lambda -> method ref: allow pure method call chain (IDEA-164223)

java/java-analysis-impl/src/com/intellij/codeInspection/LambdaCanBeMethodReferenceInspection.java

@@ -17,6 +17,7 @@ package com.intellij.codeInspection;
 
 import com.intellij.codeInsight.FileModificationService;
 import com.intellij.codeInsight.daemon.GroupNames;
+import com.intellij.codeInspection.dataFlow.ControlFlowAnalyzer;
 import com.intellij.codeInspection.ui.MultipleCheckboxOptionsPanel;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.project.Project;
@@ -326,7 +327,13 @@ public class LambdaCanBeMethodReferenceInspection extends BaseJavaBatchLocalInsp
     if (qualifier == null) {
       return true;
     }
-    final Condition<PsiElement> callExpressionCondition = Conditions.instanceOf(PsiCallExpression.class);
+    final Condition<PsiElement> callExpressionCondition = element -> {
+      if (element instanceof PsiCallExpression) {
+        PsiMethod method = ((PsiCallExpression)element).resolveMethod();
+        return !(method != null && ControlFlowAnalyzer.isPure(method));
+      }
+      return false;
+    };
     final Condition<PsiElement> nonFinalFieldRefCondition = expression -> {
       if (expression instanceof PsiReferenceExpression) {
         PsiElement element = ((PsiReferenceExpression)expression).resolve();

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/lambda2methodReference/afterPureMethodCall.java

@@ -0,0 +1,23 @@
+// "Replace lambda with method reference" "true"
+import java.util.*;
+import java.util.function.Predicate;
+
+class Main {
+  public static void main(String[] args) {
+    final Test test = new Test();
+    final List<Sub> subs = Arrays.asList(new Sub(), new Sub());
+
+    subs.forEach(test.getSubs()::add);
+  }
+
+  private static class Test {
+    private final List<Sub> subs = new ArrayList<>();
+
+    private List<Sub> getSubs() {
+      return subs;
+    }
+  }
+
+  private static class Sub {
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/lambda2methodReference/beforePureMethodCall.java

@@ -0,0 +1,23 @@
+// "Replace lambda with method reference" "true"
+import java.util.*;
+import java.util.function.Predicate;
+
+class Main {
+  public static void main(String[] args) {
+    final Test test = new Test();
+    final List<Sub> subs = Arrays.asList(new Sub(), new Sub());
+
+    subs.forEach(t -> test.getSubs().a<caret>dd(t));
+  }
+
+  private static class Test {
+    private final List<Sub> subs = new ArrayList<>();
+
+    private List<Sub> getSubs() {
+      return subs;
+    }
+  }
+
+  private static class Sub {
+  }
+}