Fix SLF4JLogger.atFatal() returning Level.TRACE instead of Level.FATAL (#4089)

Co-authored-by: Piotr P. Karwasz <pkarwasz-github@apache.org>
Co-authored-by: Volkan Yazıcı <volkan@yazi.ci>

Author: 3 people

log4j-to-slf4j/src/main/java/org/apache/logging/slf4j/SLF4JLogger.java

@@ -363,7 +363,7 @@ public LogBuilder atError() {
 
     @Override
     public LogBuilder atFatal() {
-        return atLevel(Level.TRACE);
+        return atLevel(Level.FATAL);
     }
 
     @Override

log4j-to-slf4j/src/test/java/org/apache/logging/slf4j/LogBuilderTest.java

@@ -103,4 +103,20 @@ void testLevelThreshold(final Consumer<LogBuilder> consumer) {
         assertThat(list.strList).hasSize(1);
         list.strList.clear();
     }
+
+    /**
+     * Verifies that {@code atFatal()} delegates to {@code atLevel(Level.FATAL)}
+     * and not {@code atLevel(Level.TRACE)}.
+     *
+     * @see <a href="https://github.com/apache/logging-log4j2/issues/4068">#4068</a>
+     */
+    @ParameterizedTest
+    @MethodSource("logBuilderMethods")
+    void atFatal_should_log_at_error_level(final Consumer<LogBuilder> consumer) {
+        consumer.accept(logger.atFatal());
+        assertThat(list.strList)
+                .as("atFatal() must produce a log event (SLF4J ERROR equivalent)")
+                .hasSize(1);
+        list.strList.clear();
+    }
 }

src/changelog/.2.x.x/4068_fix_SLF4JLogger_atFatal_wrong_level.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+    <issue id="4068" link="https://github.com/apache/logging-log4j2/issues/4068"/>
+    <issue id="4089" link="https://github.com/apache/logging-log4j2/pull/4089"/>
+    <description format="asciidoc">
+        Fixed `SLF4JLogger.atFatal()` returning `atLevel(Level.TRACE)` instead of `atLevel(Level.FATAL)`, which caused FATAL log events to be silently discarded when using the fluent API through the `log4j-to-slf4j` bridge.
+    </description>
+</entry>