Custom lint class for check for and enforce custom xml headers

MissingXmlHeaderDetector.java

public class MissingXmlHeaderDetector extends ResourceXmlDetector {

    public static final Issue ISSUE_MISSING_XML_HEADER = Issue.create(
            "MissingXmlHeader",
            "Flags xml files that don't have a header.",
            "An xml file should always have the xml header to declare that it is an xml file despite the file ending.",
            Category.CORRECTNESS, 10, Severity.ERROR,
            new Implementation(MissingXmlHeaderDetector.class, Scope.RESOURCE_FILE_SCOPE));

    @Override
    public void visitDocument(XmlContext context, Document document) {
        final String content = context.getClient().readFile(context.file).toString();
        if (!content.startsWith("<?xml")) {
            final LintFix addXmlHeader = fix()
                    .replace()
                    .name("Add xml header")
                    .text(content)
                    .with("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n$content")
                    .autoFix()
                    .build();

            context.report(ISSUE_MISSING_XML_HEADER,
                    document,
                    Location.create(context.file, content, 0, content.length()),
                    "Missing an xml header.",
                    addXmlHeader);
        }
    }
}