Default and static interface desugaring

RELNOTES: n/a

PiperOrigin-RevId: 153735445

1 files changed, 225 insertions, 0 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/DefaultMethodClassFixer.java b/src/tools/android/java/com/google/devtools/build/android/desugar/DefaultMethodClassFixer.java
new file mode 100644
index 0000000000..a9e86a1575
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/DefaultMethodClassFixer.java
@@ -0,0 +1,225 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.android.desugar;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
+
+import com.google.common.collect.ImmutableList;
+import java.util.HashSet;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.Type;
+
+/**
+ * Fixer of classes that extend interfaces with default methods to declare any missing methods
+ * explicitly and call the corresponding companion method generated by {@link InterfaceDesugaring}.
+ */
+public class DefaultMethodClassFixer extends ClassVisitor {
+
+  private final ClassReaderFactory classpath;
+  private final ClassReaderFactory bootclasspath;
+  private final HashSet<String> instanceMethods = new HashSet<>();
+  private final HashSet<String> seenInterfaces = new HashSet<>();
+
+  private boolean isInterface;
+  private ImmutableList<String> interfaces;
+  private String superName;
+
+  public DefaultMethodClassFixer(ClassVisitor dest, ClassReaderFactory classpath,
+      ClassReaderFactory bootclasspath) {
+    super(Opcodes.ASM5, dest);
+    this.classpath = classpath;
+    this.bootclasspath = bootclasspath;
+  }
+
+  @Override
+  public void visit(
+      int version,
+      int access,
+      String name,
+      String signature,
+      String superName,
+      String[] interfaces) {
+    checkState(this.interfaces == null);
+    isInterface = BitFlags.isSet(access, Opcodes.ACC_INTERFACE);
+    checkArgument(superName != null || "java/lang/Object".equals(name), // ASM promises this
+        "Type without superclass: %s", name);
+    this.interfaces = ImmutableList.copyOf(interfaces);
+    this.superName = superName;
+    super.visit(version, access, name, signature, superName, interfaces);
+  }
+
+  @Override
+  public void visitEnd() {
+    if (!isInterface && !interfaces.isEmpty()) {
+      // Inherited methods take precedence over default methods, so visit all superclasses and
+      // figure out what methods they declare before stubbing in any missing default methods.
+      recordInheritedMethods();
+      stubMissingDefaultMethods(interfaces);
+    }
+    super.visitEnd();
+  }
+
+  @Override
+  public MethodVisitor visitMethod(
+      int access, String name, String desc, String signature, String[] exceptions) {
+    // Keep track of instance methods implemented in this class for later.
+    if (!isInterface && !interfaces.isEmpty()) {
+      recordIfInstanceMethod(access, name, desc);
+    }
+    return super.visitMethod(access, name, desc, signature, exceptions);
+  }
+
+  private void recordInheritedMethods() {
+    InstanceMethodRecorder recorder = new InstanceMethodRecorder();
+    String internalName = superName;
+    while (internalName != null) {
+      ClassReader bytecode = bootclasspath.readIfKnown(internalName);
+      if (bytecode == null) {
+        bytecode = checkNotNull(classpath.readIfKnown(internalName), "Not found: %s", internalName);
+      }
+      bytecode.accept(recorder, ClassReader.SKIP_CODE | ClassReader.SKIP_DEBUG);
+      internalName = bytecode.getSuperName();
+    }
+  }
+
+  private void recordIfInstanceMethod(int access, String name, String desc) {
+    if (BitFlags.noneSet(access, Opcodes.ACC_STATIC)) {
+      // Record all declared instance methods, including abstract, bridge, and native methods, as
+      // they all take precedence over default methods.
+      instanceMethods.add(name + ":" + desc);
+    }
+  }
+
+  private void stubMissingDefaultMethods(ImmutableList<String> interfaces) {
+    for (String implemented : interfaces) {
+      if (!seenInterfaces.add(implemented)) {
+        // Skip: a superclass already implements this interface, or we've seen it here
+        continue;
+      }
+      ClassReader bytecode = classpath.readIfKnown(implemented);
+      if (bytecode != null && !bootclasspath.isKnown(implemented)) {
+        // Class in classpath and bootclasspath is a bad idea but in any event, assume the
+        // bootclasspath will take precedence like in a classloader.
+        // We can skip code attributes as we just need to find default methods to stub.
+        bytecode.accept(new DefaultMethodStubber(), ClassReader.SKIP_CODE | ClassReader.SKIP_DEBUG);
+      }
+    }
+  }
+
+  /**
+   * Visitor for interfaces that produces delegates in the class visited by the outer
+   * {@link DefaultMethodClassFixer} for every default method encountered.
+   */
+  public class DefaultMethodStubber extends ClassVisitor {
+
+    @SuppressWarnings("hiding") private ImmutableList<String> interfaces;
+    private String interfaceName;
+
+    public DefaultMethodStubber() {
+      super(Opcodes.ASM5);
+    }
+
+    @Override
+    public void visit(
+        int version,
+        int access,
+        String name,
+        String signature,
+        String superName,
+        String[] interfaces) {
+      checkArgument(BitFlags.isSet(access, Opcodes.ACC_INTERFACE));
+      checkState(this.interfaces == null);
+      this.interfaces = ImmutableList.copyOf(interfaces);
+      interfaceName = name;
+    }
+
+    @Override
+    public void visitEnd() {
+      stubMissingDefaultMethods(this.interfaces);
+    }
+
+    @Override
+    public MethodVisitor visitMethod(
+        int access, String name, String desc, String signature, String[] exceptions) {
+      if (BitFlags.noneSet(access, Opcodes.ACC_ABSTRACT | Opcodes.ACC_STATIC | Opcodes.ACC_BRIDGE)
+          && instanceMethods.add(name + ":" + desc)) {
+        // Add this method to the class we're desugaring and stub in a body to call the default
+        // implementation in the interface's companion class. ijar omits these methods when setting
+        // ACC_SYNTHETIC modifier, so don't. Don't do this for bridge methods, which we handle
+        // separately.
+        // Signatures can be wrong, e.g., when type variables are introduced, instantiated, or
+        // refined in the class we're processing, so drop them.
+        MethodVisitor stubMethod =
+            DefaultMethodClassFixer.this.visitMethod(access, name, desc, (String) null, exceptions);
+
+        int slot = 0;
+        stubMethod.visitVarInsn(Opcodes.ALOAD, slot++); // load the receiver
+        Type neededType = Type.getMethodType(desc);
+        for (Type arg : neededType.getArgumentTypes()) {
+          stubMethod.visitVarInsn(arg.getOpcode(Opcodes.ILOAD), slot);
+          slot += arg.getSize();
+        }
+        stubMethod.visitMethodInsn(
+            Opcodes.INVOKESTATIC,
+            interfaceName + InterfaceDesugaring.COMPANION_SUFFIX,
+            name,
+            InterfaceDesugaring.companionDefaultMethodDescriptor(interfaceName, desc),
+            /*itf*/ false);
+        stubMethod.visitInsn(neededType.getReturnType().getOpcode(Opcodes.IRETURN));
+
+        stubMethod.visitMaxs(0, 0); // rely on class writer to compute these
+        stubMethod.visitEnd();
+      }
+      return null; // we don't care about the actual code in these methods
+    }
+  }
+
+  private class InstanceMethodRecorder extends ClassVisitor {
+
+    public InstanceMethodRecorder() {
+      super(Opcodes.ASM5);
+    }
+
+    @Override
+    public void visit(
+        int version,
+        int access,
+        String name,
+        String signature,
+        String superName,
+        String[] interfaces) {
+      checkArgument(BitFlags.noneSet(access, Opcodes.ACC_INTERFACE));
+      for (String inheritedInterface : interfaces) {
+        // No point copying default methods that we'll also copy for a superclass.  Note we may
+        // be processing a class in the bootclasspath, in which case the interfaces must also
+        // be in the bootclasspath and we can skip those as well.  Also note this is best-effort,
+        // since these interfaces may extend other interfaces that we're not recording here.
+        seenInterfaces.add(inheritedInterface);
+      }
+      super.visit(version, access, name, signature, superName, interfaces);
+    }
+
+    @Override
+    public MethodVisitor visitMethod(
+        int access, String name, String desc, String signature, String[] exceptions) {
+      recordIfInstanceMethod(access, name, desc);
+      return null;
+    }
+  }
+}