[java] GuardLogStatementRule - fix false negative with lambda

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

@@ -150,7 +150,17 @@ public class GuardLogStatementRule extends AbstractJavaRule implements Rule {
                 return !isConstantStringExpression(child);
             }
         }
-        return false;
+
+        // if there is only one argument and this is a AdditiveExpression, we assume, it is the message
+        // and this is a string concatenation even we are not sure, that the type is string.
+        // this can happen for lambda parameters.
+        return isSingleAdditiveExpression(argumentList);
+    }
+
+    private boolean isSingleAdditiveExpression(ASTArgumentList argumentList) {
+        return argumentList.size() == 1
+                && argumentList.getChild(0).getNumChildren() == 1
+                && argumentList.getChild(0).getChild(0) instanceof ASTAdditiveExpression;
     }
 
     private boolean isConstantStringExpression(JavaNode expr) {

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

@@ -507,12 +507,37 @@ public class Logger {
     private void runTestLambda(TestLambda test) {
         test.apply("one", "two");
     }
+}
+        ]]></code>
+    </test-code>
 
-    public void case6() {
+    <test-code>
+        <description>false negative inside lambdas</description>
+        <expected-problems>2</expected-problems>
+        <expected-linenumbers>19,21</expected-linenumbers>
+        <code><![CDATA[
+public class Logger {
+    private static final Logger LOGGER = new Logger();
+
+    private interface TestLambda {
+        void apply(String arg1, String arg2);
+    }
+    private void runTestLambda(TestLambda test) {
+        test.apply("one", "two");
+    }
+
+    public void case1_no_violation() {
         runTestLambda((String a, String b) -> {
             LOGGER.debug(a);
         });
     }
+
+    public void case2_violation() {
+        runTestLambda((String a, String b) -> {
+            LOGGER.debug(a + b);
+        });
+        runTestLambda((s1, s2) -> {LOGGER.debug(s1 + s2);});
+    }
 }
         ]]></code>
     </test-code>