Stream API migration: add narrowing cast if necessary when replacing += with sum()

java/java-impl/src/com/intellij/codeInspection/streamMigration/ReplaceWithSumFix.java

@@ -18,6 +18,8 @@ package com.intellij.codeInspection.streamMigration;
 import com.intellij.codeInspection.streamMigration.StreamApiMigrationInspection.MapOp;
 import com.intellij.openapi.project.Project;
 import com.intellij.psi.*;
+import com.intellij.psi.util.TypeConversionUtil;
+import com.siyeh.ig.psiutils.ParenthesesUtils;
 import org.jetbrains.annotations.NotNull;
 
 /**
@@ -48,6 +50,11 @@ class ReplaceWithSumFix extends MigrateToStreamFix {
     if (!type.equals(PsiType.DOUBLE) && !type.equals(PsiType.LONG)) {
       type = PsiType.INT;
     }
+    PsiType addendType = addend.getType();
+    if(addendType != null && !TypeConversionUtil.isAssignable(type, addendType)) {
+      addend = JavaPsiFacade.getElementFactory(project).createExpressionFromText(
+        "(" + type.getCanonicalText() + ")" + ParenthesesUtils.getText(addend, ParenthesesUtils.MULTIPLICATIVE_PRECEDENCE), addend);
+    }
     StringBuilder builder = generateStream(new MapOp(tb.getLastOperation(), addend, tb.getVariable(), type));
     builder.append(".sum()");
     return replaceWithNumericAddition(project, loopStatement, var, builder, type);

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/afterSumNarrowing.java

@@ -0,0 +1,9 @@
+// "Replace with sum()" "true"
+
+import java.util.Arrays;
+
+public class Main {
+  public void test(long[] list) {
+      int sum = Arrays.stream(list).mapToInt(x -> (int) x).sum();
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/afterSumNarrowingParens.java

@@ -0,0 +1,9 @@
+// "Replace with sum()" "true"
+
+import java.util.Arrays;
+
+public class Main {
+  public void test(double[] list) {
+      int sum = Arrays.stream(list).mapToInt(x -> (int) (x * x)).sum();
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/beforeSumNarrowing.java

@@ -0,0 +1,10 @@
+// "Replace with sum()" "true"
+
+public class Main {
+  public void test(long[] list) {
+    int sum = 0;
+    for(long x : li<caret>st) {
+      sum+=x;
+    }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/beforeSumNarrowingParens.java

@@ -0,0 +1,10 @@
+// "Replace with sum()" "true"
+
+public class Main {
+  public void test(double[] list) {
+    int sum = 0;
+    for(double x : li<caret>st) {
+      sum+=x * x;
+    }
+  }
+}