Work around the NPE bug in ClassRemapper of ASM. ASM throws an NPE in

MethodRemapper when MethodRemapper is chained after MethodNode and there is
compressed stack map frame in a method.

RELNOTES: n/a

PiperOrigin-RevId: 152199391

1 files changed, 38 insertions, 2 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/CoreLibraryRewriter.java b/src/tools/android/java/com/google/devtools/build/android/desugar/CoreLibraryRewriter.java
index 4a2510908d..5b63253f7c 100644
--- a/src/tools/android/java/com/google/devtools/build/android/desugar/CoreLibraryRewriter.java
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/CoreLibraryRewriter.java
@@ -19,8 +19,10 @@ import org.objectweb.asm.Attribute;
 import org.objectweb.asm.ClassReader;
 import org.objectweb.asm.ClassVisitor;
 import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.MethodVisitor;
 import org.objectweb.asm.Opcodes;
 import org.objectweb.asm.commons.ClassRemapper;
+import org.objectweb.asm.commons.MethodRemapper;
 import org.objectweb.asm.commons.Remapper;
 
 /** Utility class to prefix or unprefix class names of core library classes */
@@ -112,7 +114,7 @@ class CoreLibraryRewriter {
     @Override
     public void accept(ClassVisitor cv, Attribute[] attrs, int flags) {
       cv =
-          new ClassRemapper(
+          new ClassRemapperWithBugFix(
               cv,
               new Remapper() {
                 @Override
@@ -137,7 +139,7 @@ class CoreLibraryRewriter {
       this.cv = this.writer;
       if (prefix.length() != 0) {
         this.cv =
-            new ClassRemapper(
+            new ClassRemapperWithBugFix(
                 this.cv,
                 new Remapper() {
                   @Override
@@ -152,4 +154,38 @@ class CoreLibraryRewriter {
       return writer.toByteArray();
     }
   }
+
+  /** ClassRemapper subclass to work around b/36654936 (caused by ASM bug 317785) */
+  private static class ClassRemapperWithBugFix extends ClassRemapper {
+
+    public ClassRemapperWithBugFix(ClassVisitor cv, Remapper remapper) {
+      super(cv, remapper);
+    }
+
+    @Override
+    protected MethodVisitor createMethodRemapper(MethodVisitor mv) {
+      return new MethodRemapper(mv, this.remapper) {
+        private final boolean isArrayNullOrEmpty(Object[] array) {
+          return array == null || array.length == 0;
+        }
+
+        @Override
+        public void visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack) {
+          if (isArrayNullOrEmpty(local)) {
+            nLocal = 0;
+          }
+          if (isArrayNullOrEmpty(stack)) {
+            nStack = 0;
+          }
+          /*
+           * In {@code FrameNode.accept(MethodVisitor)}, when the frame is Opcodes.F_CHOP,
+           * it is possible that nLocal is greater than 0, and local is null, which causes
+           * MethodRemapper to throw a NPE. So the patch is to make sure that the
+           * {@code nLocal<=local.length} and {@code nStack<=stack.length}
+           */
+          super.visitFrame(type, nLocal, local, nStack, stack);
+        }
+      };
+    }
+  }
 }