IDEA-130708 Incorrect locals names

src/org/jetbrains/java/decompiler/main/rels/ClassWrapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2016 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -163,7 +163,8 @@ public class ClassWrapper {
       if (DecompilerContext.getOption(IFernflowerPreferences.USE_DEBUG_VAR_NAMES)) {
         StructLocalVariableTableAttribute attr = mt.getLocalVariableAttr();
         if (attr != null) {
-          varProc.setDebugVarNames(attr.getMapVarNames());
+          // only param names here
+          varProc.setDebugVarNames(attr.getMapParamNames());
         }
       }
 

src/org/jetbrains/java/decompiler/modules/decompiler/ExprProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2016 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -341,7 +341,7 @@ public class ExprProcessor implements CodeConstants {
         case opc_fload:
         case opc_dload:
         case opc_aload:
-          pushEx(stack, exprlist, new VarExprent(instr.getOperand(0), varTypes[instr.opcode - opc_iload], varProcessor));
+          pushEx(stack, exprlist, new VarExprent(instr.getOperand(0), varTypes[instr.opcode - opc_iload], varProcessor, bytecode_offset));
           break;
         case opc_iaload:
         case opc_laload:
@@ -371,8 +371,8 @@ public class ExprProcessor implements CodeConstants {
         case opc_astore:
           Exprent top = stack.pop();
           int varindex = instr.getOperand(0);
-          AssignmentExprent assign =
-            new AssignmentExprent(new VarExprent(varindex, varTypes[instr.opcode - opc_istore], varProcessor), top, bytecode_offsets);
+          AssignmentExprent assign = new AssignmentExprent(
+            new VarExprent(varindex, varTypes[instr.opcode - opc_istore], varProcessor, nextMeaningfulOffset(block, i)), top, bytecode_offsets);
           exprlist.add(assign);
           break;
         case opc_iastore:
@@ -624,6 +624,23 @@ public class ExprProcessor implements CodeConstants {
     }
   }
 
+  private static int nextMeaningfulOffset(BasicBlock block, int index) {
+    InstructionSequence seq = block.getSeq();
+    while (++index < seq.length()) {
+      switch (seq.getInstr(index).opcode) {
+        case opc_nop:
+        case opc_istore:
+        case opc_lstore:
+        case opc_fstore:
+        case opc_dstore:
+        case opc_astore:
+          continue;
+      }
+      return block.getOldOffset(index);
+    }
+    return -1;
+  }
+
   private void pushEx(ExprentStack stack, List<Exprent> exprlist, Exprent exprent) {
     pushEx(stack, exprlist, exprent, null);
   }

src/org/jetbrains/java/decompiler/modules/decompiler/exps/FieldExprent.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2016 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -88,7 +88,7 @@ public class FieldExprent extends Exprent {
     if (method != null) {
       StructLocalVariableTableAttribute attr = method.methodStruct.getLocalVariableAttr();
       if (attr != null) {
-        return attr.getMapVarNames().containsValue(name);
+        return attr.containsName(name);
       }
     }
 

src/org/jetbrains/java/decompiler/modules/decompiler/exps/VarExprent.java

@@ -28,6 +28,7 @@ import org.jetbrains.java.decompiler.modules.decompiler.vars.VarProcessor;
 import org.jetbrains.java.decompiler.modules.decompiler.vars.VarTypeProcessor;
 import org.jetbrains.java.decompiler.modules.decompiler.vars.VarVersionPair;
 import org.jetbrains.java.decompiler.struct.attr.StructGeneralAttribute;
+import org.jetbrains.java.decompiler.struct.attr.StructLocalVariableTableAttribute;
 import org.jetbrains.java.decompiler.struct.attr.StructLocalVariableTypeTableAttribute;
 import org.jetbrains.java.decompiler.struct.gen.VarType;
 import org.jetbrains.java.decompiler.struct.gen.generics.GenericFieldDescriptor;
@@ -36,6 +37,7 @@ import org.jetbrains.java.decompiler.struct.match.MatchEngine;
 import org.jetbrains.java.decompiler.struct.match.MatchNode;
 import org.jetbrains.java.decompiler.struct.match.MatchNode.RuleValue;
 import org.jetbrains.java.decompiler.util.InterpreterUtil;
+import org.jetbrains.java.decompiler.util.TextUtil;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -49,15 +51,21 @@ public class VarExprent extends Exprent {
   private VarType varType;
   private boolean definition = false;
   private VarProcessor processor;
+  private final int visibleOffset;
   private int version = 0;
   private boolean classDef = false;
   private boolean stack = false;
 
   public VarExprent(int index, VarType varType, VarProcessor processor) {
+    this(index, varType, processor, -1);
+  }
+
+  public VarExprent(int index, VarType varType, VarProcessor processor, int visibleOffset) {
     super(EXPRENT_VAR);
     this.index = index;
     this.varType = varType;
     this.processor = processor;
+    this.visibleOffset = visibleOffset;
   }
 
   @Override
@@ -77,7 +85,7 @@ public class VarExprent extends Exprent {
 
   @Override
   public Exprent copy() {
-    VarExprent var = new VarExprent(index, getVarType(), processor);
+    VarExprent var = new VarExprent(index, getVarType(), processor, visibleOffset);
     var.setDefinition(definition);
     var.setVersion(version);
     var.setClassDef(classDef);
@@ -97,43 +105,85 @@ public class VarExprent extends Exprent {
       tracer.incrementCurrentSourceLine(buffer.countLines());
     }
     else {
+      VarVersionPair varVersion = new VarVersionPair(index, version);
+      String name = getName(varVersion);
+
+      if (definition) {
+        if (processor != null && processor.getVarFinal(varVersion) == VarTypeProcessor.VAR_EXPLICIT_FINAL) {
+          buffer.append("final ");
+        }
+        appendDefinitionType(buffer, varVersion);
+        buffer.append(" ");
+      }
+
+      buffer.append(name == null ? ("var" + index + (this.version == 0 ? "" : "_" + this.version)) : name);
+    }
+
+    return buffer;
+  }
+
+  private String getName(VarVersionPair varVersion) {
     String name = null;
+    if (DecompilerContext.getOption(IFernflowerPreferences.USE_DEBUG_VAR_NAMES)) {
+      MethodWrapper method = (MethodWrapper)DecompilerContext.getProperty(DecompilerContext.CURRENT_METHOD_WRAPPER);
+      if (method != null) {
+        StructLocalVariableTableAttribute attr = method.methodStruct.getLocalVariableAttr();
+        if (attr != null && processor != null) {
+          Integer index = processor.getVarOriginalIndex(varVersion);
+          if (index != null) {
+            name = attr.getName(index, visibleOffset);
+            if (name != null && TextUtil.isValidIdentifier(name, method.methodStruct.getClassStruct().getBytecodeVersion())) {
+              return name;
+            }
+          }
+        }
+      }
+    }
     if (processor != null) {
-        name = processor.getVarName(new VarVersionPair(index, version));
+      name = processor.getVarName(varVersion);
+    }
+    return name;
   }
 
-      if (definition) {
-        if (processor != null && processor.getVarFinal(new VarVersionPair(index, version)) == VarTypeProcessor.VAR_EXPLICIT_FINAL) {
-          buffer.append("final ");
+  private void appendDefinitionType(TextBuffer buffer, VarVersionPair varVersion) {
+    if (DecompilerContext.getOption(IFernflowerPreferences.USE_DEBUG_VAR_NAMES)) {
+      MethodWrapper method = (MethodWrapper)DecompilerContext.getProperty(DecompilerContext.CURRENT_METHOD_WRAPPER);
+      if (method != null) {
+        Integer originalIndex = null;
+        if (processor != null) {
+          originalIndex = processor.getVarOriginalIndex(varVersion);
         }
-        boolean generic = false;
+        if (originalIndex != null) {
+          // first try from signature
           if (DecompilerContext.getOption(IFernflowerPreferences.DECOMPILE_GENERIC_SIGNATURES)) {
-          MethodWrapper method = (MethodWrapper)DecompilerContext.getProperty(DecompilerContext.CURRENT_METHOD_WRAPPER);
             StructLocalVariableTypeTableAttribute attr = (StructLocalVariableTypeTableAttribute)method.methodStruct.getAttributes()
               .getWithKey(StructGeneralAttribute.ATTRIBUTE_LOCAL_VARIABLE_TYPE_TABLE);
-          if (attr != null && processor != null) {
-            Integer index = processor.getVarOriginalIndex(new VarVersionPair(this.index, version));
-            if (index != null) {
-              String signature = attr.getMapVarSignatures().get(index);
+            if (attr != null) {
+              String signature = attr.getSignature(originalIndex, visibleOffset);
               if (signature != null) {
                 GenericFieldDescriptor descriptor = GenericMain.parseFieldSignature(signature);
                 if (descriptor != null) {
                   buffer.append(GenericMain.getGenericCastTypeName(descriptor.type));
-                  generic = true;
+                  return;
                 }
               }
             }
           }
+
+          // then try from descriptor
+          StructLocalVariableTableAttribute attr = method.methodStruct.getLocalVariableAttr();
+          if (attr != null) {
+            String descriptor = attr.getDescriptor(originalIndex, visibleOffset);
+            if (descriptor != null) {
+              buffer.append(ExprProcessor.getCastTypeName(new VarType(descriptor)));
+              return;
+            }
           }
-        if (!generic) {
-          buffer.append(ExprProcessor.getCastTypeName(getVarType()));
         }
-        buffer.append(" ");
       }
-      buffer.append(name == null ? ("var" + index + (version == 0 ? "" : "_" + version)) : name);
     }
 
-    return buffer;
+    buffer.append(ExprProcessor.getCastTypeName(getVarType()));
   }
 
   @Override

src/org/jetbrains/java/decompiler/modules/decompiler/vars/VarProcessor.java

@@ -40,8 +40,9 @@ public class VarProcessor {
   }
 
   public void setVarVersions(RootStatement root) {
+    VarVersionsProcessor oldProcessor = varVersions;
     varVersions = new VarVersionsProcessor(method, methodDescriptor);
-    varVersions.setVarVersions(root);
+    varVersions.setVarVersions(root, oldProcessor);
   }
 
   public void setVarDefinitions(Statement root) {

src/org/jetbrains/java/decompiler/modules/decompiler/vars/VarVersionsProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2016 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,7 +35,7 @@ import java.util.Map.Entry;
 
 public class VarVersionsProcessor {
   private final StructMethod method;
-  private Map<Integer, Integer> mapOriginalVarIndices = new HashMap<>();
+  private Map<Integer, Integer> mapOriginalVarIndices = Collections.emptyMap();
   private VarTypeProcessor typeProcessor;
 
   public VarVersionsProcessor(StructMethod mt, MethodDescriptor md) {
@@ -43,7 +43,7 @@ public class VarVersionsProcessor {
     typeProcessor = new VarTypeProcessor(mt, md);
   }
 
-  public void setVarVersions(RootStatement root) {
+  public void setVarVersions(RootStatement root, VarVersionsProcessor previousVersionsProcessor) {
     SSAConstructorSparseEx ssa = new SSAConstructorSparseEx();
     ssa.splitVariables(root, method);
 
@@ -60,7 +60,7 @@ public class VarVersionsProcessor {
 
     eliminateNonJavaTypes(typeProcessor);
 
-    setNewVarIndices(typeProcessor, graph);
+    setNewVarIndices(typeProcessor, graph, previousVersionsProcessor);
   }
 
   private static void mergePhiVersions(SSAConstructorSparseEx ssa, DirectGraph graph) {
@@ -227,7 +227,7 @@ public class VarVersionsProcessor {
     }
   }
 
-  private void setNewVarIndices(VarTypeProcessor typeProcessor, DirectGraph graph) {
+  private void setNewVarIndices(VarTypeProcessor typeProcessor, DirectGraph graph, VarVersionsProcessor previousVersionsProcessor) {
     final Map<VarVersionPair, VarType> mapExprentMaxTypes = typeProcessor.getMapExprentMaxTypes();
     Map<VarVersionPair, VarType> mapExprentMinTypes = typeProcessor.getMapExprentMinTypes();
     Map<VarVersionPair, Integer> mapFinalVars = typeProcessor.getMapFinalVars();
@@ -286,8 +286,20 @@ public class VarVersionsProcessor {
       }
     });
 
+    if (previousVersionsProcessor != null) {
+      Map<Integer, Integer> oldIndices = previousVersionsProcessor.getMapOriginalVarIndices();
+      this.mapOriginalVarIndices = new HashMap<>(mapOriginalVarIndices.size());
+      for (Entry<Integer, Integer> entry : mapOriginalVarIndices.entrySet()) {
+        Integer value = entry.getValue();
+        Integer oldValue = oldIndices.get(value);
+        value = oldValue != null ? oldValue : value;
+        this.mapOriginalVarIndices.put(entry.getKey(), value);
+      }
+    }
+    else {
       this.mapOriginalVarIndices = mapOriginalVarIndices;
     }
+  }
 
   public VarType getVarType(VarVersionPair pair) {
     return typeProcessor == null ? null : typeProcessor.getVarType(pair);

src/org/jetbrains/java/decompiler/struct/StructMember.java

@@ -61,7 +61,7 @@ public class StructMember {
         if (StructGeneralAttribute.ATTRIBUTE_LOCAL_VARIABLE_TABLE.equals(name) && attributes.containsKey(name)) {
           // merge all variable tables
           StructLocalVariableTableAttribute table = (StructLocalVariableTableAttribute)attributes.getWithKey(name);
-          table.addLocalVariableTable((StructLocalVariableTableAttribute)attribute);
+          table.add((StructLocalVariableTableAttribute)attribute);
         }
         else if (StructGeneralAttribute.ATTRIBUTE_LOCAL_VARIABLE_TYPE_TABLE.equals(name) && attributes.containsKey(name)) {
           // merge all variable tables

src/org/jetbrains/java/decompiler/struct/attr/StructLocalVariableTableAttribute.java

@@ -19,9 +19,12 @@ import org.jetbrains.java.decompiler.struct.consts.ConstantPool;
 import org.jetbrains.java.decompiler.util.DataInputFullStream;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /*
   u2 local_variable_table_length;
@@ -34,32 +37,70 @@ import java.util.Map;
   }
 */
 public class StructLocalVariableTableAttribute extends StructGeneralAttribute {
-
-  private Map<Integer, String> mapVarNames = Collections.emptyMap();
+  private List<LocalVariable> localVariables = Collections.emptyList();
 
   @Override
   public void initContent(DataInputFullStream data, ConstantPool pool) throws IOException {
     int len = data.readUnsignedShort();
     if (len > 0) {
-      mapVarNames = new HashMap<>(len);
+      localVariables = new ArrayList<>(len);
+
       for (int i = 0; i < len; i++) {
-        data.discard(4);
+        int start_pc = data.readUnsignedShort();
+        int length = data.readUnsignedShort();
         int nameIndex = data.readUnsignedShort();
-        data.discard(2);
+        int descriptorIndex = data.readUnsignedShort();
         int varIndex = data.readUnsignedShort();
-        mapVarNames.put(varIndex, pool.getPrimitiveConstant(nameIndex).getString());
+        localVariables.add(new LocalVariable(start_pc,
+                                             length,
+                                             pool.getPrimitiveConstant(nameIndex).getString(),
+                                             pool.getPrimitiveConstant(descriptorIndex).getString(),
+                                             varIndex));
       }
     }
     else {
-      mapVarNames = Collections.emptyMap();
+      localVariables = Collections.emptyList();
+    }
+  }
+
+  public void add(StructLocalVariableTableAttribute attr) {
+    localVariables.addAll(attr.localVariables);
+  }
+
+  public String getName(int index, int visibleOffset) {
+    return matchingVars(index, visibleOffset).map(v -> v.name).findFirst().orElse(null);
   }
+
+  public String getDescriptor(int index, int visibleOffset) {
+    return matchingVars(index, visibleOffset).map(v -> v.descriptor).findFirst().orElse(null);
+  }
+
+  private Stream<LocalVariable> matchingVars(int index, int visibleOffset) {
+    return localVariables.stream()
+      .filter(v -> v.index == index && (visibleOffset >= v.start_pc && visibleOffset < v.start_pc + v.length));
   }
 
-  public void addLocalVariableTable(StructLocalVariableTableAttribute attr) {
-    mapVarNames.putAll(attr.getMapVarNames());
+  public boolean containsName(String name) {
+    return localVariables.stream().anyMatch(v -> v.name == name);
   }
 
-  public Map<Integer, String> getMapVarNames() {
-    return mapVarNames;
+  public Map<Integer, String> getMapParamNames() {
+    return localVariables.stream().filter(v -> v.start_pc == 0).collect(Collectors.toMap(v -> v.index, v -> v.name, (n1, n2) -> n2));
+  }
+
+  private static class LocalVariable {
+    final int start_pc;
+    final int length;
+    final String name;
+    final String descriptor;
+    final int index;
+
+    private LocalVariable(int start_pc, int length, String name, String descriptor, int index) {
+      this.start_pc = start_pc;
+      this.length = length;
+      this.name = name;
+      this.descriptor = descriptor;
+      this.index = index;
+    }
   }
 }

src/org/jetbrains/java/decompiler/struct/attr/StructLocalVariableTypeTableAttribute.java

@@ -19,9 +19,7 @@ import org.jetbrains.java.decompiler.struct.consts.ConstantPool;
 import org.jetbrains.java.decompiler.util.DataInputFullStream;
 
 import java.io.IOException;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.Map;
+import java.util.Set;
 
 /*
   u2 local_variable_type_table_length;
@@ -33,31 +31,19 @@ import java.util.Map;
     } local_variable_type_table[local_variable_type_table_length];
 */
 public class StructLocalVariableTypeTableAttribute extends StructGeneralAttribute {
-
-  private Map<Integer, String> mapVarSignatures = Collections.emptyMap();
+  // store signature instead of descriptor
+  private final StructLocalVariableTableAttribute backingAttribute = new StructLocalVariableTableAttribute();
 
   @Override
   public void initContent(DataInputFullStream data, ConstantPool pool) throws IOException {
-    int len = data.readUnsignedShort();
-    if (len > 0) {
-      mapVarSignatures = new HashMap<>(len);
-      for (int i = 0; i < len; i++) {
-        data.discard(6);
-        int signatureIndex = data.readUnsignedShort();
-        int varIndex = data.readUnsignedShort();
-        mapVarSignatures.put(varIndex, pool.getPrimitiveConstant(signatureIndex).getString());
-      }
-    }
-    else {
-      mapVarSignatures = Collections.emptyMap();
-    }
+    backingAttribute.initContent(data, pool);
   }
 
   public void add(StructLocalVariableTypeTableAttribute attr) {
-    mapVarSignatures.putAll(attr.getMapVarSignatures());
+    backingAttribute.add(attr.backingAttribute);
   }
 
-  public Map<Integer, String> getMapVarSignatures() {
-    return mapVarSignatures;
+  public String getSignature(int index, int visibleOffset) {
+    return backingAttribute.getDescriptor(index, visibleOffset);
   }
 }

test/org/jetbrains/java/decompiler/SingleClassesTest.java

@@ -93,6 +93,7 @@ public class SingleClassesTest {
   @Test public void testIllegalVarName() { doTest("pkg/TestIllegalVarName"); }
   @Test public void testKotlinConstructor() { doTest("pkg/TestKotlinConstructorKt"); }
   @Test public void testAsserts() { doTest("pkg/TestAsserts"); }
+  @Test public void testLocalsNames() { doTest("pkg/TestLocalsNames"); }
 
   private void doTest(String testFile, String... companionFiles) {
     ConsoleDecompiler decompiler = fixture.getDecompiler();

testData/bulk/pkg/res/Loader.java

@@ -11,9 +11,9 @@ public class Loader {
          throw new RuntimeException("Resource missing");
       } else {
          try {
-            File e = new File(resource.toURI());
-            byte[] bytes = new byte[(int)e.length()];
-            FileInputStream stream = new FileInputStream(e);
+            File file = new File(resource.toURI());
+            byte[] bytes = new byte[(int)file.length()];
+            FileInputStream stream = new FileInputStream(file);
             stream.read(bytes);
             stream.close();
             return new String(bytes, "UTF-8");

testData/results/TestAmbiguousCallWithDebugInfo.dec

@@ -11,7 +11,7 @@ class TestAmbiguousCall {
       IllegalArgumentException iae = new IllegalArgumentException();// 8
       this.m1((RuntimeException)iae, "RE");// 9
       this.m1(iae, "IAE");// 10
-      IllegalArgumentException re = new IllegalArgumentException();// 12
+      RuntimeException re = new IllegalArgumentException();// 12
       this.m1((RuntimeException)re, "RE");// 13
       this.m1((IllegalArgumentException)re, "IAE");// 14
    }// 15

testData/results/TestLocalsNames.dec

@@ -0,0 +1,77 @@
+package pkg;
+
+import java.io.File;
+
+public class TestLocalsNames {
+   private static void rename(File file, boolean recursively) {
+      if(file.isDirectory()) {// 22
+         long start = System.currentTimeMillis();// 23
+         File[] files = file.listFiles();// 25
+         File[] var5 = files;
+         int var6 = files.length;
+
+         for(int var7 = 0; var7 < var6; ++var7) {// 26
+            File s = var5[var7];
+            File dest = new File(s.getAbsolutePath() + ".tmp");// 27
+
+            assert s.renameTo(dest) : "unable to rename " + s + " to " + dest;// 28
+         }
+
+         long elapsed = System.currentTimeMillis() - start;// 31
+         System.out.println("took " + elapsed + "ms (" + elapsed / (long)files.length + "ms per dir)");// 32
+      }
+
+   }// 34
+}
+
+class 'pkg/TestLocalsNames' {
+   method 'rename (Ljava/io/File;Z)V' {
+      1      6
+      4      6
+      7      7
+      a      7
+      c      8
+      f      8
+      13      9
+      17      10
+      18      10
+      1a      12
+      1b      12
+      21      12
+      28      13
+      29      13
+      38      14
+      3e      14
+      43      14
+      49      14
+      55      16
+      66      16
+      70      16
+      7a      16
+      81      12
+      87      19
+      8b      19
+      8c      19
+      8e      20
+      98      20
+      a2      20
+      ab      20
+      ac      20
+      ad      20
+      b1      20
+      b6      20
+      b9      20
+      bc      23
+   }
+}
+
+Lines mapping:
+22 <-> 7
+23 <-> 8
+25 <-> 9
+26 <-> 13
+27 <-> 15
+28 <-> 17
+31 <-> 20
+32 <-> 21
+34 <-> 24

testData/src/pkg/TestLocalsNames.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2000-2016 JetBrains s.r.o.
+ *
+ * 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 pkg;
+
+import java.io.File;
+
+public class TestLocalsNames {
+  private static void rename(File file, boolean recursively) {
+    if (file.isDirectory()) {
+      long start = System.currentTimeMillis();
+
+      File[] files = file.listFiles();
+      for (File s : files) {
+        File dest = new File(s.getAbsolutePath() + ".tmp");
+        assert s.renameTo(dest) : "unable to rename " + s + " to " + dest;
+      }
+
+      long elapsed = System.currentTimeMillis() - start;
+      System.out.println("took " + elapsed + "ms (" + elapsed / files.length + "ms per dir)");
+    }
+  }
+}