ijar Kotlin handling

Remove unused handling of the `KeepForCompile` attribute, and instead check for
the `@kotlin.Metadata` annotation and preserve all Kotlin classes.

bazelbuild#4549

RELNOTES: Make ijar / java_import preserve classes with `@kotlin.Metadata` annotations
PiperOrigin-RevId: 441243993

third_party/ijar/classfile.cc

@@ -425,6 +425,7 @@ struct Attribute {
   virtual ~Attribute() {}
   virtual void Write(u1 *&p) = 0;
   virtual void ExtractClassNames() {}
+  virtual bool KeepForCompile() const { return false; }
 
   void WriteProlog(u1 *&p, u2 length) {
     put_u2be(p, attribute_name_->slot());
@@ -434,10 +435,6 @@ struct Attribute {
   Constant *attribute_name_;
 };
 
-struct KeepForCompileAttribute : Attribute {
-  void Write(u1 *&p) { WriteProlog(p, 0); }
-};
-
 struct HasAttrs {
   std::vector<Attribute*> attributes;
 
@@ -1080,6 +1077,15 @@ struct AnnotationsAttribute : Attribute {
     }
   }
 
+  virtual bool KeepForCompile() const {
+    for (auto *annotation : annotations_) {
+      if (annotation->type_->Display() == "Lkotlin/Metadata;") {
+        return true;
+      }
+    }
+    return false;
+  }
+
   void Write(u1 *&p) {
     WriteProlog(p, -1);
     u1 *payload_start = p - 4;
@@ -1410,7 +1416,7 @@ struct ClassFile : HasAttrs {
 
   bool ReadConstantPool(const u1 *&p);
 
-  bool IsExplicitlyKept();
+  bool KeepForCompile();
 
   bool IsLocalOrAnonymous();
 
@@ -1530,10 +1536,6 @@ void HasAttrs::ReadAttrs(const u1 *&p) {
     } else if (attr_name == "PermittedSubclasses") {
       attributes.push_back(
           PermittedSubclassesAttribute::Read(p, attribute_name));
-    } else if (attr_name == "com.google.devtools.ijar.KeepForCompile") {
-      auto attr = new KeepForCompileAttribute;
-      attr->attribute_name_ = attribute_name;
-      attributes.push_back(attr);
     } else {
       // Skip over unknown attributes with a warning.  The JVM spec
       // says this is ok, so long as we handle the mandatory attributes.
@@ -1677,23 +1679,17 @@ bool ClassFile::IsLocalOrAnonymous() {
 
 static bool HasKeepForCompile(const std::vector<Attribute *> attributes) {
   for (const Attribute *attribute : attributes) {
-    if (attribute->attribute_name_->Display() ==
-        "com.google.devtools.ijar.KeepForCompile") {
+    if (attribute->KeepForCompile()) {
       return true;
     }
   }
   return false;
 }
 
-bool ClassFile::IsExplicitlyKept() {
+bool ClassFile::KeepForCompile() {
   if (HasKeepForCompile(attributes)) {
     return true;
   }
-  for (const Member *method : methods) {
-    if (HasKeepForCompile(method->attributes)) {
-      return true;
-    }
-  }
   return false;
 }
 
@@ -1744,12 +1740,6 @@ static ClassFile *ReadClass(const void *classdata, size_t length) {
   for (int ii = 0; ii < methods_count; ++ii) {
     Member *method = Member::Read(p);
 
-    if (HasKeepForCompile(method->attributes)) {
-      // Always keep methods marked as such
-      clazz->methods.push_back(method);
-      continue;
-    }
-
     // drop class initializers
     if (method->name->Display() == "<clinit>") continue;
 
@@ -1950,10 +1940,8 @@ void ClassFile::WriteClass(u1 *&p) {
 bool StripClass(u1 *&classdata_out, const u1 *classdata_in, size_t in_length) {
   ClassFile *clazz = ReadClass(classdata_in, in_length);
   bool keep = true;
-  if (clazz == NULL || clazz->IsExplicitlyKept()) {
+  if (clazz == NULL || clazz->KeepForCompile()) {
     // Class is invalid or kept. Simply copy it to the output and call it a day.
-    // TODO: If kept, only emit methods marked with KeepForCompile attribute,
-    // as opposed to the entire type.
     put_n(classdata_out, classdata_in, in_length);
   } else if (clazz->IsLocalOrAnonymous()) {
     keep = false;

third_party/ijar/test/GenKeepForCompile.java

@@ -16,16 +16,14 @@
 import java.util.jar.JarOutputStream;
 import java.util.zip.ZipEntry;
 import org.objectweb.asm.AnnotationVisitor;
-import org.objectweb.asm.Attribute;
-import org.objectweb.asm.ByteVector;
 import org.objectweb.asm.ClassWriter;
 import org.objectweb.asm.Label;
 import org.objectweb.asm.MethodVisitor;
 import org.objectweb.asm.Opcodes;
 
 /**
- * GenKeepForCompile creates a jarfile containing a class definition that has the KeepForCOmpile
- * attribute.
+ * GenKeepForCompile creates a jarfile containing a class definition that has the kotlin.Metadata
+ * annotation.
  */
 public class GenKeepForCompile implements Opcodes {
 
@@ -62,7 +60,15 @@ public static byte[] dump() throws Exception {
         AnnotationVisitor annotationVisitor1 = annotationVisitor0.visitArray("d1");
         annotationVisitor1.visit(
             null,
-            "\u0000\u0014\n\u0000\n\u0002\u0010\u000e\n\u0002\u0018\u0002\n\u0000\n\u0002\u0018\u0002\n\u0002\u0010\u0008\u001a!\u0010\u0000\u001a\u00020\u0001*\u00020\u00022\u0012\u0010\u0003\u001a\u000e\u0012\u0004\u0012\u00020\u0005\u0012\u0004\u0012\u00020\u00010\u0004H\u0086\u0008");
+            "\u0000\u0014\n"
+                + "\u0000\n"
+                + "\u0002\u0010\u000e\n"
+                + "\u0002\u0018\u0002\n"
+                + "\u0000\n"
+                + "\u0002\u0018\u0002\n"
+                + "\u0002\u0010\u0008\u001a!\u0010\u0000\u001a\u00020\u0001*\u00020\u00022\u0012"
+                + "\u0010\u0003\u001a\u000e\u0012\u0004\u0012\u00020\u0005\u0012\u0004\u0012\u00020"
+                + "\u00010\u0004H\u0086\u0008");
         annotationVisitor1.visitEnd();
       }
       {
@@ -103,17 +109,6 @@ public static byte[] dump() throws Exception {
             methodVisitor.visitParameterAnnotation(1, "Lorg/jetbrains/annotations/NotNull;", false);
         annotationVisitor0.visitEnd();
       }
-      // ATTRIBUTE com.google.devtools.ijar.KeepForCompile
-      // ASM-ifier doesn't emit attributes it does not know about :( - emitting by hand here.
-      methodVisitor.visitAttribute(
-          new Attribute("com.google.devtools.ijar.KeepForCompile") {
-            @Override
-            public ByteVector write(
-                ClassWriter cw, byte[] code, int len, int maxStack, int maxLocals) {
-              // nothing to write, just get the attribute's name in the file.
-              return new ByteVector();
-            }
-          });
 
       methodVisitor.visitCode();
       Label label0 = new Label();

third_party/ijar/test/ijar_test.sh

@@ -576,11 +576,6 @@ function test_keep_for_compile() {
     grep -c "// Method kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull" ||
     true)
   check_eq 2 $lines "Output jar should have kept method body"
-  attr=$($JAVAP -classpath $TEST_TMPDIR/keep.jar -v -p \
-    functions.car.CarInlineUtilsKt |
-    strings |
-    grep -c "com.google.devtools.ijar.KeepForCompile" || true)
-  check_eq 2 $attr "Output jar should have kept KeepForCompile attribute."
 }
 
 function test_central_dir_largest_regular() {