feat: concat constant strings (#1014)

jadx-core/src/main/java/jadx/core/codegen/TypeGen.java

@@ -1,5 +1,6 @@
 package jadx.core.codegen;
 
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -97,6 +98,43 @@ public class TypeGen {
 		}
 	}
 
+	@Nullable
+	public static String literalToRawString(LiteralArg arg) {
+		ArgType type = arg.getType();
+		if (type == null) {
+			return null;
+		}
+		long lit = arg.getLiteral();
+		switch (type.getPrimitiveType()) {
+			case BOOLEAN:
+				return lit == 0 ? "false" : "true";
+			case CHAR:
+				return String.valueOf((char) lit);
+
+			case BYTE:
+			case SHORT:
+			case INT:
+			case LONG:
+				return Long.toString(lit);
+
+			case FLOAT:
+				return Float.toString(Float.intBitsToFloat((int) lit));
+			case DOUBLE:
+				return Double.toString(Double.longBitsToDouble(lit));
+
+			case OBJECT:
+			case ARRAY:
+				if (lit != 0) {
+					LOG.warn("Wrong object literal: {} for type: {}", lit, type);
+					return Long.toString(lit);
+				}
+				return "null";
+
+			default:
+				return null;
+		}
+	}
+
 	public static String formatShort(long l, boolean cast) {
 		if (l == Short.MAX_VALUE) {
 			return "Short.MAX_VALUE";

jadx-core/src/main/java/jadx/core/dex/instructions/args/InsnArg.java

@@ -232,6 +232,10 @@ public abstract class InsnArg extends Typed {
 		return contains(AFlag.THIS);
 	}
 
+	public boolean isConst() {
+		return isLiteral() || (isInsnWrap() && ((InsnWrapArg) this).getWrapInsn().isConstInsn());
+	}
+
 	protected final <T extends InsnArg> T copyCommonParams(T copy) {
 		copy.copyAttributesFrom(this);
 		copy.setParentInsn(parentInsn);

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

@@ -4,10 +4,12 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
+import org.jetbrains.annotations.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import jadx.core.Consts;
+import jadx.core.codegen.TypeGen;
 import jadx.core.deobf.NameMapper;
 import jadx.core.dex.attributes.AFlag;
 import jadx.core.dex.info.ClassInfo;
@@ -386,7 +388,7 @@ public class SimplifyVisitor extends AbstractVisitor {
 				}
 			}
 			if (!stringArgFound) {
-				// TODO: convert one arg to string using `String.valueOf()`
+				mth.addDebugComment("TODO: convert one arg to string using `String.valueOf()`, args: " + args);
 				return null;
 			}
 
@@ -394,7 +396,8 @@ public class SimplifyVisitor extends AbstractVisitor {
 			removeStringBuilderInsns(mth, toStrInsn, chain);
 
 			List<InsnArg> dupArgs = Utils.collectionMap(args, InsnArg::duplicate);
-			InsnNode concatInsn = new InsnNode(InsnType.STR_CONCAT, dupArgs);
+			List<InsnArg> simplifiedArgs = concatConstArgs(dupArgs);
+			InsnNode concatInsn = new InsnNode(InsnType.STR_CONCAT, simplifiedArgs);
 			concatInsn.setResult(toStrInsn.getResult());
 			concatInsn.add(AFlag.SYNTHETIC);
 			concatInsn.copyAttributesFrom(toStrInsn);
@@ -408,6 +411,67 @@ public class SimplifyVisitor extends AbstractVisitor {
 		return null;
 	}
 
+	private static boolean isConstConcatNeeded(List<InsnArg> args) {
+		boolean prevConst = false;
+		for (InsnArg arg : args) {
+			boolean curConst = arg.isConst();
+			if (curConst && prevConst) {
+				// found 2 consecutive constants
+				return true;
+			}
+			prevConst = curConst;
+		}
+		return false;
+	}
+
+	private static List<InsnArg> concatConstArgs(List<InsnArg> args) {
+		if (!isConstConcatNeeded(args)) {
+			return args;
+		}
+		int size = args.size();
+		List<InsnArg> newArgs = new ArrayList<>(size);
+		List<String> concatList = new ArrayList<>(size);
+		for (int i = 0; i < size; i++) {
+			InsnArg arg = args.get(i);
+			String constStr = getConstString(arg);
+			if (constStr != null) {
+				concatList.add(constStr);
+			} else {
+				if (!concatList.isEmpty()) {
+					newArgs.add(getConcatArg(concatList, args, i));
+					concatList.clear();
+				}
+				newArgs.add(arg);
+			}
+		}
+		if (!concatList.isEmpty()) {
+			newArgs.add(getConcatArg(concatList, args, size));
+		}
+		return newArgs;
+	}
+
+	private static InsnArg getConcatArg(List<String> concatList, List<InsnArg> args, int idx) {
+		if (concatList.size() == 1) {
+			return args.get(idx - 1);
+		}
+		String str = Utils.concatStrings(concatList);
+		return InsnArg.wrapArg(new ConstStringNode(str));
+	}
+
+	@Nullable
+	private static String getConstString(InsnArg arg) {
+		if (arg.isLiteral()) {
+			return TypeGen.literalToRawString((LiteralArg) arg);
+		}
+		if (arg.isInsnWrap()) {
+			InsnNode wrapInsn = ((InsnWrapArg) arg).getWrapInsn();
+			if (wrapInsn instanceof ConstStringNode) {
+				return ((ConstStringNode) wrapInsn).getString();
+			}
+		}
+		return null;
+	}
+
 	/* String concat without assign to variable will cause compilation error */
 	private static void checkResult(MethodNode mth, InsnNode concatInsn) {
 		if (concatInsn.getResult() == null) {

jadx-core/src/main/java/jadx/core/utils/Utils.java

@@ -101,6 +101,18 @@ public class Utils {
 		return sb.toString();
 	}
 
+	public static String concatStrings(List<String> list) {
+		if (isEmpty(list)) {
+			return "";
+		}
+		if (list.size() == 1) {
+			return list.get(0);
+		}
+		StringBuilder sb = new StringBuilder();
+		list.forEach(sb::append);
+		return sb.toString();
+	}
+
 	public static String getStackTrace(Throwable throwable) {
 		if (throwable == null) {
 			return "";