Introduced tags to reader/writers (#1227)

* Introduced tags to reader/writers

* Removed getTags method

* Added type safety to tag methods

* Changed to explicit class comparison

* Removed ? extends for tags

* Switched to LinkedHashMap

* Allowed polymorphism for tag values

* Simplified tags tests

moshi/src/main/java/com/squareup/moshi/JsonReader.java

@@ -21,6 +21,7 @@ import java.io.Closeable;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import javax.annotation.CheckReturnValue;
@@ -197,6 +198,8 @@ public abstract class JsonReader implements Closeable {
   /** True to throw a {@link JsonDataException} on any attempt to call {@link #skipValue()}. */
   boolean failOnUnknown;
 
+  private Map<Class<?>, Object> tags;
+
   /** Returns a new instance that reads UTF-8 encoded JSON from {@code source}. */
   @CheckReturnValue
   public static JsonReader of(BufferedSource source) {
@@ -569,6 +572,27 @@ public abstract class JsonReader implements Closeable {
     return JsonScope.getPath(stackSize, scopes, pathNames, pathIndices);
   }
 
+  /** Returns the tag value for the given class key. */
+  @SuppressWarnings("unchecked")
+  @CheckReturnValue
+  public final @Nullable <T> T tag(Class<T> clazz) {
+    if (tags == null) {
+      return null;
+    }
+    return (T) tags.get(clazz);
+  }
+
+  /** Assigns the tag value using the given class key and value. */
+  public final <T> void setTag(Class<T> clazz, T value) {
+    if (!clazz.isAssignableFrom(value.getClass())) {
+      throw new IllegalArgumentException("Tag value must be of type " + clazz.getName());
+    }
+    if (tags == null) {
+      tags = new LinkedHashMap<>();
+    }
+    tags.put(clazz, value);
+  }
+
   /**
    * Changes the reader to treat the next name as a string value. This is useful for map adapters so
    * that arbitrary type adapters can use {@link #nextString} to read a name value.

moshi/src/main/java/com/squareup/moshi/JsonWriter.java

@@ -24,6 +24,7 @@ import java.io.Closeable;
 import java.io.Flushable;
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import javax.annotation.CheckReturnValue;
@@ -171,6 +172,8 @@ public abstract class JsonWriter implements Closeable, Flushable {
    */
   int flattenStackSize = -1;
 
+  private Map<Class<?>, Object> tags;
+
   /** Returns a new instance that writes UTF-8 encoded JSON to {@code sink}. */
   @CheckReturnValue
   public static JsonWriter of(BufferedSink sink) {
@@ -561,4 +564,25 @@ public abstract class JsonWriter implements Closeable, Flushable {
   public final String getPath() {
     return JsonScope.getPath(stackSize, scopes, pathNames, pathIndices);
   }
+
+  /** Returns the tag value for the given class key. */
+  @SuppressWarnings("unchecked")
+  @CheckReturnValue
+  public final @Nullable <T> T tag(Class<T> clazz) {
+    if (tags == null) {
+      return null;
+    }
+    return (T) tags.get(clazz);
+  }
+
+  /** Assigns the tag value using the given class key and value. */
+  public final <T> void setTag(Class<T> clazz, T value) {
+    if (!clazz.isAssignableFrom(value.getClass())) {
+      throw new IllegalArgumentException("Tag value must be of type " + clazz.getName());
+    }
+    if (tags == null) {
+      tags = new LinkedHashMap<>();
+    }
+    tags.put(clazz, value);
+  }
 }

moshi/src/test/java/com/squareup/moshi/JsonReaderTest.java

@@ -1433,6 +1433,27 @@ public final class JsonReaderTest {
     assertThat(reader.nextString()).isEqualTo("d");
   }
 
+  @SuppressWarnings("rawtypes")
+  @Test
+  public void tags() throws IOException {
+    JsonReader reader = newReader("{}");
+    assertThat(reader.tag(Integer.class)).isNull();
+    assertThat(reader.tag(CharSequence.class)).isNull();
+
+    reader.setTag(Integer.class, 1);
+    reader.setTag(CharSequence.class, "Foo");
+    try {
+      reader.setTag((Class) CharSequence.class, 1);
+      fail();
+    } catch (IllegalArgumentException expected) {
+      assertThat(expected).hasMessage("Tag value must be of type java.lang.CharSequence");
+    }
+
+    assertThat(reader.tag(Integer.class)).isEqualTo(1).isInstanceOf(Integer.class);
+    assertThat(reader.tag(CharSequence.class)).isEqualTo("Foo").isInstanceOf(String.class);
+    assertThat(reader.tag(String.class)).isNull();
+  }
+
   /** Peek a value, then read it, recursively. */
   private void readValue(JsonReader reader, boolean peekJsonFirst) throws IOException {
     JsonReader.Token token = reader.peek();

moshi/src/test/java/com/squareup/moshi/JsonWriterTest.java

@@ -953,4 +953,25 @@ public final class JsonWriterTest {
     writer.endObject();
     assertThat(factory.json()).isEqualTo("{}");
   }
+
+  @SuppressWarnings("rawtypes")
+  @Test
+  public void tags() throws IOException {
+    JsonWriter writer = factory.newWriter();
+    assertThat(writer.tag(Integer.class)).isNull();
+    assertThat(writer.tag(CharSequence.class)).isNull();
+
+    writer.setTag(Integer.class, 1);
+    writer.setTag(CharSequence.class, "Foo");
+    try {
+      writer.setTag((Class) CharSequence.class, 1);
+      fail();
+    } catch (IllegalArgumentException expected) {
+      assertThat(expected).hasMessage("Tag value must be of type java.lang.CharSequence");
+    }
+
+    assertThat(writer.tag(Integer.class)).isEqualTo(1).isInstanceOf(Integer.class);
+    assertThat(writer.tag(CharSequence.class)).isEqualTo("Foo").isInstanceOf(String.class);
+    assertThat(writer.tag(String.class)).isNull();
+  }
 }