improve codegen in simple case

java/java-impl/src/com/intellij/codeInspection/streamMigration/FindExtremumMigration.java

@@ -243,6 +243,13 @@ class FindExtremumMigration extends BaseStreamApiMigration {
                                      boolean isNegated);
   }
 
+  @NotNull
+  private static String getLambdaText(PsiExpression loopVarExpression, TerminalBlock terminalBlock) {
+    return ExpressionUtils.isReferenceTo(loopVarExpression, terminalBlock.getVariable())
+           ? CommonClassNames.JAVA_UTIL_COMPARATOR + ".naturalOrder()"
+           : LambdaUtil.createLambda(terminalBlock.getVariable(), loopVarExpression);
+  }
+
   //Person maxPerson = null;
   //int maxAge = 0;
   //for (Person person : personList) {
@@ -294,7 +301,7 @@ class FindExtremumMigration extends BaseStreamApiMigration {
       TerminalBlock blockWithFilter =
         myTerminalBlock.add(new StreamApiMigrationInspection.FilterOp(condition, myTerminalBlock.getVariable(), false));
 
-      String lambdaText = LambdaUtil.createLambda(myTerminalBlock.getVariable(), myExtremumKeyExpr);
+      String lambdaText = getLambdaText(myExtremumKeyExpr, myTerminalBlock);
       String comparator;
       if(myComparator == null) {
         comparator = CommonClassNames.JAVA_UTIL_COMPARATOR + "." + method + "(" + lambdaText + ")";
@@ -561,7 +568,7 @@ class FindExtremumMigration extends BaseStreamApiMigration {
       if(myComparator == null) {
         String method = getComparingMethod(loopVarExpressionType);
         if (method == null) return null;
-        String lambdaText = LambdaUtil.createLambda(myTerminalBlock.getVariable(), myLoopVarExpression);
+        String lambdaText = getLambdaText(myLoopVarExpression, myTerminalBlock);
         comparator = CommonClassNames.JAVA_UTIL_COMPARATOR + "." + method + "(" + lambdaText + ")";
       } else {
         String comparatorName = myComparator.getName();

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/minMax/afterMinReferenceNaturalOrder.java

@@ -0,0 +1,34 @@
+// "Replace with min()" "true"
+
+import java.util.*;
+
+public class Main {
+  static class Person implements Comparable<Person> {
+    String name;
+    int age;
+
+    public String getName() {
+      return name;
+    }
+
+    public int getAge() {
+      return age;
+    }
+
+    public Person(String name, int age) {
+      this.name = name;
+      this.age = age;
+    }
+  }
+
+  public Person work() {
+    List<Person> personList = Arrays.asList(
+      new Person("Roman", 21),
+      new Person("James", 25),
+      new Person("Kelly", 12)
+    );
+      Person minPerson = personList.stream().filter(p -> p.getAge() > 13).min(Comparator.comparing(Comparator.naturalOrder())).orElse(null);
+
+      return minPerson;
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/minMax/beforeMinReferenceNaturalOrder.java

@@ -0,0 +1,41 @@
+// "Replace with min()" "true"
+
+import java.util.*;
+
+public class Main {
+  static class Person implements Comparable<Person> {
+    String name;
+    int age;
+
+    public String getName() {
+      return name;
+    }
+
+    public int getAge() {
+      return age;
+    }
+
+    public Person(String name, int age) {
+      this.name = name;
+      this.age = age;
+    }
+  }
+
+  public Person work() {
+    List<Person> personList = Arrays.asList(
+      new Person("Roman", 21),
+      new Person("James", 25),
+      new Person("Kelly", 12)
+    );
+    Person minPerson = null;
+    for <caret>(Person p : personList) {
+      if(p.getAge() > 13) {
+        if (minPerson == null || minPerson.compareTo(p) > 0) {
+          minPerson = p;
+        }
+      }
+    }
+
+    return minPerson;
+  }
+}