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/test/java/org/elasticsearch/index/mapper/FieldAliasMapperValidationTests.java
public void testDuplicateFieldAliasAndObject() {
        ObjectMapper objectMapper = createObjectMapper("some.path");
        FieldAliasMapper aliasMapper = new FieldAliasMapper("path", "some.path", "field");
        MapperParsingException e = expectThrows(
            MapperParsingException.class,
            () -> createMappingLookup(emptyList(), singletonList(objectMapper), singletonList(aliasMapper), emptyList())
        );
        assertEquals("Alias [some.path] is defined both as an object and an alias", e.getMessage());
    }
    public void testDuplicateFieldAliasAndConcreteField() {
        FieldMapper field = new MockFieldMapper("field");