Add @CheckReturnValue to our packages.

...as threatened in
#2676 (comment).

Author: cpovirk

extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java

@@ -31,7 +31,8 @@ public class PostConstructAdapterFactoryTest {
   public void test() throws Exception {
     Gson gson =
         new GsonBuilder().registerTypeAdapterFactory(new PostConstructAdapterFactory()).create();
-    gson.fromJson("{\"bread\": \"white\", \"cheese\": \"cheddar\"}", Sandwich.class);
+    Sandwich unused =
+        gson.fromJson("{\"bread\": \"white\", \"cheese\": \"cheddar\"}", Sandwich.class);
     try {
       gson.fromJson("{\"bread\": \"cheesey bread\", \"cheese\": \"swiss\"}", Sandwich.class);
       fail();

gson/src/main/java/com/google/gson/annotations/package-info.java

@@ -19,4 +19,5 @@
  *
  * @author Inderjeet Singh, Joel Leitch
  */
+@com.google.errorprone.annotations.CheckReturnValue
 package com.google.gson.annotations;

gson/src/main/java/com/google/gson/internal/package-info.java

@@ -20,4 +20,5 @@
  *
  * @author Inderjeet Singh, Joel Leitch, Jesse Wilson
  */
+@com.google.errorprone.annotations.CheckReturnValue
 package com.google.gson.internal;

gson/src/main/java/com/google/gson/package-info.java

@@ -24,4 +24,5 @@
  *
  * @author Inderjeet Singh, Joel Leitch
  */
+@com.google.errorprone.annotations.CheckReturnValue
 package com.google.gson;

gson/src/main/java/com/google/gson/reflect/package-info.java

@@ -19,4 +19,5 @@
  *
  * @author Inderjeet Singh, Joel Leitch
  */
+@com.google.errorprone.annotations.CheckReturnValue
 package com.google.gson.reflect;

gson/src/main/java/com/google/gson/stream/package-info.java

@@ -15,4 +15,5 @@
  */
 
 /** This package provides classes for processing JSON in an efficient streaming way. */
+@com.google.errorprone.annotations.CheckReturnValue
 package com.google.gson.stream;

gson/src/test/java/com/google/gson/functional/DelegateTypeAdapterTest.java

@@ -54,7 +54,8 @@ public void testDelegateInvoked() {
       bags.add(new BagOfPrimitives(i, i, i % 2 == 0, String.valueOf(i)));
     }
     String json = gson.toJson(bags);
-    gson.fromJson(json, new TypeToken<List<BagOfPrimitives>>() {}.getType());
+    List<BagOfPrimitives> unused =
+        gson.fromJson(json, new TypeToken<List<BagOfPrimitives>>() {}.getType());
     // 11: 1 list object, and 10 entries. stats invoked on all 5 fields
     assertThat(stats.numReads).isEqualTo(51);
     assertThat(stats.numWrites).isEqualTo(51);
@@ -64,7 +65,7 @@ public void testDelegateInvoked() {
   public void testDelegateInvokedOnStrings() {
     String[] bags = {"1", "2", "3", "4"};
     String json = gson.toJson(bags);
-    gson.fromJson(json, String[].class);
+    String[] unused = gson.fromJson(json, String[].class);
     // 1 array object with 4 elements.
     assertThat(stats.numReads).isEqualTo(5);
     assertThat(stats.numWrites).isEqualTo(5);

gson/src/test/java/com/google/gson/functional/JsonAdapterAnnotationOnClassesTest.java

@@ -251,7 +251,7 @@ public void write(JsonWriter out, A value) throws IOException {
 
       @Override
       public A read(JsonReader in) throws IOException {
-        in.nextString();
+        String unused = in.nextString();
         return new A("jsonAdapter");
       }
     }
@@ -277,7 +277,7 @@ public void write(JsonWriter out, T value) throws IOException {
           @SuppressWarnings("unchecked")
           @Override
           public T read(JsonReader in) throws IOException {
-            in.nextString();
+            String unused = in.nextString();
             return (T) new C("jsonAdapterFactory");
           }
         };
@@ -329,7 +329,7 @@ public void write(JsonWriter out, User user) throws IOException {
     public User read(JsonReader in) throws IOException {
       // implement read: split name into firstName and lastName
       in.beginObject();
-      in.nextName();
+      String unused = in.nextName();
       List<String> nameParts = Splitter.on(" ").splitToList(in.nextString());
       in.endObject();
       return new User(nameParts.get(0), nameParts.get(1));
@@ -348,7 +348,7 @@ public void write(JsonWriter out, NullableClass value) throws IOException {
 
     @Override
     public NullableClass read(JsonReader in) throws IOException {
-      in.nextString();
+      String unused = in.nextString();
       return new NullableClass();
     }
   }

gson/src/test/java/com/google/gson/functional/ReflectionAccessTest.java

@@ -118,7 +118,7 @@ public Object read(JsonReader in) throws IOException {
   private static JsonIOException assertInaccessibleException(String json, Class<?> toDeserialize) {
     Gson gson = new Gson();
     try {
-      gson.fromJson(json, toDeserialize);
+      Object unused = gson.fromJson(json, toDeserialize);
       throw new AssertionError(
           "Missing exception; test has to be run with `--illegal-access=deny`");
     } catch (JsonSyntaxException e) {

gson/src/test/java/com/google/gson/reflect/TypeTokenTest.java

@@ -328,7 +328,7 @@ class SubSubTypeToken2 extends SubTypeToken<Integer> {}
   }
 
   private static <M> void createTypeTokenTypeVariable() {
-    new TypeToken<M>() {};
+    TypeToken<M> unused = new TypeToken<M>() {};
   }
 
   /**

metrics/src/main/java/com/google/gson/metrics/BagOfPrimitivesDeserializationBenchmark.java

@@ -48,7 +48,7 @@ void setUp() throws Exception {
   /** Benchmark to measure Gson performance for deserializing an object */
   public void timeBagOfPrimitivesDefault(int reps) {
     for (int i = 0; i < reps; ++i) {
-      gson.fromJson(json, BagOfPrimitives.class);
+      BagOfPrimitives unused = gson.fromJson(json, BagOfPrimitives.class);
     }
   }
 

metrics/src/main/java/com/google/gson/metrics/CollectionsDeserializationBenchmark.java

@@ -56,7 +56,7 @@ void setUp() throws Exception {
   /** Benchmark to measure Gson performance for deserializing an object */
   public void timeCollectionsDefault(int reps) {
     for (int i = 0; i < reps; ++i) {
-      gson.fromJson(json, LIST_TYPE_TOKEN);
+      List<BagOfPrimitives> unused = gson.fromJson(json, LIST_TYPE_TOKEN);
     }
   }
 

metrics/src/main/java/com/google/gson/metrics/ParseBenchmark.java

@@ -29,6 +29,7 @@
 import com.google.caliper.Param;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
 import com.google.gson.JsonParser;
 import com.google.gson.annotations.SerializedName;
 import com.google.gson.reflect.TypeToken;
@@ -195,19 +196,19 @@ private static void readToken(JsonReader reader) throws IOException {
             reader.endObject();
             break;
           case NAME:
-            reader.nextName();
+            String unusedName = reader.nextName();
             break;
           case BOOLEAN:
-            reader.nextBoolean();
+            boolean unusedBoolean = reader.nextBoolean();
             break;
           case NULL:
             reader.nextNull();
             break;
           case NUMBER:
-            reader.nextLong();
+            long unusedLong = reader.nextLong();
             break;
           case STRING:
-            reader.nextString();
+            String unusedString = reader.nextString();
             break;
           case END_DOCUMENT:
             return;
@@ -274,7 +275,7 @@ public void parse(char[] data, Document document) throws Exception {
   private static class GsonDomParser implements Parser {
     @Override
     public void parse(char[] data, Document document) throws Exception {
-      JsonParser.parseReader(new CharArrayReader(data));
+      JsonElement unused = JsonParser.parseReader(new CharArrayReader(data));
     }
   }
 
@@ -284,7 +285,7 @@ private static class GsonBindParser implements Parser {
 
     @Override
     public void parse(char[] data, Document document) throws Exception {
-      gson.fromJson(new CharArrayReader(data), document.gsonType);
+      Object unused = gson.fromJson(new CharArrayReader(data), document.gsonType);
     }
   }
 

metrics/src/main/java/com/google/gson/metrics/SerializationBenchmark.java

@@ -45,7 +45,7 @@ void setUp() throws Exception {
 
   public void timeObjectSerialization(int reps) {
     for (int i = 0; i < reps; ++i) {
-      gson.toJson(bag);
+      String unused = gson.toJson(bag);
     }
   }
 }