IDEA-156007 'Constant conditions & exceptions' inspection should propagate @Nullable/@NotNull annotations to lambda parameters

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DfaPsiUtil.java

@@ -22,6 +22,7 @@ import com.intellij.codeInspection.dataFlow.instructions.ReturnInstruction;
 import com.intellij.codeInspection.dataFlow.value.DfaValueFactory;
 import com.intellij.lang.java.JavaLanguage;
 import com.intellij.openapi.util.Ref;
+import com.intellij.patterns.PsiJavaPatterns;
 import com.intellij.psi.*;
 import com.intellij.psi.search.LocalSearchScope;
 import com.intellij.psi.search.searches.ReferencesSearch;
@@ -97,6 +98,15 @@ public class DfaPsiUtil {
       return Nullness.NOT_NULL;
     }
 
+    if (PsiJavaPatterns.psiParameter().withParents(PsiParameterList.class, PsiLambdaExpression.class).accepts(owner)) {
+      PsiLambdaExpression lambda = (PsiLambdaExpression)owner.getParent().getParent();
+      int index = lambda.getParameterList().getParameterIndex((PsiParameter)owner);
+      PsiMethod sam = LambdaUtil.getFunctionalInterfaceMethod(lambda.getFunctionalInterfaceType());
+      if (sam != null && index < sam.getParameterList().getParametersCount()) {
+        return getElementNullability(null, sam.getParameterList().getParameters()[index]);
+      }
+    }
+
     return Nullness.UNKNOWN;
   }
 

java/java-tests/testData/inspection/dataFlow/fixture/NotNullLambdaParameter.java

@@ -0,0 +1,14 @@
+import org.jetbrains.annotations.NotNull;
+class Example {
+  interface Listener {
+    void notify(@NotNull String value);
+  }
+
+  public static void main(String[] args) {
+    Listener l = value -> {
+      if (<warning descr="Condition 'value != null' is always 'true'">value != null</warning>) {
+        System.out.println(value);
+      }
+    };
+  }
+}

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspection8Test.java

@@ -47,6 +47,7 @@ public class DataFlowInspection8Test extends DataFlowInspectionTestCase {
   public void testNullableForeachVariable() { doTestWithCustomAnnotations(); }
   public void testOptionalOfNullable() { doTest(); }
   public void testPrimitiveInVoidLambda() { doTest(); }
+  public void testNotNullLambdaParameter() { doTest(); }
 
   public void testNullableArrayComponent() {
     setupCustomAnnotations();