Don't fail on insufficient parameters in ParameterFormatter (#2337)

log4j-api-test/src/main/java/org/apache/logging/log4j/test/junit/UsingStatusLoggerMock.java

@@ -24,6 +24,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.parallel.ResourceLock;
 
 /**
  * Shortcut to {@link StatusLoggerMockExtension}.
@@ -32,4 +33,5 @@
 @Target({TYPE, METHOD})
 @Documented
 @ExtendWith({ExtensionContextAnchor.class, StatusLoggerMockExtension.class})
+@ResourceLock("log4j2.StatusLogger")
 public @interface UsingStatusLoggerMock {}

log4j-api-test/src/test/java/org/apache/logging/log4j/message/ParameterFormatterTest.java

@@ -17,21 +17,27 @@
 package org.apache.logging.log4j.message;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.verify;
 
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import org.apache.logging.log4j.message.ParameterFormatter.MessagePatternAnalysis;
+import org.apache.logging.log4j.status.StatusLogger;
+import org.apache.logging.log4j.test.junit.UsingStatusLoggerMock;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.CsvSource;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.mockito.ArgumentCaptor;
 
 /**
  * Tests {@link ParameterFormatter}.
  */
-public class ParameterFormatterTest {
+@UsingStatusLoggerMock
+class ParameterFormatterTest {
 
     @ParameterizedTest
     @CsvSource({
@@ -49,7 +55,7 @@ public class ParameterFormatterTest {
         "4,0:2:4:10,false,{}{}{}a{]b{}",
         "5,0:2:4:7:10,false,{}{}{}a{}b{}"
     })
-    public void test_pattern_analysis(
+    void test_pattern_analysis(
             final int placeholderCount,
             final String placeholderCharIndicesString,
             final boolean escapedPlaceholderFound,
@@ -65,9 +71,24 @@ public void test_pattern_analysis(
         }
     }
 
+    @ParameterizedTest
+    @CsvSource({"1,foo {}", "2,bar {}{}"})
+    void insufficient_args_should_not_throw_an_exception(final int placeholderCount, final String pattern) {
+        final int argCount = placeholderCount - 1;
+        final String formattedPattern = ParameterFormatter.format(pattern, new Object[argCount], argCount);
+        assertThat(formattedPattern).isEqualTo(pattern);
+        final ArgumentCaptor<Throwable> errorCaptor = ArgumentCaptor.forClass(Throwable.class);
+        verify(StatusLogger.getLogger()).error(eq("parameter formatting failure"), errorCaptor.capture());
+        final Throwable error = errorCaptor.getValue();
+        assertThat(error)
+                .hasMessage(
+                        "found %d argument placeholders, but provided %d for pattern `%s`",
+                        placeholderCount, argCount, pattern);
+    }
+
     @ParameterizedTest
     @MethodSource("messageFormattingTestCases")
-    void assertMessageFormatting(
+    void test_message_formatting(
             final String pattern, final Object[] args, final int argCount, final String expectedFormattedMessage) {
         MessagePatternAnalysis analysis = ParameterFormatter.analyzePattern(pattern, -1);
         final StringBuilder buffer = new StringBuilder();

log4j-api/src/main/java/org/apache/logging/log4j/message/ParameterFormatter.java

@@ -26,6 +26,8 @@
 import java.util.IdentityHashMap;
 import java.util.Map;
 import java.util.Set;
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.status.StatusLogger;
 import org.apache.logging.log4j.util.StringBuilders;
 
 /**
@@ -62,6 +64,8 @@ final class ParameterFormatter {
     private static final char DELIM_STOP = '}';
     private static final char ESCAPE_CHAR = '\\';
 
+    private static final Logger STATUS_LOGGER = StatusLogger.getLogger();
+
     private static final DateTimeFormatter DATE_FORMATTER =
             DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ").withZone(ZoneId.systemDefault());
 
@@ -236,7 +240,10 @@ static void formatMessage(
             final String message = String.format(
                     "found %d argument placeholders, but provided %d for pattern `%s`",
                     analysis.placeholderCount, args.length, pattern);
-            throw new IllegalArgumentException(message);
+            final Throwable error = new IllegalArgumentException(message);
+            STATUS_LOGGER.error("parameter formatting failure", error);
+            buffer.append(pattern);
+            return;
         }
 
         // Fast-path for patterns containing no escapes
@@ -250,7 +257,7 @@ static void formatMessage(
         }
     }
 
-    static void formatMessageContainingNoEscapes(
+    private static void formatMessageContainingNoEscapes(
             final StringBuilder buffer,
             final String pattern,
             final Object[] args,
@@ -271,7 +278,7 @@ static void formatMessageContainingNoEscapes(
         buffer.append(pattern, precedingTextStartIndex, pattern.length());
     }
 
-    static void formatMessageContainingEscapes(
+    private static void formatMessageContainingEscapes(
             final StringBuilder buffer,
             final String pattern,
             final Object[] args,

src/changelog/.2.x.x/fix_ParameterFormatter_for_insufficient_args.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="http://logging.apache.org/log4j/changelog"
+       xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.3.xsd"
+       type="fixed">
+  <description format="asciidoc">Fix that parameterized message formatting doesn't throw an exception when there are insufficient number of parameters</description>
+</entry>