Remove getSuperclass() from the j2kt API, as it's not supported and i…

…deally we'd see that at build time.

Also address one use case in Truth by moving the corresponding platform check to Platform.java and adding platform overloads.

RELNOTES=n/a
PiperOrigin-RevId: 588404095

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

@@ -362,4 +362,11 @@ static boolean kotlinRangeContains(Iterable<?> haystack, @Nullable Object needle
               throw newLinkageError(e);
             }
           });
+
+  static boolean classMetadataUnsupported() {
+    // https://github.com/google/truth/issues/198
+    // TODO(cpovirk): Consider whether to remove instanceof tests under GWT entirely.
+    // TODO(cpovirk): Run more Truth tests under GWT, and add tests for this.
+    return false;
+  }
 }

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

@@ -299,7 +299,7 @@ public void isInstanceOf(Class<?> clazz) {
       return;
     }
     if (!isInstanceOfType(actual, clazz)) {
-      if (classMetadataUnsupported()) {
+      if (Platform.classMetadataUnsupported()) {
         throw new UnsupportedOperationException(
             actualCustomStringRepresentation()
                 + ", an instance of "
@@ -320,7 +320,7 @@ public void isNotInstanceOf(Class<?> clazz) {
     if (clazz == null) {
       throw new NullPointerException("clazz");
     }
-    if (classMetadataUnsupported()) {
+    if (Platform.classMetadataUnsupported()) {
       throw new UnsupportedOperationException(
           "isNotInstanceOf is not supported under -XdisableClassMetadata");
     }
@@ -1185,13 +1185,6 @@ private static String typeDescriptionOrGuess(
     return UPPER_CAMEL.to(LOWER_CAMEL, actualClass);
   }
 
-  private static boolean classMetadataUnsupported() {
-    // https://github.com/google/truth/issues/198
-    // TODO(cpovirk): Consider whether to remove instanceof tests under GWT entirely.
-    // TODO(cpovirk): Run more Truth tests under GWT, and add tests for this.
-    return String.class.getSuperclass() == null;
-  }
-
   private void doFail(ImmutableList<Fact> facts) {
     checkNotNull(metadata).fail(facts);
   }

core/src/main/java/com/google/common/truth/super/com/google/common/truth/Platform.java

@@ -268,5 +268,9 @@ static boolean isKotlinRange(Iterable<?> iterable) {
   static boolean kotlinRangeContains(Iterable<?> haystack, @Nullable Object needle) {
     throw new AssertionError(); // never called under GWT because isKotlinRange returns false
   }
+
+  static boolean classMetadataUnsupported() {
+    return String.class.getSuperclass() == null;
+  }
 }