fix: remove invalid chars from class names (#453)

jadx-core/src/main/java/jadx/core/deobf/Deobfuscator.java

@@ -483,21 +483,7 @@ public class Deobfuscator {
 		if (name.length() > maxLength) {
 			return "x" + Integer.toHexString(name.hashCode());
 		}
-		if (!NameMapper.isAllCharsPrintable(name)) {
-			return removeInvalidChars(name);
-		}
-		return name;
-	}
-
-	private String removeInvalidChars(String name) {
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < name.length(); i++) {
-			int ch = name.charAt(i);
-			if (NameMapper.isPrintableChar(ch)) {
-				sb.append((char) ch);
-			}
-		}
-		return sb.toString();
+		return NameMapper.removeInvalidCharsMiddle(name);
 	}
 
 	private void dumpClassAlias(ClassNode cls) {

jadx-core/src/main/java/jadx/core/deobf/NameMapper.java

@@ -91,6 +91,14 @@ public class NameMapper {
 				&& isAllCharsPrintable(str);
 	}
 
+	public static boolean isValidIdentifierStart(int codePoint) {
+		return Character.isJavaIdentifierStart(codePoint);
+	}
+
+	public static boolean isValidIdentifierPart(int codePoint) {
+		return Character.isJavaIdentifierPart(codePoint);
+	}
+
 	public static boolean isPrintableChar(int c) {
 		return 32 <= c && c <= 126;
 	}
@@ -105,6 +113,49 @@ public class NameMapper {
 		return true;
 	}
 
+	/**
+	 * Return modified string with removed:
+	 * <p><ul>
+	 * <li> not printable chars (including unicode)
+	 * <li> chars not valid for java identifier part
+	 * </ul><p>
+	 * Note: this 'middle' method must be used with prefixed string:
+	 * <p><ul>
+	 * <li> can leave invalid chars for java identifier start (i.e numbers)
+	 * <li> result not checked for reserved words
+	 * </ul><p>
+	 */
+	public static String removeInvalidCharsMiddle(String name) {
+		if (isValidIdentifier(name) && isAllCharsPrintable(name)) {
+			return name;
+		}
+		int len = name.length();
+		StringBuilder sb = new StringBuilder(len);
+		for (int i = 0; i < len; i++) {
+			int codePoint = name.codePointAt(i);
+			if (isPrintableChar(codePoint) && isValidIdentifierPart(codePoint)) {
+				sb.append((char) codePoint);
+			}
+		}
+		return sb.toString();
+	}
+
+	/**
+	 * Return string with removed invalid chars, see {@link #removeInvalidCharsMiddle}
+	 * <p>
+	 * Prepend prefix if first char is not valid as java identifier start char.
+	 */
+	public static String removeInvalidChars(String name, String prefix) {
+		String result = removeInvalidCharsMiddle(name);
+		if (!result.isEmpty()) {
+			int codePoint = result.codePointAt(0);
+			if (!isValidIdentifierStart(codePoint)) {
+				return prefix + result;
+			}
+		}
+		return result;
+	}
+
 	private NameMapper() {
 	}
 }

jadx-core/src/main/java/jadx/core/dex/visitors/RenameVisitor.java

@@ -72,14 +72,9 @@ public class RenameVisitor extends AbstractVisitor {
 		ClassInfo classInfo = cls.getClassInfo();
 		ClassInfo alias = classInfo.getAlias();
 		String clsName = alias.getShortName();
-		String newShortName = null;
-		char firstChar = clsName.charAt(0);
-		if (Character.isDigit(firstChar)) {
-			newShortName = Consts.ANONYMOUS_CLASS_PREFIX + clsName;
-		} else if (firstChar == '$') {
-			newShortName = "C" + clsName;
-		}
-		if (newShortName != null) {
+
+		String newShortName = fixClsShortName(clsName);
+		if (!newShortName.equals(clsName)) {
 			classInfo.rename(cls.root(), alias.makeFullClsName(newShortName, true));
 		}
 		if (alias.getPackage().isEmpty()) {
@@ -89,6 +84,17 @@ public class RenameVisitor extends AbstractVisitor {
 		}
 	}
 
+	private String fixClsShortName(String clsName) {
+		char firstChar = clsName.charAt(0);
+		if (Character.isDigit(firstChar)) {
+			return Consts.ANONYMOUS_CLASS_PREFIX + NameMapper.removeInvalidCharsMiddle(clsName);
+		}
+		if (firstChar == '$') {
+			return 'C' + NameMapper.removeInvalidCharsMiddle(clsName);
+		}
+		return NameMapper.removeInvalidChars(clsName, "C");
+	}
+
 	private void checkFields(ClassNode cls) {
 		Set<String> names = new HashSet<>();
 		for (FieldNode field : cls.getFields()) {

jadx-core/src/test/java/jadx/core/deobf/NameMapperTest.java

@@ -0,0 +1,38 @@
+package jadx.core.deobf;
+
+import org.junit.Test;
+
+import static jadx.core.deobf.NameMapper.isValidIdentifier;
+import static jadx.core.deobf.NameMapper.removeInvalidChars;
+import static jadx.core.deobf.NameMapper.removeInvalidCharsMiddle;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
+public class NameMapperTest {
+
+	@Test
+	public void validIdentifiers() {
+		assertThat(isValidIdentifier("ACls"), is(true));
+	}
+
+	@Test
+	public void notValidIdentifiers() {
+		assertThat(isValidIdentifier("1cls"), is(false));
+		assertThat(isValidIdentifier("-cls"), is(false));
+		assertThat(isValidIdentifier("A-cls"), is(false));
+	}
+
+	@Test
+	public void testRemoveInvalidCharsMiddle() {
+		assertThat(removeInvalidCharsMiddle("1cls"), is("1cls"));
+		assertThat(removeInvalidCharsMiddle("-cls"), is("cls"));
+		assertThat(removeInvalidCharsMiddle("A-cls"), is("Acls"));
+	}
+
+	@Test
+	public void testRemoveInvalidChars() {
+		assertThat(removeInvalidChars("1cls", "C"), is("C1cls"));
+		assertThat(removeInvalidChars("-cls", "C"), is("cls"));
+		assertThat(removeInvalidChars("A-cls", "C"), is("Acls"));
+	}
+}