 2001
From: Eric Cochran <Eric@NightlyNexus.com>
Date: Sat, 28 Jan 2017 20:54:42 -0800
Subject: [PATCH] Add adapter(Type, Class<? extends Annotation>)

---
 .../main/java/com/squareup/moshi/Moshi.java   |  5 +++
 .../main/java/com/squareup/moshi/Types.java   | 37 +++++++++++++++++++
 .../java/com/squareup/moshi/TypesTest.java    | 18 +++++++++
 3 files changed, 60 insertions(+)

diff --git a/moshi/src/main/java/com/squareup/moshi/Moshi.java b/moshi/src/main/java/com/squareup/moshi/Moshi.java
index 39e83f3..16cedad 100644
--- a/moshi/src/main/java/com/squareup/moshi/Moshi.java
+++ b/moshi/src/main/java/com/squareup/moshi/Moshi.java
@@ -61,6 +61,11 @@ public final class Moshi {
     return adapter(type, Util.NO_ANNOTATIONS);
   }
 
+  public <T> JsonAdapter<T> adapter(Type type, Class<? extends Annotation> annotationType) {
+    return adapter(type,
+        Collections.singleton(Types.createJsonQualifierImplementation(annotationType)));
+  }
+
   @SuppressWarnings("unchecked") // Factories are required to return only matching JsonAdapters.
   public <T> JsonAdapter<T> adapter(Type type, Set<? extends Annotation> annotations) {
     type = Types.canonicalize(type);
diff --git a/moshi/src/main/java/com/squareup/moshi/Types.java b/moshi/src/main/java/com/squareup/moshi/Types.java
index 67cac08..02a841f 100644
--- a/moshi/src/main/java/com/squareup/moshi/Types.java
+++ b/moshi/src/main/java/com/squareup/moshi/Types.java
@@ -15,10 +15,14 @@
  */
 package com.squareup.moshi;
 
+import java.lang.annotation.Annotation;
 import java.lang.reflect.Array;
 import java.lang.reflect.GenericArrayType;
 import java.lang.reflect.GenericDeclaration;
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
 import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Proxy;
 import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.lang.reflect.WildcardType;
@@ -137,6 +141,39 @@ public final class Types {
     }
   }
 
+  @SuppressWarnings("unchecked")
+  static <T extends Annotation> T createJsonQualifierImplementation(final Class<T> annotationType) {
+    if (!annotationType.isAnnotation()) {
+      throw new IllegalArgumentException(annotationType + " must be an annotation.");
+    }
+    if (!annotationType.isAnnotationPresent(JsonQualifier.class)) {
+      throw new IllegalArgumentException(annotationType + " must have @JsonQualifier.");
+    }
+    if (annotationType.getDeclaredMethods().length != 0) {
+      throw new IllegalArgumentException(annotationType + " must not declare methods.");
+    }
+    return (T) Proxy.newProxyInstance(annotationType.getClassLoader(),
+        new Class<?>[] { annotationType }, new InvocationHandler() {
+          @Override public Object invoke(Object proxy, Method method, Object[] args)
+              throws Throwable {
+            String methodName = method.getName();
+            switch (methodName) {
+              case "annotationType":
+                return annotationType;
+              case "equals":
+                Object o = args[0];
+                return annotationType.isInstance(o);
+              case "hashCode":
+                return 0;
+              case "toString":
+                return "@" + annotationType.getName() + "()";
+              default:
+                return method.invoke(proxy, args);
+            }
+          }
+        });
+  }
+
   static boolean equal(Object a, Object b) {
     return a == b || (a != null && a.equals(b));
   }
diff --git a/moshi/src/test/java/com/squareup/moshi/TypesTest.java b/moshi/src/test/java/com/squareup/moshi/TypesTest.java
index a41070e..5b91809 100644
--- a/moshi/src/test/java/com/squareup/moshi/TypesTest.java
+++ b/moshi/src/test/java/com/squareup/moshi/TypesTest.java
@@ -15,6 +15,7 @@
  */
 package com.squareup.moshi;
 
+import java.lang.annotation.Retention;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
@@ -23,6 +24,7 @@ import java.util.Map;
 import java.util.Properties;
 import org.junit.Test;
 
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
 
@@ -143,4 +145,20 @@ public final class TypesTest {
     assertThat(Types.mapKeyAndValueTypes(StringIntegerMap.class, StringIntegerMap.class))
         .containsExactly(String.class, Integer.class);
   }
+
+  @Test public void createJsonQualifierImplementation() throws Exception {
+    TestQualifier actual = Types.createJsonQualifierImplementation(TestQualifier.class);
+    TestQualifier expected =
+        (TestQualifier) TypesTest.class.getDeclaredField("unused").getAnnotations()[0];
+    assertThat(actual.annotationType()).isEqualTo(TestQualifier.class);
+    assertThat(actual).isEqualTo(expected);
+    assertThat(actual).isNotEqualTo(null);
+    assertThat(actual.hashCode()).isEqualTo(expected.hashCode());
+    assertThat(actual.getClass()).isNotEqualTo(TestQualifier.class);
+  }
+
+  @TestQualifier private static Object unused;
+
+  @Retention(RUNTIME) @JsonQualifier @interface TestQualifier {
+  }
 }