Detect external vararg methods too (if available on the classpath)

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

@@ -0,0 +1,70 @@
+package org.jetbrains.java.decompiler.modules.decompiler;
+
+import org.jetbrains.java.decompiler.struct.gen.MethodDescriptor;
+import org.jetbrains.java.decompiler.struct.gen.VarType;
+
+import java.lang.reflect.Method;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+public class ClasspathHelper {
+
+  private static final Map<String, Method> METHOD_CACHE = Collections.synchronizedMap(new HashMap<>());
+
+  public static Method findMethod(String classname, String methodName, MethodDescriptor descriptor) {
+    String targetClass = classname.replace('/', '.');
+    String methodSignature = buildMethodSignature(targetClass + '.' + methodName, descriptor);
+
+    Method method;
+    if (METHOD_CACHE.containsKey(methodSignature)) {
+      method = METHOD_CACHE.get(methodSignature);
+    }
+    else {
+      method = findMethodOnClasspath(targetClass, methodSignature);
+      METHOD_CACHE.put(methodSignature, method);
+    }
+
+    return method;
+  }
+
+  private static Method findMethodOnClasspath(String targetClass, String methodSignature) {
+    try {
+      Class cls = Class.forName(targetClass);
+      for (Method mtd : cls.getMethods()) {
+        // use contains() to ignore access modifiers and thrown exceptions
+        if (mtd.toString().contains(methodSignature)) {
+          return mtd;
+        }
+      }
+    }
+    catch (Exception e) {
+      // ignore
+    }
+    return null;
+  }
+
+  private static String buildMethodSignature(String name, MethodDescriptor md) {
+    StringBuilder sb = new StringBuilder();
+
+    appendType(sb, md.ret);
+    sb.append(' ').append(name).append('(');
+    for (VarType param : md.params) {
+      appendType(sb, param);
+      sb.append(',');
+    }
+    if (sb.charAt(sb.length() - 1) == ',') {
+      sb.setLength(sb.length() - 1);
+    }
+    sb.append(')');
+
+    return sb.toString();
+  }
+
+  private static void appendType(StringBuilder sb, VarType type) {
+    sb.append(type.value.replace('/', '.'));
+    for (int i = 0; i < type.arrayDim; i++) {
+      sb.append("[]");
+    }
+  }
+}

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

@@ -22,6 +22,7 @@ import org.jetbrains.java.decompiler.main.TextBuffer;
 import org.jetbrains.java.decompiler.main.collectors.BytecodeMappingTracer;
 import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences;
 import org.jetbrains.java.decompiler.main.rels.MethodWrapper;
+import org.jetbrains.java.decompiler.modules.decompiler.ClasspathHelper;
 import org.jetbrains.java.decompiler.modules.decompiler.ExprProcessor;
 import org.jetbrains.java.decompiler.modules.decompiler.vars.CheckTypesResult;
 import org.jetbrains.java.decompiler.modules.decompiler.vars.VarProcessor;
@@ -39,6 +40,7 @@ import org.jetbrains.java.decompiler.util.InterpreterUtil;
 import org.jetbrains.java.decompiler.util.ListStack;
 import org.jetbrains.java.decompiler.util.TextUtil;
 
+import java.lang.reflect.Method;
 import java.util.*;
 import java.util.Map.Entry;
 
@@ -392,7 +394,9 @@ public class InvocationExprent extends Exprent {
       }
     }
     else {
-      // TODO: try to check the class on the classpath
+      // try to check the class on the classpath
+      Method mtd = ClasspathHelper.findMethod(classname, name, descriptor);
+      return mtd != null && mtd.isVarArgs();
     }
     return false;
   }

testData/results/TestClassLambda.dec

@@ -15,7 +15,7 @@ public class TestClassLambda {
    public int field = 0;
 
    public void testLambda() {
-      List var1 = Arrays.asList(new Integer[]{Integer.valueOf(1), Integer.valueOf(2), Integer.valueOf(3), Integer.valueOf(4), Integer.valueOf(5), Integer.valueOf(6), Integer.valueOf(7)});// 29
+      List var1 = Arrays.asList(Integer.valueOf(1), Integer.valueOf(2), Integer.valueOf(3), Integer.valueOf(4), Integer.valueOf(5), Integer.valueOf(6), Integer.valueOf(7));// 29
       int var2 = (int)Math.random();// 30
       var1.forEach((var2x) -> {// 32
          int var3 = 2 * var2x.intValue();// 33

testData/results/TestVarArgCalls.dec

@@ -8,11 +8,11 @@ public class TestVarArgCalls {
       this.printComplex("Test");// 9
       this.printComplex("Test: %[0]s", new String[]{"abc"});// 10
       this.printComplex("Test: %[0]s - %[0]s", new String[]{"abc"}, new String[]{"DEF"});// 11
-      String.format("Test", new Object[0]);// 13
+      String.format("Test");// 13
-      String.format("Test: %d", new Object[]{Integer.valueOf(123)});// 14
+      String.format("Test: %d", Integer.valueOf(123));// 14
-      String.format("Test: %d - %s", new Object[]{Integer.valueOf(123), "DEF"});// 15
+      String.format("Test: %d - %s", Integer.valueOf(123), "DEF");// 15
       Object[] data = new Object[]{"Hello"};// 17
-      String.format("Test: %s", new Object[]{data});// 18
+      String.format("Test: %s", (Object)data);// 18
       String.format("Test: %s", (Object[])data);// 19
    }// 20
 
@@ -46,7 +46,6 @@ class 'pkg/TestVarArgCalls' {
       68      9
       6c      9
       6f      10
-      71      10
       75      10
       79      11
       81      11