[java-decompiler] skips illegal local variable names

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

@@ -21,6 +21,7 @@ import org.jetbrains.java.decompiler.modules.decompiler.stats.Statement;
 import org.jetbrains.java.decompiler.struct.StructMethod;
 import org.jetbrains.java.decompiler.struct.gen.MethodDescriptor;
 import org.jetbrains.java.decompiler.struct.gen.VarType;
+import org.jetbrains.java.decompiler.util.TextUtil;
 
 import java.util.*;
 import java.util.Map.Entry;
@@ -64,8 +65,11 @@ public class VarProcessor {
       String name = mapVarNames.get(pair);
 
       Integer index = mapOriginalVarIndices.get(pair.var);
-      if (index != null && mapDebugVarNames.containsKey(index)) {
+      if (index != null) {
-        name = mapDebugVarNames.get(index);
+        String debugName = mapDebugVarNames.get(index);
+        if (debugName != null && TextUtil.isValidIdentifier(debugName, method.getClassStruct().getBytecodeVersion())) {
+          name = debugName;
+        }
       }
 
       Integer counter = mapNames.get(name);

src/org/jetbrains/java/decompiler/util/TextUtil.java

@@ -15,13 +15,23 @@
  */
 package org.jetbrains.java.decompiler.util;
 
+import org.jetbrains.java.decompiler.code.CodeConstants;
 import org.jetbrains.java.decompiler.main.ClassesProcessor;
 import org.jetbrains.java.decompiler.main.DecompilerContext;
 import org.jetbrains.java.decompiler.main.TextBuffer;
 import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences;
 import org.jetbrains.java.decompiler.modules.decompiler.ExprProcessor;
 
+import java.util.Arrays;
+import java.util.HashSet;
+
 public class TextUtil {
+  private static final HashSet<String> KEYWORDS = new HashSet<>(Arrays.asList(
+    "abstract", "default", "if", "private", "this", "boolean", "do", "implements", "protected", "throw", "break", "double", "import",
+    "public", "throws", "byte", "else", "instanceof", "return", "transient", "case", "extends", "int", "short", "try", "catch", "final",
+    "interface", "static", "void", "char", "finally", "long", "strictfp", "volatile", "class", "float", "native", "super", "while",
+    "const", "for", "new", "switch", "continue", "goto", "package", "synchronized", "true", "false", "null", "assert"));
+
   public static void writeQualifiedSuper(TextBuffer buf, String qualifier) {
     ClassesProcessor.ClassNode classNode = (ClassesProcessor.ClassNode)DecompilerContext.getProperty(DecompilerContext.CURRENT_CLASS_NODE);
     if (!qualifier.equals(classNode.classStruct.qualifiedName)) {
@@ -51,4 +61,26 @@ public class TextUtil {
     sTemp = ("0000" + sTemp).substring(sTemp.length());
     return "\\u" + sTemp;
   }
+
+  public static boolean isValidIdentifier(String id, int version) {
+    return isJavaIdentifier(id) && !isKeyword(id, version);
+  }
+
+  private static boolean isJavaIdentifier(String id) {
+    if (id.isEmpty() || !Character.isJavaIdentifierStart(id.charAt(0))) {
+      return false;
+    }
+
+    for (int i = 1; i < id.length(); i++) {
+      if (!Character.isJavaIdentifierPart(id.charAt(i))) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  private static boolean isKeyword(String id, int version) {
+    return KEYWORDS.contains(id) || version > CodeConstants.BYTECODE_JAVA_5 && "enum".equals(id);
+  }
 }

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

@@ -86,6 +86,7 @@ public class SingleClassesTest {
   @Test public void testStaticNameClash() { doTest("pkg/TestStaticNameClash"); }
   @Test public void testExtendingSubclass() { doTest("pkg/TestExtendingSubclass"); }
   @Test public void testSyntheticAccess() { doTest("pkg/TestSyntheticAccess"); }
+  @Test public void testIllegalVarName() { doTest("pkg/TestIllegalVarName"); }
 
   private void doTest(String testFile, String... companionFiles) {
     ConsoleDecompiler decompiler = fixture.getDecompiler();

testData/results/TestIllegalVarName.dec

@@ -0,0 +1,33 @@
+package pkg;
+
+import kotlin.Metadata;
+import kotlin.jvm.internal.Intrinsics;
+import org.jetbrains.annotations.NotNull;
+
+@Metadata(
+   mv = {1, 1, 0},
+   bv = {1, 0, 0},
+   k = 1,
+   d1 = {"\u0000\u001a\n\u0002\u0018\u0002\n\u0002\u0010\u0000\n\u0002\b\u0002\n\u0002\u0010\u000e\n\u0002\b\u0002\n\u0002\u0010\b\n\u0000\u0018\u00002\u00020\u0001B\u0005¢\u0006\u0002\u0010\u0002J\u0016\u0010\u0003\u001a\u00020\u00042\u0006\u0010\u0005\u001a\u00020\u00042\u0006\u0010\u0006\u001a\u00020\u0007¨\u0006\b"},
+   d2 = {"Lpkg/TestIllegalVarName;", "", "()V", "m", "", "this", "enum", "", "java-decompiler-plugin"}
+)
+public final class TestIllegalVarName {
+   @NotNull
+   public final String m(@NotNull String var1, int var2) {
+      Intrinsics.checkParameterIsNotNull(var1, "this");
+      return var1 + '/' + var2;// 5
+   }
+}
+
+class 'pkg/TestIllegalVarName' {
+   method 'm (Ljava/lang/String;I)Ljava/lang/String;' {
+      1      16
+      3      16
+      11      17
+      1a      17
+      1d      17
+   }
+}
+
+Lines mapping:
+5 <-> 18

testData/src/pkg/TestIllegalVarName.kt

@@ -0,0 +1,7 @@
+package pkg
+
+class TestIllegalVarName {
+  fun m(`this`: String, `enum`: Int): String {
+    return `this` + '/' + `enum`
+  }
+}