Build: Add iceberg-bom artifact (apache#8065)

BOMs are pretty useful to align dependencies of a project. Their usage is optional though.

baseline.gradle

@@ -24,6 +24,11 @@ allprojects {
 }
 
 subprojects {
+  if (it.name == 'iceberg-bom') {
+    // the BOM does not build anything, the below plugins are not necessary (and can fail)
+    return
+  }
+
   // Currently, if any subproject applies the blanket Baseline plugin, it forces the Baseline plugin
   // to be applied to ALL projects. And we are not prepared to address all of the build errors that
   // occur as a result at this time. Furthermore, baseline-format will not work out of the box for

build.gradle

@@ -131,6 +131,11 @@ allprojects {
 }
 
 subprojects {
+  if (it.name == 'iceberg-bom') {
+    // the BOM does not build anything, the code below expects "source code"
+    return
+  }
+
   apply plugin: 'java-library'
 
   if (project.name in REVAPI_PROJECTS) {
@@ -1008,3 +1013,41 @@ apply from: 'baseline.gradle'
 apply from: 'deploy.gradle'
 apply from: 'tasks.gradle'
 
+project(':iceberg-bom') {
+  apply plugin: 'java-platform'
+
+  dependencies {
+    constraints {
+      // The Iceberg-Build builds for only one Scala version at a time, so the BOM would also
+      // only contain artifacts for that single Scala version. The following code ensures that
+      // the BOM references the artifacts for all Scala versions.
+      def sparkScalaPattern = ~"(.*)-([0-9][.][0-9]+)_([0-9][.][0-9]+)"
+      def sparkScalaVersions = [
+        "3.3": ["2.12", "2.13"],
+        "3.4": ["2.12", "2.13"],
+        "3.5": ["2.12", "2.13"],
+      ]
+      rootProject.allprojects.forEach {
+        // Do not include ':iceberg-spark', the bom itself and the root project.
+        if (it.name != 'iceberg-bom' && it != rootProject && it.childProjects.isEmpty()) {
+          if (it.name.startsWith("iceberg-spark-")) {
+            def sparkScalaMatcher = sparkScalaPattern.matcher(it.name)
+            if (!sparkScalaMatcher.find()) {
+              throw new GradleException("Expected a Spark/Scala version combination in Gradle project name ${it.name}")
+            }
+            def prjName = sparkScalaMatcher.group(1)
+            def sparkVer = sparkScalaMatcher.group(2)
+            for (def scalaVer in sparkScalaVersions[sparkVer]) {
+              add("api", "${it.group}:$prjName-${sparkVer}_$scalaVer:${it.version}")
+            }
+          } else {
+            add("api", project(it.path))
+          }
+        }
+      }
+    }
+  }
+
+  // Needed to get the "faked" Scala artifacts into the bom
+  javaPlatform { allowDependencies() }
+}

deploy.gradle

@@ -22,62 +22,70 @@ if (project.hasProperty('release') && jdkVersion != '8') {
 }
 
 subprojects {
+  def isBom = it.name == 'iceberg-bom'
+
   apply plugin: 'maven-publish'
   apply plugin: 'signing'
   afterEvaluate {
 
-    task sourceJar(type: Jar, dependsOn: classes) {
-      archiveClassifier.set('sources')
-      from sourceSets.main.allSource
-      group 'build'
-    }
-
-    task javadocJar(type: Jar, dependsOn: javadoc) {
-      archiveClassifier.set('javadoc')
-      from javadoc.destinationDir
-      group 'build'
-    }
+    if (!isBom) {
+      task sourceJar(type: Jar, dependsOn: classes) {
+        archiveClassifier.set('sources')
+        from sourceSets.main.allSource
+        group 'build'
+      }
 
-    task testJar(type: Jar) {
-      archiveClassifier.set('tests')
-      from sourceSets.test.output
-    }
+      task javadocJar(type: Jar, dependsOn: javadoc) {
+        archiveClassifier.set('javadoc')
+        from javadoc.destinationDir
+        group 'build'
+      }
 
-    artifacts {
-      archives sourceJar
-      archives javadocJar
-      archives testJar
-      testArtifacts testJar
-    }
+      task testJar(type: Jar) {
+        archiveClassifier.set('tests')
+        from sourceSets.test.output
+      }
 
-    // add LICENSE and NOTICE
-    [jar, sourceJar, javadocJar, testJar].each { task ->
-      task.dependsOn rootProject.tasks.buildInfo
-      task.from("${rootDir}/build") {
-        include 'iceberg-build.properties'
+      artifacts {
+        archives sourceJar
+        archives javadocJar
+        archives testJar
+        testArtifacts testJar
       }
-      task.from(rootDir) {
-        include 'LICENSE'
-        include 'NOTICE'
+
+      // add LICENSE and NOTICE
+      [jar, sourceJar, javadocJar, testJar].each { task ->
+        task.dependsOn rootProject.tasks.buildInfo
+        task.from("${rootDir}/build") {
+          include 'iceberg-build.properties'
+        }
+        task.from(rootDir) {
+          include 'LICENSE'
+          include 'NOTICE'
+        }
       }
     }
 
     publishing {
       publications {
         apache(MavenPublication) {
-          if (tasks.matching({task -> task.name == 'shadowJar'}).isEmpty()) {
-            from components.java
+          if (isBom) {
+            from components.javaPlatform
           } else {
-            project.shadow.component(it)
-          }
+            if (tasks.matching({task -> task.name == 'shadowJar'}).isEmpty()) {
+              from components.java
+            } else {
+              project.shadow.component(it)
+            }
 
-          artifact sourceJar
-          artifact javadocJar
-          artifact testJar
+            artifact sourceJar
+            artifact javadocJar
+            artifact testJar
 
-          versionMapping {
-            allVariants {
-              fromResolutionResult()
+            versionMapping {
+              allVariants {
+                fromResolutionResult()
+              }
             }
           }
 

settings.gradle

@@ -18,6 +18,7 @@
  */
 
 rootProject.name = 'iceberg'
+include 'bom'
 include 'api'
 include 'common'
 include 'core'
@@ -42,6 +43,7 @@ include 'snowflake'
 include 'delta-lake'
 include 'kafka-connect'
 
+project(':bom').name = 'iceberg-bom'
 project(':api').name = 'iceberg-api'
 project(':common').name = 'iceberg-common'
 project(':core').name = 'iceberg-core'

tasks.gradle

@@ -19,10 +19,11 @@
 
 
 task aggregateJavadoc(type: Javadoc) {
-  dependsOn subprojects.javadoc
-  source subprojects.javadoc.source
+  def javadocTasks = subprojects.findAll { it.name != 'iceberg-bom' }.javadoc
+  dependsOn javadocTasks
+  source javadocTasks.source
   destinationDir project.rootProject.file("site/docs/javadoc/${getJavadocVersion()}")
-  classpath = project.rootProject.files(subprojects.javadoc.classpath)
+  classpath = project.rootProject.files(javadocTasks.classpath)
 
   final JAVADOC_FIX_SEARCH_STR = '\n\n' +
           'getURLPrefix = function(ui) {\n' +