From 0c1ca54543811fefcb19cd8d9f37c7caca1abbba Mon Sep 17 00:00:00 2001
From: "Piotr P. Karwasz" <piotr.github@karwasz.org>
Date: Mon, 30 Sep 2024 17:10:42 +0200
Subject: [PATCH] Remove `log4j-core` dependency from SLF4J bridges

To prepare for the migration between Log4j Core 2 and Log4j Core 3 this PR removes the runtime dependency on `log4j-core` from both `log4j-slf4j-impl` and `log4j-slf4j2-impl`.

This explicitly reverts the changes in
[LOG4J2-3601](https://issues.apache.org/jira/browse/LOG4J2-3601)
---
 log4j-slf4j-impl/pom.xml                      | 42 +++++++++++------
 log4j-slf4j2-impl/pom.xml                     | 20 ++++++--
 src/changelog/.2.x.x/.release-notes.adoc.ftl  | 47 ++++++++++++++++++-
 .../.2.x.x/slf4j_impl_remove_log4j_core.xml   |  9 ++++
 4 files changed, 98 insertions(+), 20 deletions(-)
 create mode 100644 src/changelog/.2.x.x/slf4j_impl_remove_log4j_core.xml

diff --git a/log4j-slf4j-impl/pom.xml b/log4j-slf4j-impl/pom.xml
index 32d129b150c..4e391249722 100644
--- a/log4j-slf4j-impl/pom.xml
+++ b/log4j-slf4j-impl/pom.xml
@@ -49,71 +49,83 @@
   </dependencyManagement>
 
   <dependencies>
+
     <dependency>
       <groupId>org.osgi</groupId>
       <artifactId>org.osgi.core</artifactId>
       <scope>provided</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-api</artifactId>
     </dependency>
+
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
-      <artifactId>log4j-core</artifactId>
-      <scope>runtime</scope>
+      <artifactId>log4j-api-test</artifactId>
+      <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
-      <artifactId>log4j-api-test</artifactId>
+      <artifactId>log4j-core</artifactId>
       <scope>test</scope>
-      <exclusions>
-        <exclusion>
-          <groupId>org.slf4j</groupId>
-          <artifactId>slf4j-api</artifactId>
-        </exclusion>
-      </exclusions>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-core-test</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-to-slf4j</artifactId>
       <scope>test</scope>
-      <exclusions>
-        <exclusion>
-          <groupId>org.slf4j</groupId>
-          <artifactId>slf4j-api</artifactId>
-        </exclusion>
-      </exclusions>
     </dependency>
+
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-csv</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-lang3</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-engine</artifactId>
       <scope>test</scope>
     </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-params</artifactId>
+      <scope>test</scope>
+    </dependency>
+
     <dependency>
       <groupId>org.junit.vintage</groupId>
       <artifactId>junit-vintage-engine</artifactId>
       <scope>test</scope>
     </dependency>
+
   </dependencies>
   <build>
     <plugins>
diff --git a/log4j-slf4j2-impl/pom.xml b/log4j-slf4j2-impl/pom.xml
index 20fcad9700b..c6947a81ba4 100644
--- a/log4j-slf4j2-impl/pom.xml
+++ b/log4j-slf4j2-impl/pom.xml
@@ -50,69 +50,83 @@
   </dependencyManagement>
 
   <dependencies>
+
     <dependency>
       <groupId>org.osgi</groupId>
       <artifactId>org.osgi.core</artifactId>
       <scope>provided</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-api</artifactId>
     </dependency>
+
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-api</artifactId>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
-      <artifactId>log4j-core</artifactId>
-      <scope>runtime</scope>
+      <artifactId>log4j-api-test</artifactId>
+      <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
-      <artifactId>log4j-api-test</artifactId>
+      <artifactId>log4j-core</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-core-test</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-to-slf4j</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.assertj</groupId>
       <artifactId>assertj-core</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-csv</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-lang3</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-engine</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-params</artifactId>
       <scope>test</scope>
     </dependency>
+
     <dependency>
       <groupId>org.junit.vintage</groupId>
       <artifactId>junit-vintage-engine</artifactId>
       <scope>test</scope>
     </dependency>
+
   </dependencies>
   <build>
     <plugins>
diff --git a/src/changelog/.2.x.x/.release-notes.adoc.ftl b/src/changelog/.2.x.x/.release-notes.adoc.ftl
index 319c60da1d9..a72161243f3 100644
--- a/src/changelog/.2.x.x/.release-notes.adoc.ftl
+++ b/src/changelog/.2.x.x/.release-notes.adoc.ftl
@@ -22,8 +22,51 @@
 
 This releases contains ...
 
-=== JMX changes
+=== SLF4J implementations (bridges)
 
-Starting in version 2.24.0, JMX support is disabled by default and can be re-enabled via the `log4j2.disableJmx=false` system property.
+To prepare for the migration between Log4j Core 2 and Log4j Core 3, the
+xref:components.adoc#log4j-slf4j-impl[`log4j-slf4j-impl`]
+and
+xref:components.adoc#log4j-slf4j-impl[`log4j-slf4j2-impl`]
+bridges between SLF4J and Log4j API, no longer depend on Log4j Core 2.
+Users should specify the logging implementation of their choice explicitly in their dependency manager:
+
+[tabs]
+====
+Maven::
++
+We assume you use xref:components.adoc#log4j-bom[`log4j-bom`] for dependency management.
++
+[source,xml]
+----
+<!-- Bridge from SLF4J 2 to Log4j API -->
+<dependency>
+  <groupId>org.apache.logging.log4j</groupId>
+  <artifactId>log4j-slf4j2-impl</artifactId>
+  <scope>runtime</scope>
+</dependency>
+
+<!-- Log4j API implementation -->
+<dependency>
+  <groupId>org.apache.logging.log4j</groupId>
+  <artifactId>log4j-core</artifactId>
+  <scope>runtime</scope>
+</dependency>
+----
+
+Gradle::
++
+We assume you use xref:components.adoc#log4j-bom[`log4j-bom`] for dependency management.
++
+[source,groovy]
+----
+// Bridge from SLF4J 2 to Log4j API
+runtimeOnly 'org.apache.logging.log4j:log4j-slf4j2-impl'
+// Log4j API implementation
+runtimeOnly 'org.apache.logging.log4j:log4j-core'
+----
+====
+
+See xref:manual/installation.adoc#impl-core[Installing Log4j Core] for more details.
 
 <#include "../.changelog.adoc.ftl">
diff --git a/src/changelog/.2.x.x/slf4j_impl_remove_log4j_core.xml b/src/changelog/.2.x.x/slf4j_impl_remove_log4j_core.xml
new file mode 100644
index 00000000000..15c2dd8967f
--- /dev/null
+++ b/src/changelog/.2.x.x/slf4j_impl_remove_log4j_core.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="changed">
+  <description format="asciidoc">Removes Log4j Core from the runtime dependencies of `log4j-slf4j-impl` and
+    `log4j-slf4j2-impl`
+  </description>
+</entry>