ASTPrinter.java

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import java.lang.foreign.*;
import static java.lang.foreign.MemorySegment.NULL;
import static org.llvm.clang.Index_h.*;
import org.llvm.clang.*;

public class ASTPrinter {
    private static String asJavaString(MemorySegment clangStr) {
        String str = clang_getCString(clangStr).getString(0);
        clang_disposeString(clangStr);
        return str;
    }

    public static void main(String[] args) {
        if (args.length == 0) {
            System.err.println("java ASTPrinter <C source or header>");
            System.exit(1);
        }

        try (var arena = Arena.ofConfined()) {
            // parse the C header/source passed from the command line
            var index = clang_createIndex(0, 0);
            var tu = clang_parseTranslationUnit(index, arena.allocateFrom(args[0]),
                    NULL, 0, NULL, 0, CXTranslationUnit_None());
            // array trick to update within lambda
            var level = new int[1];
            var visitor = new MemorySegment[1];

            // clang Cursor visitor callback
            visitor[0] = CXCursorVisitor.allocate((cursor, parent, data) -> {
                var kind = clang_getCursorKind(cursor);
                var name = asJavaString(clang_getCursorSpelling(arena, cursor));
                var kindName = asJavaString(clang_getCursorKindSpelling(arena, kind));
                System.out.printf("%s %s %s", " ".repeat(level[0]), kindName, name);
                var type = clang_getCursorType(arena, cursor);
                if (CXType.kind(type) != CXType_Invalid()) {
                    var typeName = asJavaString(clang_getTypeSpelling(arena, type));
                    System.out.printf(" <%s>", typeName);
                }
                System.out.println();

                // visit children
                level[0]++;
                clang_visitChildren(cursor, visitor[0], NULL);
                level[0]--;

                return CXChildVisit_Continue();
            }, arena);

            // get the AST root and visit it
            var root = clang_getTranslationUnitCursor(arena, tu);
            clang_visitChildren(root, visitor[0], NULL);

            clang_disposeTranslationUnit(tu);
            clang_disposeIndex(index);
        }
    }
}