Simplify building the default log4j2.properties (#75535)

The process for building `log4j2.properties` in the default distribution
is complicated, expensive and requires all modules and plugins to be
built in order to generate the file. Improve this by directly grabbing
the files and concatenating them.

Also remove code for building the OSS distro config.

distribution/build.gradle

@@ -165,53 +165,32 @@ void copyModule(TaskProvider<Sync> copyTask, Project module) {
   }
 }
 
-// log4j config could be contained in modules, so we must join it together using these tasks
-def buildOssLog4jConfigTaskProvider = tasks.register("buildOssLog4jConfig") {
-  ext.contents = []
-  ext.log4jFile = file("${ossOutputs}/log4j2.properties")
-  outputs.file log4jFile
-}
 def buildDefaultLog4jConfigTaskProvider = tasks.register("buildDefaultLog4jConfig") {
-  dependsOn processDefaultOutputsTaskProvider
-  ext.contents = []
-  ext.log4jFile = file("${defaultOutputs}/log4j2.properties")
-  outputs.file log4jFile
-}
+  mustRunAfter('processDefaultOutputs')
 
-Closure writeLog4jProperties = {
-  def file = file('src/config/log4j2.properties')
-  String mainLog4jProperties = file.getText('UTF-8')
-  it.log4jFile.setText(mainLog4jProperties, 'UTF-8')
-  for (String moduleLog4jProperties : it.contents.reverse()) {
-    it.log4jFile.append(moduleLog4jProperties, 'UTF-8')
+  def outputFile = file("${defaultOutputs}/log4j2.properties")
+  def inputFiles = fileTree('src/config').matching { include 'log4j2.properties' }
+  project(':modules').subprojects.each {
+    inputFiles = inputFiles + it.fileTree('src/main/config').matching { include 'log4j2.properties' }
+  }
+  project(':x-pack:plugin').subprojects.each {
+    inputFiles = inputFiles + it.fileTree('src/main/config').matching { include 'log4j2.properties' }
   }
-}
-buildOssLog4jConfigTaskProvider.configure {
-  doLast(writeLog4jProperties)
-}
-
-buildDefaultLog4jConfigTaskProvider.configure {
-  doLast(writeLog4jProperties)
-}
 
-// copy log4j2.properties from modules that have it
-void copyLog4jProperties(TaskProvider buildTask, Project module) {
-  buildTask.configure {
-    Configuration moduleConfig = moduleZip(module)
+  inputs.files(inputFiles)
+  outputs.file outputFile
 
-    dependsOn moduleConfig
-    doFirst {
-      FileTree tree = zipTree(moduleConfig.singleFile)
-      FileTree filtered = tree.matching {
-        include 'config/log4j2.properties'
-        include '*/config/log4j2.properties' // could be in a bundled plugin
-      }
-      if (filtered.isEmpty() == false) {
-        contents.add('\n\n' + filtered.singleFile.getText('UTF-8'))
+  doLast {
+    outputFile.setText('', 'UTF-8')
+    inputFiles.files.eachWithIndex(
+      { f, i ->
+        if (i != 0) {
+          outputFile.append('\n\n', 'UTF-8')
+        }
+        outputFile.append(f.text, 'UTF-8')
       }
-    }
+    )
   }
-
 }
 
 ext.restTestExpansions = [
@@ -237,9 +216,6 @@ project.rootProject.subprojects.findAll { it.parent.path == ':modules' }.each {
     copyModule(processTransportOutputsTaskProvider, module)
   }
 
-  copyLog4jProperties(buildOssLog4jConfigTaskProvider, module)
-  copyLog4jProperties(buildDefaultLog4jConfigTaskProvider, module)
-
   restTestExpansions['expected.modules.count'] += 1
 }
 
@@ -254,7 +230,6 @@ xpack.subprojects.findAll { it.parent == xpack }.each { Project xpackModule ->
     }
   }
   copyModule(processDefaultOutputsTaskProvider, xpackModule)
-  copyLog4jProperties(buildDefaultLog4jConfigTaskProvider, xpackModule)
 }
 
 copyModule(processSystemdOutputsTaskProvider, project(':modules:systemd'))
@@ -384,12 +359,8 @@ configure(subprojects.findAll { ['archives', 'packages'].contains(it.name) }) {
           exclude 'log4j2.properties' // this is handled separately below
           MavenFilteringHack.filter(it, expansionsForDistribution(distributionType, testDistro, jdk))
         }
-        if (testDistro) {
-          from buildOssLog4jConfigTaskProvider
-        } else {
-          from buildDefaultLog4jConfigTaskProvider
-          from defaultConfigFiles
-        }
+        from buildDefaultLog4jConfigTaskProvider
+        from defaultConfigFiles
       }
     }