The methods returned by `BuilderContext.buildMethod()` and `.toBuilderMethods()` can be inherited.

This change addresses cases like this:

```java
interface Parent<BuilderT> {
  BuilderT toBuilder();
  interface Builder<BuilderT, BuiltT> {",
    BuilderT setThing(String x);",
    BuiltT build();",
  }
}

@AutoValue abstract class Foo implements Parent<Foo.Builder> {
  @AutoValue.Builder
  abstract static class Builder implements Parent.Builder<Builder, Foo> {}
}
```

Previously, there would be two problems with this. First, inheriting `toBuilder()` like this didn't work at all, because its return type is `BuilderT` and not `Foo.Builder`. Now we correctly interpret the inherited return type in the context of `Foo`. Second, in `BuilderContext.buildMethod()` we were looking for methods returning `Foo`, and again this failed because the inherited `build()` method returns `BuiltT`. The fix in both cases is to use `Types.asMemberOf` to determine the correct return type in context.

Fixes https://github.com/google/auto/issues/933.

RELNOTES=The methods returned by `BuilderContext.buildMethod()` and `.toBuilderMethods()` can be inherited.
PiperOrigin-RevId: 342670816

4 files changed, 133 insertions, 10 deletions

diff --git a/value/src/it/functional/src/test/java/com/google/auto/value/AutoValueTest.java b/value/src/it/functional/src/test/java/com/google/auto/value/AutoValueTest.java
index 346bc53a..88e2233c 100644
--- a/value/src/it/functional/src/test/java/com/google/auto/value/AutoValueTest.java
+++ b/value/src/it/functional/src/test/java/com/google/auto/value/AutoValueTest.java
@@ -1874,6 +1874,37 @@ public class AutoValueTest {
     assertEquals((Integer) 17, instance3.u());
   }
 
+  public interface ToBuilder<BuilderT> {
+    BuilderT toBuilder();
+  }
+
+  @AutoValue
+  public abstract static class InheritedToBuilder<T, U>
+      implements ToBuilder<InheritedToBuilder.Builder<T, U>> {
+
+    public abstract T t();
+    public abstract U u();
+
+    public static <T, U> Builder<T, U> builder() {
+      return new AutoValue_AutoValueTest_InheritedToBuilder.Builder<T, U>();
+    }
+
+    @AutoValue.Builder
+    public abstract static class Builder<T, U> {
+      public abstract Builder<T, U> setT(T t);
+      public abstract Builder<T, U> setU(U u);
+      public abstract InheritedToBuilder<T, U> build();
+    }
+  }
+
+  @Test
+  public void testInheritedToBuilder() {
+    InheritedToBuilder<Integer, String> x =
+        InheritedToBuilder.<Integer, String>builder().setT(17).setU("wibble").build();
+    InheritedToBuilder<Integer, String> y = x.toBuilder().setT(23).build();
+    assertThat(y.u()).isEqualTo("wibble");
+  }
+
   @AutoValue
   public abstract static class BuilderWithSet<T extends Comparable<T>> {
     public abstract List<T> list();
diff --git a/value/src/main/java/com/google/auto/value/processor/AutoValueProcessor.java b/value/src/main/java/com/google/auto/value/processor/AutoValueProcessor.java
index 51387b2c..326b22a7 100644
--- a/value/src/main/java/com/google/auto/value/processor/AutoValueProcessor.java
+++ b/value/src/main/java/com/google/auto/value/processor/AutoValueProcessor.java
@@ -19,6 +19,7 @@ import static com.google.auto.common.MoreElements.getLocalAndInheritedMethods;
 import static com.google.auto.value.processor.ClassNames.AUTO_VALUE_NAME;
 import static com.google.common.collect.Sets.difference;
 import static com.google.common.collect.Sets.intersection;
+import static java.util.Comparator.naturalOrder;
 import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toList;
 
@@ -36,7 +37,6 @@ import com.google.common.collect.Iterables;
 import java.lang.annotation.Annotation;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.Comparator;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
@@ -136,7 +136,7 @@ public class AutoValueProcessor extends AutoValueOrOneOfProcessor {
     AutoValueExtension.IncrementalExtensionType incrementalType =
         extensions.stream()
             .map(e -> e.incrementalType(processingEnv))
-            .min(Comparator.naturalOrder())
+            .min(naturalOrder())
             .orElse(AutoValueExtension.IncrementalExtensionType.ISOLATING);
     builder.add(OMIT_IDENTIFIERS_OPTION).addAll(optionsFor(incrementalType));
     for (AutoValueExtension extension : extensions) {
@@ -207,7 +207,7 @@ public class AutoValueProcessor extends AutoValueOrOneOfProcessor {
     Optional<BuilderSpec.Builder> builder = builderSpec.getBuilder();
     ImmutableSet<ExecutableElement> toBuilderMethods;
     if (builder.isPresent()) {
-      toBuilderMethods = builder.get().toBuilderMethods(typeUtils(), abstractMethods);
+      toBuilderMethods = builder.get().toBuilderMethods(typeUtils(), type, abstractMethods);
     } else {
       toBuilderMethods = ImmutableSet.of();
     }
diff --git a/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java b/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
index 7e5b17c9..34095202 100644
--- a/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
+++ b/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
@@ -25,6 +25,7 @@ import static java.util.stream.Collectors.toSet;
 import static javax.lang.model.util.ElementFilter.methodsIn;
 import static javax.lang.model.util.ElementFilter.typesIn;
 
+import com.google.auto.common.MoreElements;
 import com.google.auto.common.MoreTypes;
 import com.google.auto.value.extension.AutoValueExtension;
 import com.google.auto.value.processor.AutoValueOrOneOfProcessor.Property;
@@ -49,6 +50,7 @@ import javax.lang.model.element.TypeElement;
 import javax.lang.model.element.TypeParameterElement;
 import javax.lang.model.element.VariableElement;
 import javax.lang.model.type.DeclaredType;
+import javax.lang.model.type.ExecutableType;
 import javax.lang.model.type.TypeKind;
 import javax.lang.model.type.TypeMirror;
 import javax.lang.model.util.Types;
@@ -142,14 +144,23 @@ class BuilderSpec {
 
     @Override
     public Optional<ExecutableElement> buildMethod() {
-      return methodsIn(builderTypeElement.getEnclosedElements()).stream()
+      Types typeUtils = processingEnv.getTypeUtils();
+      DeclaredType builderTypeMirror = MoreTypes.asDeclared(builderTypeElement.asType());
+      return MoreElements.getLocalAndInheritedMethods(
+              builderTypeElement, typeUtils, processingEnv.getElementUtils())
+          .stream()
           .filter(
               m ->
                   m.getSimpleName().contentEquals("build")
                       && !m.getModifiers().contains(Modifier.PRIVATE)
                       && !m.getModifiers().contains(Modifier.STATIC)
-                      && m.getParameters().isEmpty()
-                      && erasedTypeIs(m.getReturnType(), autoValueClass))
+                      && m.getParameters().isEmpty())
+          .filter(
+              m -> {
+                ExecutableType methodMirror =
+                    MoreTypes.asExecutable(typeUtils.asMemberOf(builderTypeMirror, m));
+                return erasedTypeIs(methodMirror.getReturnType(), autoValueClass);
+              })
           .findFirst();
     }
 
@@ -201,18 +212,27 @@ class BuilderSpec {
      * <p>We currently impose that there cannot be more than one such method.
      */
     ImmutableSet<ExecutableElement> toBuilderMethods(
-        Types typeUtils, Set<ExecutableElement> abstractMethods) {
+        Types typeUtils,
+        TypeElement autoValueType,
+        Set<ExecutableElement> abstractMethods) {
 
       List<String> builderTypeParamNames =
           builderTypeElement.getTypeParameters().stream()
               .map(e -> e.getSimpleName().toString())
               .collect(toList());
 
+      DeclaredType autoValueTypeMirror = MoreTypes.asDeclared(autoValueType.asType());
       ImmutableSet.Builder<ExecutableElement> methods = ImmutableSet.builder();
       for (ExecutableElement method : abstractMethods) {
-        if (builderTypeElement.equals(typeUtils.asElement(method.getReturnType()))) {
+        if (!method.getParameters().isEmpty()) {
+          continue;
+        }
+        ExecutableType methodMirror =
+            MoreTypes.asExecutable(typeUtils.asMemberOf(autoValueTypeMirror, method));
+        TypeMirror returnTypeMirror = methodMirror.getReturnType();
+        if (builderTypeElement.equals(typeUtils.asElement(returnTypeMirror))) {
           methods.add(method);
-          DeclaredType returnType = MoreTypes.asDeclared(method.getReturnType());
+          DeclaredType returnType = MoreTypes.asDeclared(returnTypeMirror);
           List<String> typeArguments =
               returnType.getTypeArguments().stream()
                   .filter(t -> t.getKind().equals(TypeKind.TYPEVAR))
@@ -452,7 +472,7 @@ class BuilderSpec {
       return nullableAnnotation;
     }
 
-    public String copy(AutoValueProcessor.Property property) {
+    public String copy(Property property) {
       String copy = copier.copy.apply(property.toString());
       if (property.isNullable() && !copier.acceptsNull) {
         copy = String.format("(%s == null ? null : %s)", property, copy);
diff --git a/value/src/test/java/com/google/auto/value/processor/ExtensionTest.java b/value/src/test/java/com/google/auto/value/processor/ExtensionTest.java
index ce9eeed0..8f74d5df 100644
--- a/value/src/test/java/com/google/auto/value/processor/ExtensionTest.java
+++ b/value/src/test/java/com/google/auto/value/processor/ExtensionTest.java
@@ -1075,6 +1075,78 @@ public class ExtensionTest {
   }
 
   @Test
+  public void builderContextWithInheritance() {
+    JavaFileObject parent = JavaFileObjects.forSourceLines(
+        "foo.bar.Parent",
+        "package foo.bar;",
+        "",
+        "interface Parent<BuilderT> {",
+        "  BuilderT toBuilder();",
+        "  interface Builder<T, BuilderT, BuiltT> {",
+        "    BuilderT setThing(T x);",
+        "    BuiltT build();",
+        "  }",
+        "}");
+    JavaFileObject autoValueClass = JavaFileObjects.forSourceLines(
+        "foo.bar.Baz",
+        "package foo.bar;",
+        "",
+        "import com.google.auto.value.AutoValue;",
+        "",
+        "@AutoValue",
+        "abstract class Baz<T> implements Parent<Baz.Builder<T>> {",
+        "  abstract T thing();",
+        "  static <T> Builder<T> builder() {",
+        "    return new AutoValue_Baz.Builder<>();",
+        "  }",
+        "",
+        "  @AutoValue.Builder",
+        "  abstract static class Builder<T> implements Parent.Builder<T, Builder<T>, Baz<T>> {",
+        "  }",
+        "}");
+    ContextChecker checker =
+        context -> {
+          assertThat(context.builder()).isPresent();
+          BuilderContext builderContext = context.builder().get();
+
+          assertThat(builderContext.builderType().getQualifiedName().toString())
+              .isEqualTo("foo.bar.Baz.Builder");
+
+          Set<ExecutableElement> builderMethods = builderContext.builderMethods();
+          assertThat(builderMethods).hasSize(1);
+          ExecutableElement builderMethod = Iterables.getOnlyElement(builderMethods);
+          assertThat(builderMethod.getSimpleName().toString()).isEqualTo("builder");
+
+          Set<ExecutableElement> toBuilderMethods = builderContext.toBuilderMethods();
+          assertThat(toBuilderMethods).hasSize(1);
+          ExecutableElement toBuilderMethod = Iterables.getOnlyElement(toBuilderMethods);
+          assertThat(toBuilderMethod.getSimpleName().toString()).isEqualTo("toBuilder");
+
+          Optional<ExecutableElement> buildMethod = builderContext.buildMethod();
+          assertThat(buildMethod).isPresent();
+          assertThat(buildMethod.get().getSimpleName().toString()).isEqualTo("build");
+          assertThat(buildMethod.get().getParameters()).isEmpty();
+          assertThat(buildMethod.get().getReturnType().toString()).isEqualTo("BuiltT");
+
+          ExecutableElement autoBuildMethod = builderContext.autoBuildMethod();
+          assertThat(autoBuildMethod).isEqualTo(buildMethod.get());
+
+          Map<String, Set<ExecutableElement>> setters = builderContext.setters();
+          assertThat(setters.keySet()).containsExactly("thing");
+          Set<ExecutableElement> thingSetters = setters.get("thing");
+          assertThat(thingSetters).hasSize(1);
+          ExecutableElement thingSetter = Iterables.getOnlyElement(thingSetters);
+          assertThat(thingSetter.getSimpleName().toString()).isEqualTo("setThing");
+        };
+    ContextCheckingExtension extension = new ContextCheckingExtension(checker);
+    Compilation compilation =
+        javac()
+            .withProcessors(new AutoValueProcessor(ImmutableList.of(extension)))
+            .compile(autoValueClass, parent);
+    assertThat(compilation).succeededWithoutWarnings();
+  }
+
+  @Test
   public void oddBuilderContext() {
     JavaFileObject autoValueClass = JavaFileObjects.forSourceLines(
         "foo.bar.Baz",