Tool to generate configuration reference docs

Having documentation about the configuration that is both "up-to-date" and "in-sync with the source code" with the actual code is good practice.

The functionality added in this change allows generating markdown docs from smallrye-config based configuration types, starting at and grouped by types that are annotated with `@ConfigMapping`. The javadoc of the config interfaces and properties is emitted as markdown. On top there is functionality to generate reference docs for "static" types (currently unused in Polaris).

The code is nearly a 1:1 port of the same functionality in Nessie. This change will become useful with/after apache#469.

Gradle projects added in this change are:
* `polaris-config-doc-annotations` adds an annotation used when generating docs to influence the generation of the configuration reference docs.
* `polaris-config-doc-generator` is the reference doc generator implementation, as a "standalone" tool that uses javadoc _infrastructure_. See `ReferenceConfigDocsGenerator` why it needs to be a separate tool than "just" a doclet (class loader isolation issues).
* `polaris-site-reference-docs` actually generates the markdown files from referenced Gradle projects. Currently there are no projects referenced, so generation yields nothing.

The generated docs are not yet integrated into the website, which will happen in a follow-up PR.

Author: snazy

gradle/libs.versions.toml

@@ -21,6 +21,7 @@
 hadoop = "3.4.1"
 iceberg = "1.7.1"
 dropwizard = "4.0.11"
+picocli = "4.7.6"
 slf4j = "2.0.16"
 swagger = "1.6.14"
 
@@ -40,6 +41,7 @@ bouncycastle-bcprov = { module = "org.bouncycastle:bcprov-jdk18on", version = "1
 caffeine = { module = "com.github.ben-manes.caffeine:caffeine", version = "3.1.8" }
 commons-codec1 = { module = "commons-codec:commons-codec", version = "1.17.2" }
 commons-lang3 = { module = "org.apache.commons:commons-lang3", version = "3.17.0" }
+commons-text = { module = "org.apache.commons:commons-text", version = "1.13.0" }
 dropwizard-bom = { module = "io.dropwizard:dropwizard-bom", version.ref = "dropwizard" }
 eclipselink = { module = "org.eclipse.persistence:eclipselink", version = "4.0.5" }
 errorprone = { module = "com.google.errorprone:error_prone_core", version = "2.36.0" }
@@ -67,10 +69,13 @@ micrometer-bom = { module = "io.micrometer:micrometer-bom", version = "1.14.3" }
 mockito-core = { module = "org.mockito:mockito-core", version = "5.15.2" }
 opentelemetry-bom = { module = "io.opentelemetry:opentelemetry-bom", version = "1.46.0" }
 opentelemetry-semconv = { module = "io.opentelemetry.semconv:opentelemetry-semconv", version = "1.25.0-alpha" }
+picocli = { module = "info.picocli:picocli-codegen", version.ref = "picocli" }
+picocli-codegen = { module = "info.picocli:picocli-codegen", version.ref = "picocli" }
 prometheus-metrics-exporter-servlet-jakarta = { module = "io.prometheus:prometheus-metrics-exporter-servlet-jakarta", version = "1.3.5" }
 s3mock-testcontainers = { module = "com.adobe.testing:s3mock-testcontainers", version = "3.12.0" }
 slf4j-api = { module = "org.slf4j:slf4j-api", version.ref = "slf4j" }
 smallrye-common-annotation = { module = "io.smallrye.common:smallrye-common-annotation", version = "2.9.0" }
+smallrye-config-core = { module = "io.smallrye.config:smallrye-config-core", version = "3.10.2" }
 spotbugs-annotations = { module = "com.github.spotbugs:spotbugs-annotations", version = "4.8.6" }
 swagger-annotations = { module = "io.swagger:swagger-annotations", version.ref = "swagger" }
 swagger-jaxrs = { module = "io.swagger:swagger-jaxrs", version.ref = "swagger" }

gradle/projects.main.properties

@@ -29,3 +29,7 @@ polaris-jpa-model=extension/persistence/jpa-model
 polaris-tests=integration-tests
 aggregated-license-report=aggregated-license-report
 polaris-version=tools/version
+
+polaris-ref-config-annotations=tools/ref-config/annotations
+polaris-ref-config-generator=tools/ref-config/generator
+polaris-ref-config-site=tools/ref-config/site

tools/ref-config/annotations/build.gradle.kts

@@ -0,0 +1,25 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+plugins {
+  id("polaris-client")
+  `java-library`
+}
+
+description = "Polaris reference docs annotations"

tools/ref-config/annotations/src/main/java/org/apache/polaris/docs/ConfigDocs.java

@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.polaris.docs;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/** Contains annotations for {@code :polaris-config-doc-generator}. */
+public interface ConfigDocs {
+  /**
+   * For properties-configs, declares a class containing configuration constants for "properties"
+   * and gives it a page name. The generated markdown files will start with this name.
+   */
+  @Target(ElementType.TYPE)
+  @Retention(RetentionPolicy.SOURCE)
+  @interface ConfigPageGroup {
+    String name();
+  }
+
+  /**
+   * Define the "section" in which the config option appears.
+   *
+   * <p>For properties-configs, this declares that a property constant field appears in the
+   * generated markdown files.
+   *
+   * <p>For smallrye-configs, this declares that a property appears under a different "prefix".
+   */
+  @Target({ElementType.FIELD, ElementType.METHOD})
+  @Retention(RetentionPolicy.SOURCE)
+  @interface ConfigItem {
+    /**
+     * The name of the "section" in which this constant field shall appear. The name of the
+     * generated markdown file will "end" with this name.
+     */
+    String section() default "";
+
+    /** For smallrye-configs only: the section docs are taken from property type's javadoc. */
+    boolean sectionDocFromType() default false;
+  }
+
+  /**
+   * For smallrye-configs, gives map-keys a name that appears as a placeholder in the fully
+   * qualified config name in the generated docs.
+   */
+  @Target(ElementType.METHOD)
+  @Retention(RetentionPolicy.SOURCE)
+  @interface ConfigPropertyName {
+    String value() default "";
+  }
+}

tools/ref-config/generator/build.gradle.kts

@@ -0,0 +1,76 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+plugins {
+  id("polaris-server")
+  `java-library`
+  `java-test-fixtures`
+}
+
+description = "Generates Polaris reference docs"
+
+val genTesting by configurations.creating
+
+dependencies {
+  implementation(project(":polaris-ref-config-annotations"))
+
+  implementation(libs.commons.text)
+
+  implementation(libs.smallrye.config.core)
+  implementation(libs.picocli)
+  annotationProcessor(libs.picocli.codegen)
+
+  testFixturesApi(platform(libs.junit.bom))
+  testFixturesApi("org.junit.jupiter:junit-jupiter")
+  testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+  testFixturesApi(libs.assertj.core)
+  testFixturesApi(libs.mockito.core)
+
+  genTesting(project(":polaris-ref-config-annotations"))
+  genTesting(libs.smallrye.config.core)
+}
+
+tasks.named<Test>("test") {
+  // The test needs the classpath for the necessary dependencies (annotations + smallrye-config).
+  // Resolving the dependencies must happen during task execution (not configuration).
+  jvmArgumentProviders.add(
+    CommandLineArgumentProvider {
+      // So, in theory, all 'org.gradle.category' attributes should use the type
+      // org.gradle.api.attributes.Category,
+      // as Category.CATEGORY_ATTRIBUTE is defined. BUT! Some attributes have an attribute type ==
+      // String.class!
+
+      val categoryAttributeAsString = Attribute.of("org.gradle.category", String::class.java)
+
+      val libraries =
+        genTesting.incoming.artifacts
+          .filter { a ->
+            // dependencies:
+            //  org.gradle.category=library
+            val category =
+              a.variant.attributes.getAttribute(Category.CATEGORY_ATTRIBUTE)
+                ?: a.variant.attributes.getAttribute(categoryAttributeAsString)
+            category != null && category.toString() == Category.LIBRARY
+          }
+          .map { a -> a.file }
+
+      listOf("-Dtesting.libraries=" + libraries.joinToString(":"))
+    }
+  )
+}