dfa: consider methods in @Immutable classes referentially transparent (IDEA-167658)

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/value/DfaExpressionFactory.java

@@ -15,6 +15,7 @@
  */
 package com.intellij.codeInspection.dataFlow.value;
 
+import com.intellij.codeInsight.AnnotationUtil;
 import com.intellij.codeInspection.dataFlow.DfaPsiUtil;
 import com.intellij.codeInspection.dataFlow.Nullness;
 import com.intellij.openapi.diagnostic.Logger;
@@ -173,6 +174,9 @@ public class DfaExpressionFactory {
           return method;
         }
       }
+      if (AnnotationUtil.findAnnotation(method.getContainingClass(), "javax.annotation.concurrent.Immutable") != null) {
+        return method;
+      }
     }
     return null;
   }

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

@@ -0,0 +1,13 @@
+@javax.annotation.concurrent.Immutable
+interface Intf {
+  @org.jetbrains.annotations.Nullable String foo();
+}
+
+class Usage {
+  void bar(Intf i) {
+    if (i.foo() != null) {
+      System.out.println(i.foo().length());
+    }
+  }
+
+}

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

@@ -260,6 +260,11 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
   public void testFinalGetter() { doTest(); }
   public void testGetterResultsNotSame() { doTest(); }
 
+  public void testImmutableClassNonGetterMethod() {
+    myFixture.addClass("package javax.annotation.concurrent; public @interface Immutable {}");
+    doTest();
+  }
+
   public void testByteBufferGetter() {
     myFixture.addClass("package java.nio; public class MappedByteBuffer { public int getInt() {} }");
     doTest();