Make it possible to write expect.that(optional).isPresent(), `asser…

…tWithMessage(...).that(optional).isPresent()`, etc., including for `Stream` as well as `Optional`.

That is, you no longer need to use `about(optionals())` (or `about(streams())`). (Later, we'll do the same thing for lesser-used APIs like `optionalInts().)

This CL does _not_ make it possible to write `Truth.assertThat(optional).isPresent()`: For that, you still need to use `Truth8`. A future CL will eliminate the need to use `Truth8`.

This continues our work on #746.

RELNOTES=Added `that` overloads to make it possible to write type-specific assertions when using `expect.that(optional)` and `expect.that(stream)`.
PiperOrigin-RevId: 598637400

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

@@ -24,6 +24,8 @@
 import com.google.common.collect.Table;
 import java.math.BigDecimal;
 import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Stream;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -168,6 +170,19 @@ public final TableSubject that(@Nullable Table<?, ?, ?> actual) {
     return new TableSubject(metadata(), actual);
   }
 
+  @SuppressWarnings({
+    "Java7ApiChecker", // no more dangerous that wherever the user got the Optional
+    "NullableOptional", // Truth always accepts nulls, no matter the type
+  })
+  public final OptionalSubject that(@Nullable Optional<?> actual) {
+    return new OptionalSubject(metadata(), actual, "optional");
+  }
+
+  @SuppressWarnings("Java7ApiChecker") // no more dangerous that wherever the user got the Stream
+  public final StreamSubject that(@Nullable Stream<?> actual) {
+    return new StreamSubject(metadata(), actual);
+  }
+
   /**
    * Returns a new instance that will output the given message before the main failure message. If
    * this method is called multiple times, the messages will appear in the order that they were

core/src/test/java/com/google/common/truth/TruthAssertThatTest.java

@@ -25,6 +25,8 @@
 import com.google.common.reflect.TypeToken;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.util.Optional;
+import java.util.stream.Stream;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -45,6 +47,9 @@ public void staticAssertThatMethodsMatchStandardSubjectBuilderInstanceMethods()
     ImmutableSortedSet<TypeToken<?>> verbTypes =
         FluentIterable.from(asList(StandardSubjectBuilder.class.getMethods()))
             .filter(input -> input.getName().equals("that"))
+            // TODO: b/166630734 - Remove this when we add the assertThat overloads.
+            .filter(input -> input.getParameterTypes()[0] != Optional.class)
+            .filter(input -> input.getParameterTypes()[0] != Stream.class)
             .transform(TruthAssertThatTest::methodToReturnTypeToken)
             .toSortedSet(Ordering.usingToString());
     ImmutableSortedSet<TypeToken<?>> truthTypes =