Moshi.Builder#setPrettyPrinting + failing test

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

@@ -105,6 +105,10 @@ final class BufferedSinkJsonWriter extends JsonWriter {
     }
   }
 
+  @Override public final String getIndent() {
+    return indent != null ? indent : "";
+  }
+
   @Override public final void setLenient(boolean lenient) {
     this.lenient = lenient;
   }

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

@@ -136,6 +136,35 @@ public abstract class JsonAdapter<T> {
     };
   }
 
+  /**
+   * Return a JSON adapter equal to this, but using {@code indent} to control how the result is
+   * formatted. The {@code indent} string to be repeated for each level of indentation in the
+   * encoded document. If {@code indent.isEmpty()} the encoded document will be compact. Otherwise
+   * the encoded document will be more human-readable.
+   *
+   * @param indent a string containing only whitespace.
+   */
+  public JsonAdapter<T> indent(final String indent) {
+    final JsonAdapter<T> delegate = this;
+    return new JsonAdapter<T>() {
+      @Override public T fromJson(JsonReader reader) throws IOException {
+        return delegate.fromJson(reader);
+      }
+      @Override public void toJson(JsonWriter writer, T value) throws IOException {
+        String originalIndent = writer.getIndent();
+        writer.setIndent(indent);
+        try {
+          delegate.toJson(writer, value);
+        } finally {
+          writer.setIndent(originalIndent);
+        }
+      }
+      @Override public String toString() {
+        return delegate + ".indent(\"" + indent + "\")";
+      }
+    };
+  }
+
   public interface Factory {
     /**
      * Attempts to create an adapter for {@code type} annotated with {@code annotations}. This

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

@@ -68,7 +68,7 @@ import okio.BufferedSink;
  * This code encodes the above structure: <pre>   {@code
  *   public void writeJsonStream(BufferedSink sink, List<Message> messages) throws IOException {
  *     JsonWriter writer = JsonWriter.of(sink);
- *     writer.setIndentSpaces(4);
+ *     writer.setIndent("  ");
  *     writeMessagesArray(writer, messages);
  *     writer.close();
  *   }
@@ -137,6 +137,12 @@ public abstract class JsonWriter implements Closeable, Flushable {
    */
   public abstract void setIndent(String indent);
 
+  /**
+   * Returns a string containing only whitespace, used for each level of
+   * indentation. If empty, the encoded document will be compact.
+   */
+  public abstract String getIndent();
+
   /**
    * Configure this writer to relax its syntax rules. By default, this writer
    * only emits well-formed JSON as specified by <a

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

@@ -33,7 +33,7 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import javax.crypto.KeyGenerator;
-import org.junit.Assert;
+import okio.Buffer;
 import org.junit.Test;
 
 import static com.squareup.moshi.TestUtil.newReader;
@@ -546,6 +546,42 @@ public final class MoshiTest {
         .isEqualTo(new Pizza(18, true));
   }
 
+  @Test public void indent() throws Exception {
+    Moshi moshi = new Moshi.Builder().add(Pizza.class, new PizzaAdapter()).build();
+    JsonAdapter<Pizza> jsonAdapter = moshi.adapter(Pizza.class);
+
+    Pizza pizza = new Pizza(15, true);
+    assertThat(jsonAdapter.indent("  ").toJson(pizza)).isEqualTo(""
+        + "{\n"
+        + "  \"size\": 15,\n"
+        + "  \"extra cheese\": true\n"
+        + "}");
+  }
+
+  @Test public void unindent() throws Exception {
+    Moshi moshi = new Moshi.Builder().add(Pizza.class, new PizzaAdapter()).build();
+    JsonAdapter<Pizza> jsonAdapter = moshi.adapter(Pizza.class);
+
+    Buffer buffer = new Buffer();
+    JsonWriter writer = JsonWriter.of(buffer);
+    writer.setLenient(true);
+    writer.setIndent("  ");
+
+    Pizza pizza = new Pizza(15, true);
+
+    // Calling JsonAdapter.indent("") can remove indentation.
+    jsonAdapter.indent("").toJson(writer, pizza);
+    assertThat(buffer.readUtf8()).isEqualTo("{\"size\":15,\"extra cheese\":true}");
+
+    // Indentation changes only apply to their use.
+    jsonAdapter.toJson(writer, pizza);
+    assertThat(buffer.readUtf8()).isEqualTo(""
+        + "{\n"
+        + "  \"size\": 15,\n"
+        + "  \"extra cheese\": true\n"
+        + "}");
+  }
+
   @Test public void composingJsonAdapterFactory() throws Exception {
     Moshi moshi = new Moshi.Builder()
         .add(new MealDealAdapterFactory())