fixed lambda parameter names already used in the context

src/org/jetbrains/java/decompiler/main/collectors/VarNamesCollector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 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.
@@ -15,6 +15,7 @@
  */
 package org.jetbrains.java.decompiler.main.collectors;
 
+import java.util.Collection;
 import java.util.HashSet;
 import java.util.Set;
 
@@ -24,7 +25,7 @@ public class VarNamesCollector {
 
   public VarNamesCollector() { }
 
-  public VarNamesCollector(Set<String> setNames) {
+  public VarNamesCollector(Collection<String> setNames) {
     usedNames.addAll(setNames);
   }
 

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

@@ -142,19 +142,25 @@ public class NestedClassProcessor {
           if (expr.type == Exprent.EXPRENT_NEW) {
             NewExprent new_expr = (NewExprent)expr;
 
+            VarNamesCollector enclosingCollector = new VarNamesCollector(enclosingMethod.varproc.getVarNames());
+
             if (new_expr.isLambda() && lambda_class_type.equals(new_expr.getNewType())) {
               InvocationExprent inv_dynamic = new_expr.getConstructor();
 
               int param_index = is_static_lambda_content ? 0 : 1;
               int varIndex = is_static_lambda_content ? 0 : 1;
 
-              for (int i = 0; i < vars_count; ++i) {
+              for (int i = 0; i < md_content.params.length; ++i) {
+                VarVersionPair varVersion = new VarVersionPair(varIndex, 0);
+                if (i < vars_count) {
                   Exprent param = inv_dynamic.getLstParameters().get(param_index + i);
 
                   if (param.type == Exprent.EXPRENT_VAR) {
-                  VarVersionPair pair = new VarVersionPair((VarExprent)param);
-                  String name = enclosingMethod.varproc.getVarName(pair);
-                  mapNewNames.put(new VarVersionPair(varIndex, 0), name);
+                    mapNewNames.put(varVersion, enclosingMethod.varproc.getVarName(new VarVersionPair((VarExprent)param)));
+                  }
+                }
+                else {
+                  mapNewNames.put(varVersion, enclosingCollector.getFreeName(method.varproc.getVarName(varVersion)));
                 }
 
                 varIndex += md_content.params[i].stackSize;

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

@@ -115,6 +115,10 @@ public class VarProcessor {
     mapVarNames.put(pair, name);
   }
 
+  public Collection<String> getVarNames() {
+    return mapVarNames != null ? mapVarNames.values() : Collections.emptySet();
+  }
+
   public int getVarFinal(VarVersionPair pair) {
     return varVersions == null ? VarTypeProcessor.VAR_FINAL : varVersions.getVarFinal(pair);
   }

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

@@ -110,6 +110,7 @@ public class SingleClassesTest {
   @Test public void testSwitchOnEnum() { doTest("pkg/TestSwitchOnEnum");}
   //@Test public void TestSwitchOnStrings() { doTest("pkg/TestSwitchOnStrings");}
   @Test public void testVarArgCalls() { doTest("pkg/TestVarArgCalls"); }
+  @Test public void testLambdaParams() { doTest("pkg/TestLambdaParams"); }
 
   private void doTest(String testFile, String... companionFiles) {
     ConsoleDecompiler decompiler = fixture.getDecompiler();

testData/results/TestLambdaParams.dec

@@ -0,0 +1,48 @@
+package pkg;
+
+import java.util.function.Function;
+
+public class TestLambdaParams {
+   public static void toCollection(Object var0) {
+      Object var1 = null;// 23
+      Function var2 = (var1x) -> {
+         return var0;
+      };// 24
+      Function var3 = (var1x) -> {
+         return var1;
+      };// 25
+      Function var4 = (var0x) -> {
+         return var0x;
+      };// 26
+   }// 27
+}
+
+class 'pkg/TestLambdaParams' {
+   method 'lambda$toCollection$0 (Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;' {
+      1      8
+   }
+
+   method 'lambda$toCollection$1 (Ljava/lang/Class;Ljava/lang/Object;)Ljava/lang/Object;' {
+      1      11
+   }
+
+   method 'lambda$toCollection$2 (Ljava/lang/Object;)Ljava/lang/Object;' {
+      1      14
+   }
+
+   method 'toCollection (Ljava/lang/Object;)V' {
+      0      6
+      1      6
+      8      9
+      f      12
+      15      15
+      17      16
+   }
+}
+
+Lines mapping:
+23 <-> 7
+24 <-> 10
+25 <-> 13
+26 <-> 16
+27 <-> 17

testData/src/pkg/TestLambdaParams.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2000-2014 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.util.function.BinaryOperator;
+import java.util.function.Function;
+
+public class TestLambdaParams {
+  public static void toCollection(Object collectionFactory) {
+    Class a = null;
+    Function f = r1 -> collectionFactory;
+    Function f1 = r1 -> a;
+    Function f2 = r1 -> r1;
+  }
+}