LambdaUtil#isIdentityLambda

java/java-impl/src/com/intellij/codeInspection/RedundantStreamOptionalCallInspection.java

@@ -183,12 +183,12 @@ public class RedundantStreamOptionalCallInspection extends BaseJavaBatchLocalIns
     }
     if (expression instanceof PsiLambdaExpression) {
       PsiLambdaExpression lambda = (PsiLambdaExpression)expression;
+      if (LambdaUtil.isIdentityLambda(lambda)) return true;
+      if (!allowBoxUnbox) return false;
       PsiExpression body = LambdaUtil.extractSingleExpressionFromBody(lambda.getBody());
       PsiParameter[] parameters = lambda.getParameterList().getParameters();
       if (parameters.length != 1) return false;
       PsiParameter parameter = parameters[0];
-      if (ExpressionUtils.isReferenceTo(body, parameter)) return true;
-      if (!allowBoxUnbox) return false;
       PsiMethodCallExpression call = tryCast(PsiUtil.skipParenthesizedExprDown(body), PsiMethodCallExpression.class);
       if (call == null) return false;
       PsiReferenceExpression methodExpression = call.getMethodExpression();

java/java-impl/src/com/intellij/codeInspection/SimplifyStreamApiCallChainsInspection.java

@@ -410,13 +410,7 @@ public class SimplifyStreamApiCallChainsInspection extends BaseJavaBatchLocalIns
                                                           "valueOf", PsiType.BOOLEAN)) {
       return true;
     }
-    if (arg instanceof PsiLambdaExpression) {
-      PsiLambdaExpression lambda = (PsiLambdaExpression)arg;
-      PsiExpression body = LambdaUtil.extractSingleExpressionFromBody(lambda.getBody());
-      PsiParameterList parameters = lambda.getParameterList();
-      return parameters.getParametersCount() == 1 && ExpressionUtils.isReferenceTo(body, parameters.getParameters()[0]);
-    }
-    return false;
+    return arg instanceof PsiLambdaExpression && LambdaUtil.isIdentityLambda((PsiLambdaExpression)arg);
   }
 
   @Nullable

java/java-psi-api/src/com/intellij/psi/LambdaUtil.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2016 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.
@@ -931,6 +931,30 @@ public class LambdaUtil {
     return variable.getName() + " -> " + expression.getText();
   }
 
+  /**
+   * Returns true if lambda has single parameter and its return value is the same as parameter.
+   *
+   * <p>
+   * The lambdas like this are considered identity lambda: {@code x -> x}, {@code x -> {return x;}}
+   * {@code (String x) -> (x)}, etc.</p>
+   *
+   * <p>
+   * This method does not check the lambda type, also it does not check whether auto-(un)boxing occurs,
+   * so a lambda like {@code ((Predicate<Boolean>)b -> b)} is also identity lambda even though it performs
+   * auto-unboxing.
+   * </p>
+   *
+   * @param lambda a lambda to check
+   * @return true if the supplied lambda is an identity lambda
+   */
+  public static boolean isIdentityLambda(PsiLambdaExpression lambda) {
+    PsiParameterList parameters = lambda.getParameterList();
+    if(parameters.getParametersCount() != 1) return false;
+    PsiExpression expression = PsiUtil.skipParenthesizedExprDown(extractSingleExpressionFromBody(lambda.getBody()));
+    return expression instanceof PsiReferenceExpression &&
+           ((PsiReferenceExpression)expression).isReferenceTo(parameters.getParameters()[0]);
+  }
+
   public static class TypeParamsChecker extends PsiTypeVisitor<Boolean> {
     private PsiMethod myMethod;
     private final PsiClass myClass;