Track field names in the adapter lookup stack. (#616)

* Track field names in the adapter lookup stack.

This allows for an error message that includes field names to track down the cause of adapter creation failure for deeply nested structures.

* Use a single stack in Moshi client.

* Make optional fieldName parameter public API.

* Simplify error message.

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

@@ -95,14 +95,15 @@ final class ClassJsonAdapter<T> extends JsonAdapter<T> {
         // Look up a type adapter for this type.
         Type fieldType = resolve(type, rawType, field.getGenericType());
         Set<? extends Annotation> annotations = Util.jsonAnnotations(field);
-        JsonAdapter<Object> adapter = moshi.adapter(fieldType, annotations);
+        String fieldName = field.getName();
+        JsonAdapter<Object> adapter = moshi.adapter(fieldType, annotations, fieldName);
 
         // Create the binding between field and JSON.
         field.setAccessible(true);
 
         // Store it using the field's name. If there was already a field with this name, fail!
         Json jsonAnnotation = field.getAnnotation(Json.class);
-        String name = jsonAnnotation != null ? jsonAnnotation.name() : field.getName();
+        String name = jsonAnnotation != null ? jsonAnnotation.name() : fieldName;
         FieldBinding<Object> fieldBinding = new FieldBinding<>(name, field, adapter);
         FieldBinding<?> replaced = fieldBindings.put(name, fieldBinding);
         if (replaced != null) {

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

@@ -90,8 +90,18 @@ public final class Moshi {
   }
 
   @CheckReturnValue
-  @SuppressWarnings("unchecked") // Factories are required to return only matching JsonAdapters.
   public <T> JsonAdapter<T> adapter(Type type, Set<? extends Annotation> annotations) {
+    return adapter(type, annotations, null);
+  }
+
+  /**
+   * @param fieldName An optional field name associated with this type. The field name is used as a
+   * hint for better adapter lookup error messages for nested structures.
+   */
+  @CheckReturnValue
+  @SuppressWarnings("unchecked") // Factories are required to return only matching JsonAdapters.
+  public <T> JsonAdapter<T> adapter(Type type, Set<? extends Annotation> annotations,
+      @Nullable String fieldName) {
     if (type == null) {
       throw new NullPointerException("type == null");
     }
@@ -123,8 +133,10 @@ public final class Moshi {
     }
 
     // Prepare for re-entrant calls, then ask each factory to create a type adapter.
-    DeferredAdapter<T> deferredAdapter = new DeferredAdapter<>(cacheKey);
+    DeferredAdapter<T> deferredAdapter = new DeferredAdapter<>(type, fieldName, cacheKey);
+
     deferredAdapters.add(deferredAdapter);
+    int lastIndex = deferredAdapters.size() - 1;
     try {
       for (int i = 0, size = factories.size(); i < size; i++) {
         JsonAdapter<T> result = (JsonAdapter<T>) factories.get(i).create(type, annotations, this);
@@ -133,12 +145,19 @@ public final class Moshi {
           synchronized (adapterCache) {
             adapterCache.put(cacheKey, result);
           }
+          // Remove the type or field name only when we succeed in creating the adapter,
+          // so we have the full stack  at the top level.
+          deferredAdapters.remove(lastIndex);
           return result;
         }
       }
+    } catch (IllegalArgumentException e) {
+      if (lastIndex == 0) { // Rewrite the exception at the top level.
+        e = errorWithFields(deferredAdapters, e);
+      }
+      throw e;
     } finally {
-      deferredAdapters.remove(deferredAdapters.size() - 1);
-      if (deferredAdapters.isEmpty()) {
+      if (lastIndex == 0) {
         reentrantCalls.remove();
       }
     }
@@ -181,6 +200,27 @@ public final class Moshi {
     return Arrays.asList(type, annotations);
   }
 
+  static IllegalArgumentException errorWithFields(List<DeferredAdapter<?>> typesAndFieldNames,
+      IllegalArgumentException e) {
+    int size = typesAndFieldNames.size();
+    if (size == 1 && typesAndFieldNames.get(0).fieldName == null) {
+      return e;
+    }
+    StringBuilder errorMessageBuilder = new StringBuilder(e.getMessage());
+    for (int i = size - 1; i >= 0; i--) {
+      DeferredAdapter<?> deferredAdapter = typesAndFieldNames.get(i);
+      errorMessageBuilder
+          .append("\nfor ")
+          .append(deferredAdapter.type);
+      if (deferredAdapter.fieldName != null) {
+        errorMessageBuilder
+            .append(' ')
+            .append(deferredAdapter.fieldName);
+      }
+    }
+    return new IllegalArgumentException(errorMessageBuilder.toString(), e);
+  }
+
   public static final class Builder {
     final List<JsonAdapter.Factory> factories = new ArrayList<>();
 
@@ -250,11 +290,15 @@ public final class Moshi {
    * <p>Typically this is necessary in self-referential object models, such as an {@code Employee}
    * class that has a {@code List<Employee>} field for an organization's management hierarchy.
    */
-  private static class DeferredAdapter<T> extends JsonAdapter<T> {
+  private static final class DeferredAdapter<T> extends JsonAdapter<T> {
+    final Type type;
+    final @Nullable String fieldName;
     @Nullable Object cacheKey;
     private @Nullable JsonAdapter<T> delegate;
 
-    DeferredAdapter(Object cacheKey) {
+    DeferredAdapter(Type type, @Nullable String fieldName, Object cacheKey) {
+      this.type = type;
+      this.fieldName = fieldName;
       this.cacheKey = cacheKey;
     }
 

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

@@ -332,7 +332,12 @@ public final class JsonQualifiersTest {
       moshi.adapter(StringAndFooString.class);
       fail();
     } catch (IllegalArgumentException expected) {
-      assertThat(expected).hasMessage("No @FromJson adapter for class java.lang.String "
+      assertThat(expected).hasMessage("No @FromJson adapter for class java.lang.String annotated "
+          + "[@com.squareup.moshi.JsonQualifiersTest$FooPrefix()]"
+          + "\nfor class java.lang.String b"
+          + "\nfor class com.squareup.moshi.JsonQualifiersTest$StringAndFooString");
+      assertThat(expected).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
+      assertThat(expected.getCause()).hasMessage("No @FromJson adapter for class java.lang.String "
           + "annotated [@com.squareup.moshi.JsonQualifiersTest$FooPrefix()]");
       assertThat(expected).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
       assertThat(expected.getCause()).hasMessage("No next JsonAdapter for class "
@@ -356,7 +361,12 @@ public final class JsonQualifiersTest {
       moshi.adapter(StringAndFooString.class);
       fail();
     } catch (IllegalArgumentException expected) {
-      assertThat(expected).hasMessage("No @ToJson adapter for class java.lang.String "
+      assertThat(expected).hasMessage("No @ToJson adapter for class java.lang.String annotated "
+          + "[@com.squareup.moshi.JsonQualifiersTest$FooPrefix()]"
+          + "\nfor class java.lang.String b"
+          + "\nfor class com.squareup.moshi.JsonQualifiersTest$StringAndFooString");
+      assertThat(expected).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
+      assertThat(expected.getCause()).hasMessage("No @ToJson adapter for class java.lang.String "
           + "annotated [@com.squareup.moshi.JsonQualifiersTest$FooPrefix()]");
       assertThat(expected).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
       assertThat(expected.getCause()).hasMessage("No next JsonAdapter for class "

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

@@ -45,6 +45,7 @@ import static java.lang.annotation.RetentionPolicy.RUNTIME;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
 
+@SuppressWarnings("CheckReturnValue")
 public final class MoshiTest {
   @Test public void booleanAdapter() throws Exception {
     Moshi moshi = new Moshi.Builder().build();
@@ -955,6 +956,74 @@ public final class MoshiTest {
     }
   }
 
+  static final class HasPlatformType {
+    ArrayList<String> strings;
+
+    static final class Wrapper {
+      HasPlatformType hasPlatformType;
+    }
+
+    static final class ListWrapper {
+      List<HasPlatformType> platformTypes;
+    }
+  }
+
+  @Test public void reentrantFieldErrorMessagesTopLevelMap() {
+    Moshi moshi = new Moshi.Builder().build();
+    try {
+      moshi.adapter(Types.newParameterizedType(Map.class, String.class, HasPlatformType.class));
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "Platform java.util.ArrayList<java.lang.String> (with no annotations) requires explicit "
+              + "JsonAdapter to be registered"
+              + "\nfor java.util.ArrayList<java.lang.String> strings"
+              + "\nfor class com.squareup.moshi.MoshiTest$HasPlatformType"
+              + "\nfor java.util.Map<java.lang.String, "
+              + "com.squareup.moshi.MoshiTest$HasPlatformType>");
+      assertThat(e).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
+      assertThat(e.getCause()).hasMessage("Platform java.util.ArrayList<java.lang.String> "
+          + "(with no annotations) requires explicit JsonAdapter to be registered");
+    }
+  }
+
+  @Test public void reentrantFieldErrorMessagesWrapper() {
+    Moshi moshi = new Moshi.Builder().build();
+    try {
+      moshi.adapter(HasPlatformType.Wrapper.class);
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "Platform java.util.ArrayList<java.lang.String> (with no annotations) requires explicit "
+              + "JsonAdapter to be registered"
+              + "\nfor java.util.ArrayList<java.lang.String> strings"
+              + "\nfor class com.squareup.moshi.MoshiTest$HasPlatformType hasPlatformType"
+              + "\nfor class com.squareup.moshi.MoshiTest$HasPlatformType$Wrapper");
+      assertThat(e).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
+      assertThat(e.getCause()).hasMessage("Platform java.util.ArrayList<java.lang.String> "
+          + "(with no annotations) requires explicit JsonAdapter to be registered");
+    }
+  }
+
+  @Test public void reentrantFieldErrorMessagesListWrapper() {
+    Moshi moshi = new Moshi.Builder().build();
+    try {
+      moshi.adapter(HasPlatformType.ListWrapper.class);
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "Platform java.util.ArrayList<java.lang.String> (with no annotations) requires explicit "
+              + "JsonAdapter to be registered"
+              + "\nfor java.util.ArrayList<java.lang.String> strings"
+              + "\nfor class com.squareup.moshi.MoshiTest$HasPlatformType"
+              + "\nfor java.util.List<com.squareup.moshi.MoshiTest$HasPlatformType> platformTypes"
+              + "\nfor class com.squareup.moshi.MoshiTest$HasPlatformType$ListWrapper");
+      assertThat(e).hasCauseExactlyInstanceOf(IllegalArgumentException.class);
+      assertThat(e.getCause()).hasMessage("Platform java.util.ArrayList<java.lang.String> "
+          + "(with no annotations) requires explicit JsonAdapter to be registered");
+    }
+  }
+
   @Test public void qualifierWithElementsMayNotBeDirectlyRegistered() throws IOException {
     try {
       new Moshi.Builder()