The `ignore_malformed` option is supported by a few of our field types, mainly numerics and dates, to still accept the document when such fields hold malformed values. See https://www.elastic.co/guide/en/elasticsearch/reference/current/ignore-malformed.html. Also `ignore_malformed` is an index level setting that gets applied to all field types that support it. 

The boolean field type does not support `ignore_malformed` but it should, so that if a boolean field cannot be parsed as a boolean, the document can still be accepted.


server/src/main/java/org/elasticsearch/index/mapper/BooleanFieldMapper.java
return new Builder(simpleName(), scriptCompiler, indexCreatedVersion).init(this);
    }
    @Override
    protected String contentType() {
        return CONTENT_TYPE;
    }
    @Override
    public SourceLoader.SyntheticFieldLoader syntheticFieldLoader() {
        if (hasScript()) {
            return SourceLoader.SyntheticFieldLoader.NOTHING;
        }
        if (hasDocValues == false) {
            throw new IllegalArgumentException(
                "field [" + name() + "] of type [" + typeName() + "] doesn't support synthetic source because it doesn't have doc values"
            );
        }
        if (copyTo.copyToFields().isEmpty() != true) {
            throw new IllegalArgumentException(
                "field [" + name() + "] of type [" + typeName() + "] doesn't support synthetic source because it declares copy_to"
            );
        }
        return new SortedNumericDocValuesSyntheticFieldLoader(name(), simpleName(), false) {
            @Override
            protected void writeValue(XContentBuilder b, long value) throws IOException {
                b.value(value == 1);
            }
        };
    }
}