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
emptyList()
        );
        aliasMapper.validate(mappers);
    }
    public void testFieldAliasWithNestedTarget() {
        ObjectMapper objectMapper = createNestedObjectMapper("nested");
        FieldAliasMapper aliasMapper = new FieldAliasMapper("alias", "alias", "nested.field");
        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> {
            MappingLookup mappers = createMappingLookup(
                singletonList(createFieldMapper("nested", "field")),
                Collections.singletonList(objectMapper),
                singletonList(aliasMapper),
                emptyList()
            );
            aliasMapper.validate(mappers);
        });
        String expectedMessage = "Invalid [path] value [nested.field] for field alias [alias]: "
            + "an alias must have the same nested scope as its target. The alias is not nested, "
            + "but the target's nested scope is [nested].";
        assertEquals(expectedMessage, e.getMessage());
    }
    public void testFieldAliasWithDifferentNestedScopes() {
        FieldAliasMapper aliasMapper = new FieldAliasMapper("alias", "nested2.alias", "nested1.field");
        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> {
            MappingLookup mappers = createMappingLookup(
                singletonList(createFieldMapper("nested1", "field")),
                List.of(createNestedObjectMapper("nested1"), createNestedObjectMapper("nested2")),
                singletonList(aliasMapper),
                emptyList()
            );