private void failField(Context context, Schema schema, ImmutableSDField field) {
        context.illegal("For " + schema + ", field '" + field.getName() +
                        "': match/index:prefix is not supported for indexes.");
    }
match:prefix for indexed fields not supported

@author vegardh
config-model/src/main/java/com/yahoo/vespa/model/application/validation/NoPrefixForIndexes.java