Fix behavior for #3160

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/ASTArrayInitializer.java

@@ -34,6 +34,13 @@ public final class ASTArrayInitializer extends AbstractJavaExpr implements ASTEx
         return visitor.visit(this, data);
     }
 
+    /**
+     * Return the number of elements.
+     */
+    public int length() {
+        return getNumChildren();
+    }
+
 
     @Override
     public Iterator<ASTExpression> iterator() {

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/bestpractices/MethodReturnsInternalArrayRule.java

@@ -4,10 +4,16 @@
 
 package net.sourceforge.pmd.lang.java.rule.bestpractices;
 
+import net.sourceforge.pmd.lang.ast.NodeStream;
+import net.sourceforge.pmd.lang.java.ast.ASTArrayAllocation;
+import net.sourceforge.pmd.lang.java.ast.ASTArrayDimExpr;
+import net.sourceforge.pmd.lang.java.ast.ASTArrayInitializer;
+import net.sourceforge.pmd.lang.java.ast.ASTArrayTypeDim;
 import net.sourceforge.pmd.lang.java.ast.ASTAssignableExpr.ASTNamedReferenceExpr;
 import net.sourceforge.pmd.lang.java.ast.ASTExpression;
 import net.sourceforge.pmd.lang.java.ast.ASTMethodDeclaration;
 import net.sourceforge.pmd.lang.java.ast.ASTReturnStatement;
+import net.sourceforge.pmd.lang.java.ast.ASTVariableDeclaratorId;
 import net.sourceforge.pmd.lang.java.ast.AccessNode.Visibility;
 import net.sourceforge.pmd.lang.java.rule.AbstractJavaRulechainRule;
 import net.sourceforge.pmd.lang.java.rule.internal.JavaRuleUtil;
@@ -43,7 +49,7 @@ public class MethodReturnsInternalArrayRule extends AbstractJavaRulechainRule {
                     JVariableSymbol symbol = reference.getReferencedSym();
                     if (symbol instanceof JFieldSymbol) {
                         JFieldSymbol field = (JFieldSymbol) symbol;
-                        if (field.isStatic() && !field.isFinal()) {
+                        if (field.isStatic() && (!field.isFinal() || !hasZeroLengthArrayInitializer(field))) {
                             addViolation(data, returnStmt, reference.getName());
                         }
                     }
@@ -52,4 +58,31 @@ public class MethodReturnsInternalArrayRule extends AbstractJavaRulechainRule {
         }
         return data;
     }
+
+    private static boolean hasZeroLengthArrayInitializer(JFieldSymbol sym) {
+        return NodeStream.of(sym.tryGetNode())
+                         .map(ASTVariableDeclaratorId::getInitializer)
+                         .filter(MethodReturnsInternalArrayRule::isZeroLengthArrayExpr)
+                         .nonEmpty();
+    }
+
+    private static boolean isZeroLengthArrayExpr(ASTExpression expr) {
+        if (expr instanceof ASTArrayInitializer) {
+            // {}
+            return ((ASTArrayInitializer) expr).length() == 0;
+        } else if (expr instanceof ASTArrayAllocation) {
+            ASTArrayInitializer init = ((ASTArrayAllocation) expr).getArrayInitializer();
+            if (init != null) {
+                // new int[] {}
+                return init.length() == 0;
+            } else {
+                // new int[0]
+                ASTArrayTypeDim lastChild = ((ASTArrayAllocation) expr).getTypeNode().getDimensions().getLastChild();
+                if (lastChild instanceof ASTArrayDimExpr) {
+                    return JavaRuleUtil.isIntLit(((ASTArrayDimExpr) lastChild).getLengthExpression(), 0);
+                }
+            }
+        }
+        return false;
+    }
 }

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/JavaRuleUtil.java

@@ -123,9 +123,12 @@ public final class JavaRuleUtil {
         return false;
     }
 
-    private static boolean isIntLit(JavaNode e, int value) {
+    /**
+     * Return true if the number is an int or long literal with the given int value.
+     */
+    public static boolean isIntLit(JavaNode e, int value) {
         if (e instanceof ASTNumericLiteral) {
-            return ((ASTNumericLiteral) e).getValueAsInt() == value;
+            return ((ASTNumericLiteral) e).isIntegral() && ((ASTNumericLiteral) e).getValueAsInt() == value;
         }
         return false;
     }

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/MethodReturnsInternalArray.xml

@@ -402,8 +402,8 @@ public class OuterClass {
 
     <test-code>
         <description>Detect returned static arrays</description>
-        <expected-problems>1</expected-problems>
-        <expected-linenumbers>16</expected-linenumbers>
+        <expected-problems>2</expected-problems>
+        <expected-linenumbers>8,16</expected-linenumbers>
         <code><![CDATA[
 import java.util.concurrent.Callable;
 
@@ -412,7 +412,7 @@ public class MyClass {
     private final Callable<String[]> returnsFooBar = new Callable<String[]>() {
         @Override
         public String[] call() {
-            return FOO_BAR; // no violation, because FOO_BAR is final. See https://sourceforge.net/p/pmd/bugs/1475/
+            return FOO_BAR;
         }
     };