Add static analysis to prevent calling liteProtoSubject.isEqualTo(Builder) (and un-deprecate those methods at the same time since they're now uncallable).

extensions/liteproto/src/main/java/com/google/common/truth/extensions/proto/LiteProtoSubject.java

@@ -124,31 +124,23 @@ public void isEqualTo(@Nullable Object expected) {
   }
 
   /**
-   * @deprecated A Builder can never compare equal to a MessageLite instance. Use {@code build()},
-   *     or {@code buildPartial()} on the argument to get a MessageLite for comparison instead. Or,
-   *     if you are passing {@code null}, use {@link #isNull()}.
+   * <b>DO NOT CALL THIS METHOD!</b>. A {@link MessageLite.Builder} will never compare equal to a
+   * MessageLite instance. Use {@code build()}, or {@code buildPartial()} on the argument to get a
+   * MessageLite for comparison instead. Or, if you are passing {@code null}, use {@link #isNull()}.
    */
   /*
-   * TODO(cpovirk): Consider @DoNotCall -- or probably some other static analysis, given the problem
-   * discussed in the rest of this comment.
-   *
-   * The problem: isEqualTo(null) resolves to this overload (since this overload is more specific
-   * than isEqualTo(Object)), so @DoNotCall would break all assertions of that form.
+   * NOTE: we don't actually mark this as deprecated (or @DoNotCall) because isEqualTo(null)
+   * resolves to this overload (since this overload is more specific than isEqualTo(Object)).
    *
    * To address that, we could try also adding something like `<NullT extends Impossible &
    * MessageLite.Builder> void isEqualTo(NullT)` and hoping that isEqualTo(null) would resolve to
    * that instead. That would also have the benefit of making isEqualTo(null) not produce a
    * deprecation warning (though of course people "should" use isNull(): b/17294077). But yuck.
    *
-   * Given the null issue, maybe we should never have added this overload in the first place,
-   * instead adding static analysis specific to MessageLite-MessageLite.Builder comparisons. (Sadly,
-   * we can't remove it now without breaking binary compatibility.)
-   *
-   * Still, we could add static analysis to produce a compile error for isEqualTo(Builder) this even
-   * today, even without using @DoNotCall. And then we could consider removing @Deprecated to stop
-   * spamming the people who call isEqualTo(null).
+   * Given the null issue, maybe we should never have added this overload in the first place!
+   * In cl/839267698, we added static analysis to MessageLite-MessageLite.Builder comparisons.
+   * However, we cannot remove this method without breaking binary compatibility.
    */
-  @Deprecated
   public void isEqualTo(MessageLite.@Nullable Builder builder) {
     isEqualTo((Object) builder);
   }
@@ -175,12 +167,11 @@ public void isNotEqualTo(@Nullable Object expected) {
   }
 
   /**
-   * @deprecated A Builder will never compare equal to a MessageLite instance. Use {@code build()},
-   *     or {@code buildPartial()} on the argument to get a MessageLite for comparison instead. Or,
-   *     if you are passing {@code null}, use {@link #isNotNull()}.
+   * <b>DO NOT CALL THIS METHOD!</b>. A {@link MessageLite.Builder} will never compare equal to a
+   * {@link MessageLite} instance. Use {@code build()}, or {@code buildPartial()} on the argument to
+   * get a {@link MessageLite} for comparison instead. Or, if you are passing {@code null}, use
+   * {@link #isNotNull()}.
    */
-  // TODO(cpovirk): Consider @DoNotCall or other static analysis. (See isEqualTo(Builder).)
-  @Deprecated
   public void isNotEqualTo(MessageLite.@Nullable Builder builder) {
     isNotEqualTo((Object) builder);
   }

extensions/liteproto/src/test/java/com/google/common/truth/extensions/proto/LiteProtoSubjectTest.java

@@ -161,6 +161,7 @@ public void subjectMethods() {
   }
 
   @Test
+  @SuppressWarnings("DoNotCall")
   public void isEqualTo_success() {
     expectThat(null).isEqualTo(null);
     expectThat(null).isNull();