Do not require option converters to be public.

Change how we reflectively instantiate the option converters so that Bazel no longer crashes when we try to use a non-public class. Technically, this is overriding the visibility of the class and the constructor, however this is merely a side effect of the fact that annotations do not allow us to use an actual object.

It is not obvious why these classes have to be public and a mistake here results with Bazel failing to start.

PiperOrigin-RevId: 482281892
Change-Id: I064301ce88f83fd55a305385309cfb357e5e054c

src/main/java/com/google/devtools/common/options/Option.java

@@ -123,9 +123,11 @@
    * an object or a simple type. The default is to use the builtin converters ({@link
    * Converters#DEFAULT_CONVERTERS}). Custom converters must implement the {@link Converter}
    * interface.
+   *
+   * <p>This class will be instantiated reflectively using a nullary constructor. Provided class
+   * does not have to be visible in the {@linkplain com.google.devtools.common.options options}
+   * package, e.g. private classes are allowed.
    */
-  @SuppressWarnings({"unchecked", "rawtypes"})
-  // Can't figure out how to coerce Converter.class into Class<? extends Converter<?>>
   Class<? extends Converter> converter() default Converter.class;
 
   /**

src/main/java/com/google/devtools/common/options/OptionDefinition.java

@@ -238,7 +238,8 @@ public Converter<?> getConverter() {
     } else {
       try {
         // Instantiate the given Converter class.
-        Constructor<?> constructor = converterClass.getConstructor();
+        Constructor<?> constructor = converterClass.getDeclaredConstructor();
+        constructor.setAccessible(true);
         converter = (Converter<?>) constructor.newInstance();
       } catch (SecurityException | IllegalArgumentException | ReflectiveOperationException e) {
         // This indicates an error in the Converter, and should be discovered the first time it is