warn about unused parameter if method is used locally as method reference as it could be transformed to equivalent lambda (IDEA-157988)

java/java-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/PostHighlightingVisitor.java

@@ -406,12 +406,6 @@ class PostHighlightingVisitor {
                                              @NotNull PsiIdentifier identifier,
                                              @NotNull ProgressIndicator progress) {
     if (!myRefCountHolder.isReferenced(parameter) && !UnusedSymbolUtil.isImplicitUsage(myProject, parameter, progress)) {
-      //parameter is defined by functional interface
-      final PsiElement declarationScope = parameter.getDeclarationScope();
-      if (declarationScope instanceof PsiMethod &&
-          myRefCountHolder.isReferencedByMethodReference((PsiMethod)declarationScope, myLanguageLevel)) {
-        return null;
-      }
       String message = JavaErrorMessages.message("parameter.is.not.used", identifier.getText());
       return UnusedSymbolUtil.createUnusedSymbolInfo(identifier, message, myDeadCodeInfoType);
     }

java/java-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/RefCountHolder.java

@@ -222,26 +222,6 @@ class RefCountHolder {
     return usedStatus == Boolean.TRUE;
   }
 
-  boolean isReferencedByMethodReference(@NotNull PsiMethod method, @NotNull LanguageLevel languageLevel) {
-    if (!languageLevel.isAtLeast(LanguageLevel.JDK_1_8)) return false;
-
-    Collection<PsiReference> array;
-    synchronized (myLocalRefsMap) {
-      array = myLocalRefsMap.get(method);
-    }
-
-    if (!array.isEmpty()) {
-      for (PsiReference reference : array) {
-        final PsiElement element = reference.getElement();
-        if (element instanceof PsiMethodReferenceExpression) {
-          return true;
-        }
-      }
-    }
-
-    return false;
-  }
-
   private static boolean isParameterUsedRecursively(@NotNull PsiElement element, @NotNull Collection<PsiReference> array) {
     if (!(element instanceof PsiParameter)) return false;
     PsiParameter parameter = (PsiParameter)element;

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/mostSpecific/BoxingAndOverloadResolution.java

@@ -14,7 +14,7 @@ class Test {
 
 class Test2 {
 
-  static void m(Integer i) { }
+  static void m(Integer <warning descr="Parameter 'i' is never used">i</warning>) { }
 
   interface I1 {
     void m(int x);

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/newMethodRef/AfterDistinctOps.java

@@ -77,7 +77,7 @@ abstract class AbstractCollection<E> implements Collection<E> {
     public boolean add(E e) {
         return true;
     }
-    public boolean addAll(Collection<? extends E> c) {
+    public boolean addAll(Collection<? extends E> <warning descr="Parameter 'c' is never used">c</warning>) {
         boolean modified = false;
         return modified;
     }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/newMethodRef/GenericArrayCreation.java

@@ -6,11 +6,11 @@ class Test {
         Test m(List<Integer> l1, List<Integer> l2);
     }
 
-    static Test meth(List<Integer>... lli) {
+    static Test meth(List<Integer>... <warning descr="Parameter 'lli' is never used">lli</warning>) {
         return null;
     }
 
-    Test(List<Integer>... lli) {}
+    Test(List<Integer>... <warning descr="Parameter 'lli' is never used">lli</warning>) {}
 
     {
         I <warning descr="Variable 'i1' is never used">i1</warning> = <warning descr="Unchecked generics array creation for varargs parameter">Test::meth</warning>;

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/newMethodRef/VarargsParametersCountComparison.java

@@ -1,7 +1,7 @@
 import java.util.stream.Stream;
 
 class A {
-  private void test5(Integer i, String... strings) {}
+  private void test5(Integer <warning descr="Parameter 'i' is never used">i</warning>, String... <warning descr="Parameter 'strings' is never used">strings</warning>) {}
   private void <warning descr="Private method 'test5(java.lang.Integer, java.lang.Integer, java.lang.String...)' is never used">test5</warning>(Integer i, Integer b, String... strings) {
     System.out.println(i);
     System.out.println(b);

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/overloadResolution/IgnoreCandidatesWithLowerApplicabilityLevel.java

@@ -12,7 +12,7 @@ class MyTest<T> {
 
   public static class Builder<E> {
 
-    public Builder<E> add(E element) {
+    public Builder<E> add(E <warning descr="Parameter 'element' is never used">element</warning>) {
       return this;
     }
 

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/overloadResolution/NotPotentiallyCompatibleMethodReference.java

@@ -8,6 +8,6 @@ class Main {
   }
 
   public static boolean checkForJdk(String <warning descr="Parameter 'homePath' is never used">homePath</warning>) {return false;}
-  public static boolean checkForJdk(File homePath) {return false;}
+  public static boolean checkForJdk(File <warning descr="Parameter 'homePath' is never used">homePath</warning>) {return false;}
 
 }