tentative fix for LOGBACK-1713

Signed-off-by: Ceki Gulcu <ceki@qos.ch>

Author: ceki

logback-classic-blackbox/src/test/blackboxInput/joran/conditional/siftNestedWithinIfThen.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE configuration>
+
+<configuration debug="false">
+
+    <if condition='property("HOSTNAME") != null'>
+        <then>
+            <appender name="SIFT" class="ch.qos.logback.classic.sift.SiftingAppender">
+
+                <discriminator>
+                    <key>userid</key>
+                    <defaultValue>ifThenDefault</defaultValue>
+                </discriminator>
+                <sift>
+                    <appender name="list-${userid}"
+                              class="ch.qos.logback.core.read.ListAppender"/>
+                </sift>
+            </appender>
+        </then>
+    </if>
+
+    <root level="DEBUG">
+        <appender-ref ref="SIFT"/>
+    </root>
+
+</configuration>

logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/joran/conditional/ConditionalTest.java

@@ -17,11 +17,14 @@
 import ch.qos.logback.classic.LoggerContext;
 import ch.qos.logback.classic.blackbox.BlackboxClassicTestConstants;
 import ch.qos.logback.classic.joran.JoranConfigurator;
+import ch.qos.logback.classic.sift.SiftingAppender;
 import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
 import ch.qos.logback.core.ConsoleAppender;
 import ch.qos.logback.core.FileAppender;
 import ch.qos.logback.core.joran.spi.JoranException;
 import ch.qos.logback.core.read.ListAppender;
+import ch.qos.logback.core.sift.AppenderTracker;
 import ch.qos.logback.core.status.StatusUtil;
 import ch.qos.logback.core.testUtil.CoreTestConstants;
 import ch.qos.logback.core.testUtil.RandomUtil;
@@ -33,7 +36,9 @@
 import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.util.List;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -43,6 +48,8 @@ public class ConditionalTest {
     LoggerContext context = new LoggerContext();
     Logger root = context.getLogger(Logger.ROOT_LOGGER_NAME);
 
+    Logger logger = context.getLogger(this.getClass().getName());
+
     StatusUtil checker = new StatusUtil(context);
     int diff = RandomUtil.getPositiveInt();
     String randomOutputDir = CoreTestConstants.OUTPUT_DIR_PREFIX + diff + "/";
@@ -142,4 +149,24 @@ public void conditionalInclusionWithInexistentFile() throws JoranException, IOEx
         assertTrue(checker.isErrorFree(0));
     }
 
+    private AppenderTracker<ILoggingEvent> getAppenderTracker() {
+        SiftingAppender ha = (SiftingAppender) root.getAppender("SIFT");
+        return ha.getAppenderTracker();
+    }
+
+    // see also https://jira.qos.ch/browse/LOGBACK-1713
+    @Test
+    public void nestedWithinIfThen() throws JoranException {
+        configure(BlackboxClassicTestConstants.JORAN_INPUT_PREFIX + "conditional/siftNestedWithinIfThen.xml");
+        StatusPrinter.print(context);
+        String msg = "nestedWithinIfThen";
+        logger.debug(msg);
+        Appender<ILoggingEvent> appender = getAppenderTracker().find("ifThenDefault");
+        assertNotNull(appender);
+        ListAppender<ILoggingEvent> listAppender = (ListAppender<ILoggingEvent>) appender;
+        List<ILoggingEvent> eventList = listAppender.list;
+        assertEquals(1, listAppender.list.size());
+        assertEquals(msg, eventList.get(0).getMessage());
+        checker.isWarningOrErrorFree(0);
+    }
 }

logback-core/src/main/java/ch/qos/logback/core/joran/JoranConfiguratorBase.java

@@ -90,7 +90,7 @@ protected void addElementSelectorAndActionAssociations(RuleStore rs) {
         rs.addRule(new ElementSelector("*/if/else"),  ElseAction::new);
         rs.addTransparentPathPart("else");
 
-        rs.addRule(new ElementSelector("configuration/appender/sift"),  SiftAction::new);
+        rs.addRule(new ElementSelector("*/appender/sift"),  SiftAction::new);
         rs.addTransparentPathPart("sift");
 
 

logback-core/src/main/java/ch/qos/logback/core/model/processor/conditional/IfModelHandler.java

@@ -101,6 +101,11 @@ public void handle(ModelInterpretationContext mic, Model model) throws ModelHand
     @Override
     public void postHandle(ModelInterpretationContext mic, Model model) throws ModelHandlerException {
 
+        if(mic.isModelStackEmpty()) {
+            addError("Unexpected unexpected empty model stack.");
+            return;
+        }
+
         Object o = mic.peekModel();
         if (o != ifModel) {
             addWarn("The object [" + o + "] on the top the of the stack is not the expected [" + ifModel);