Move truth-java8-extension classes into the main truth artifact.

While there, make some minor changes to prepare for moving the `Truth8` methods into `Truth`.

This is the first step of #746.

RELNOTES=Moved the `truth-java8-extension` classes into the main `truth` artifact. There is no longer any need to depend on `truth-java8-extension`, which is now empty. (We've also removed the `Truth8` [GWT](https://www.gwtproject.org/) module.)
PiperOrigin-RevId: 597243015

Author: cpovirk

core/src/main/java/com/google/common/truth/IgnoreJRERequirement.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2019 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.common.truth;
+
+import static java.lang.annotation.ElementType.CONSTRUCTOR;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+
+import java.lang.annotation.Target;
+
+/**
+ * Disables Animal Sniffer's checking of compatibility with older versions of Java/Android.
+ */
+@Target({METHOD, CONSTRUCTOR, TYPE})
+@interface IgnoreJRERequirement {}

extensions/java8/src/main/java/com/google/common/truth/IntStreamSubject.java renamed to core/src/main/java/com/google/common/truth/IntStreamSubject.java

@@ -40,12 +40,16 @@
  *
  * @author Kurt Alfred Kluever
  */
-@SuppressWarnings("deprecation") // TODO(b/134064106): design an alternative to no-arg check()
+@SuppressWarnings({
+  "deprecation", // TODO(b/134064106): design an alternative to no-arg check()
+  "Java7ApiChecker", // used only from APIs with Java 8 in their signatures
+})
+@IgnoreJRERequirement
 public final class IntStreamSubject extends Subject {
 
   private final List<?> actualList;
 
-  private IntStreamSubject(FailureMetadata failureMetadata, @Nullable IntStream stream) {
+  IntStreamSubject(FailureMetadata failureMetadata, @Nullable IntStream stream) {
     super(failureMetadata, stream);
     this.actualList =
         (stream == null) ? null : stream.boxed().collect(toCollection(ArrayList::new));

extensions/java8/src/main/java/com/google/common/truth/LongStreamSubject.java renamed to core/src/main/java/com/google/common/truth/LongStreamSubject.java

@@ -40,12 +40,16 @@
  *
  * @author Kurt Alfred Kluever
  */
-@SuppressWarnings("deprecation") // TODO(b/134064106): design an alternative to no-arg check()
+@SuppressWarnings({
+  "deprecation", // TODO(b/134064106): design an alternative to no-arg check()
+  "Java7ApiChecker", // used only from APIs with Java 8 in their signatures
+})
+@IgnoreJRERequirement
 public final class LongStreamSubject extends Subject {
 
   private final List<?> actualList;
 
-  private LongStreamSubject(FailureMetadata failureMetadata, @Nullable LongStream stream) {
+  LongStreamSubject(FailureMetadata failureMetadata, @Nullable LongStream stream) {
     super(failureMetadata, stream);
     this.actualList =
         (stream == null) ? null : stream.boxed().collect(toCollection(ArrayList::new));

extensions/java8/src/main/java/com/google/common/truth/OptionalDoubleSubject.java renamed to core/src/main/java/com/google/common/truth/OptionalDoubleSubject.java

@@ -26,6 +26,8 @@
  *
  * @author Ben Douglass
  */
+@SuppressWarnings("Java7ApiChecker") // used only from APIs with Java 8 in their signatures
+@IgnoreJRERequirement
 public final class OptionalDoubleSubject extends Subject {
 
   private final OptionalDouble actual;

extensions/java8/src/main/java/com/google/common/truth/OptionalIntSubject.java renamed to core/src/main/java/com/google/common/truth/OptionalIntSubject.java

@@ -26,6 +26,8 @@
  *
  * @author Ben Douglass
  */
+@SuppressWarnings("Java7ApiChecker") // used only from APIs with Java 8 in their signatures
+@IgnoreJRERequirement
 public final class OptionalIntSubject extends Subject {
   private final OptionalInt actual;
 

extensions/java8/src/main/java/com/google/common/truth/OptionalLongSubject.java renamed to core/src/main/java/com/google/common/truth/OptionalLongSubject.java

@@ -26,6 +26,8 @@
  *
  * @author Ben Douglass
  */
+@SuppressWarnings("Java7ApiChecker") // used only from APIs with Java 8 in their signatures
+@IgnoreJRERequirement
 public final class OptionalLongSubject extends Subject {
   private final OptionalLong actual;
 

extensions/java8/src/main/java/com/google/common/truth/OptionalSubject.java renamed to core/src/main/java/com/google/common/truth/OptionalSubject.java

@@ -26,6 +26,8 @@
  *
  * @author Christian Gruber
  */
+@SuppressWarnings("Java7ApiChecker") // used only from APIs with Java 8 in their signatures
+@IgnoreJRERequirement
 public final class OptionalSubject extends Subject {
   private final @Nullable Optional<?> actual;
 

extensions/java8/src/main/java/com/google/common/truth/PathSubject.java renamed to core/src/main/java/com/google/common/truth/PathSubject.java

@@ -22,8 +22,9 @@
 /** Assertions for {@link Path} instances. */
 @GwtIncompatible
 @J2ObjCIncompatible
+@J2ktIncompatible
 public final class PathSubject extends Subject {
-  private PathSubject(FailureMetadata failureMetadata, Path actual) {
+  PathSubject(FailureMetadata failureMetadata, Path actual) {
     super(failureMetadata, actual);
   }
 

core/src/main/java/com/google/common/truth/StandardSubjectBuilder.java

@@ -18,7 +18,6 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.annotations.GwtIncompatible;
-import com.google.common.base.Optional;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Multiset;
@@ -149,7 +148,7 @@ public final PrimitiveDoubleArraySubject that(double @Nullable [] actual) {
     return new PrimitiveDoubleArraySubject(metadata(), actual, "array");
   }
 
-  public final GuavaOptionalSubject that(@Nullable Optional<?> actual) {
+  public final GuavaOptionalSubject that(com.google.common.base.@Nullable Optional<?> actual) {
     return new GuavaOptionalSubject(metadata(), actual, "optional");
   }
 

extensions/java8/src/main/java/com/google/common/truth/StreamSubject.java renamed to core/src/main/java/com/google/common/truth/StreamSubject.java

@@ -40,12 +40,16 @@
  *
  * @author Kurt Alfred Kluever
  */
-@SuppressWarnings("deprecation") // TODO(b/134064106): design an alternative to no-arg check()
+@SuppressWarnings({
+  "deprecation", // TODO(b/134064106): design an alternative to no-arg check()
+  "Java7ApiChecker", // used only from APIs with Java 8 in their signatures
+})
+@IgnoreJRERequirement
 public final class StreamSubject extends Subject {
 
   private final List<?> actualList;
 
-  private StreamSubject(FailureMetadata failureMetadata, @Nullable Stream<?> stream) {
+  StreamSubject(FailureMetadata failureMetadata, @Nullable Stream<?> stream) {
     super(failureMetadata, stream);
     this.actualList = (stream == null) ? null : stream.collect(toCollection(ArrayList::new));
   }