[BWC and API enforcement] Introduce checks for enforcing the API restrictions

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>

Author: reta

CHANGELOG.md

@@ -102,6 +102,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add cluster state stats ([#10670](https://github.com/opensearch-project/OpenSearch/pull/10670))
 - Adding slf4j license header to LoggerMessageFormat.java ([#11069](https://github.com/opensearch-project/OpenSearch/pull/11069))
 - [Streaming Indexing] Introduce new experimental server HTTP transport based on Netty 4 and Project Reactor (Reactor Netty) ([#9672](https://github.com/opensearch-project/OpenSearch/pull/9672))
+- [BWC and API enforcement] Introduce checks for enforcing the API restrictions ([#11175](https://github.com/opensearch-project/OpenSearch/pull/11175))
 
 ### Dependencies
 - Bump `com.google.api.grpc:proto-google-common-protos` from 2.10.0 to 2.25.1 ([#10208](https://github.com/opensearch-project/OpenSearch/pull/10208), [#10298](https://github.com/opensearch-project/OpenSearch/pull/10298))

libs/common/src/main/java/org/opensearch/common/annotation/processor/ApiAnnotationProcessor.java

@@ -0,0 +1,352 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.common.annotation.processor;
+
+import org.opensearch.common.Nullable;
+import org.opensearch.common.annotation.DeprecatedApi;
+import org.opensearch.common.annotation.ExperimentalApi;
+import org.opensearch.common.annotation.InternalApi;
+import org.opensearch.common.annotation.PublicApi;
+
+import javax.annotation.processing.AbstractProcessor;
+import javax.annotation.processing.RoundEnvironment;
+import javax.annotation.processing.SupportedAnnotationTypes;
+import javax.lang.model.AnnotatedConstruct;
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.AnnotationMirror;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.Modifier;
+import javax.lang.model.element.PackageElement;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.element.TypeParameterElement;
+import javax.lang.model.element.VariableElement;
+import javax.lang.model.type.ArrayType;
+import javax.lang.model.type.DeclaredType;
+import javax.lang.model.type.ReferenceType;
+import javax.lang.model.type.TypeMirror;
+import javax.lang.model.type.TypeVariable;
+import javax.lang.model.type.WildcardType;
+import javax.tools.Diagnostic.Kind;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * The annotation processor for API related annotations: {@link DeprecatedApi}, {@link ExperimentalApi},
+ * {@link InternalApi} and {@link PublicApi}.
+ * <p>
+ * The checks are built on top of the following rules:
+ * <ul>
+ *  <li>introspect each type annotated with {@link PublicApi}, {@link DeprecatedApi} or {@link ExperimentalApi},
+ *  filtering out package-private declarations</li>
+ *  <li>make sure those leak only {@link PublicApi}, {@link DeprecatedApi} or {@link ExperimentalApi} types as well (exceptions,
+ *    method return values, method arguments, method generic type arguments, class generic type arguments,  annotations)</li>
+ *  <li>recursively follow the type introspection chains to enforce the rules down the line</li>
+ * </ul>
+ */
+@InternalApi
+@SupportedAnnotationTypes("org.opensearch.common.annotation.*")
+public class ApiAnnotationProcessor extends AbstractProcessor {
+    private static final String OPTION_WARN_ON_FAILING_CHECKS = "warnOnFailingChecks";
+    private static final String OPENSEARCH_PACKAGE = "org.opensearch";
+
+    private final Set<Element> reported = new HashSet<>();
+    private final Set<AnnotatedConstruct> processed = new HashSet<>();
+    private Kind reportFailureAs = Kind.ERROR;
+
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+        return SourceVersion.latest();
+    }
+
+    @Override
+    public Set<String> getSupportedOptions() {
+        return Set.of(OPTION_WARN_ON_FAILING_CHECKS);
+    }
+
+    @Override
+    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment round) {
+        processingEnv.getMessager().printMessage(Kind.NOTE, "Processing OpenSearch Api annotations");
+
+        if (processingEnv.getOptions().containsKey(OPTION_WARN_ON_FAILING_CHECKS) == true) {
+            reportFailureAs = Kind.NOTE;
+        }
+
+        final Set<? extends Element> elements = round.getElementsAnnotatedWithAny(
+            Set.of(PublicApi.class, ExperimentalApi.class, DeprecatedApi.class)
+        );
+
+        for (var element : elements) {
+            if (!checkPackage(element)) {
+                continue;
+            }
+
+            // Skip all not-public elements
+            if (!element.getModifiers().contains(Modifier.PUBLIC)) {
+                continue;
+            }
+
+            if (element instanceof TypeElement) {
+                process((TypeElement) element);
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Check top level executable element
+     * @param executable top level executable element
+     */
+    private void process(ExecutableElement executable) {
+        if (!inspectable(executable)) {
+            return;
+        }
+
+        // The executable element should not be internal (unless constructor for injectable core component)
+        checkNotInternal(null, executable);
+
+        // Process method return types
+        final TypeMirror returnType = executable.getReturnType();
+        if (returnType instanceof ReferenceType) {
+            process(executable, (ReferenceType) returnType);
+        }
+
+        // Process method thrown types
+        for (final TypeMirror thrownType : executable.getThrownTypes()) {
+            if (thrownType instanceof ReferenceType) {
+                process(executable, (ReferenceType) thrownType);
+            }
+        }
+
+        // Process method type parameters
+        for (final TypeParameterElement typeParameter : executable.getTypeParameters()) {
+            for (final TypeMirror boundType : typeParameter.getBounds()) {
+                if (boundType instanceof ReferenceType) {
+                    process(executable, (ReferenceType) boundType);
+                }
+            }
+        }
+
+        // Process method arguments
+        for (final VariableElement parameter : executable.getParameters()) {
+            final TypeMirror parameterType = parameter.asType();
+            if (parameterType instanceof ReferenceType) {
+                process(executable, (ReferenceType) parameterType);
+            }
+        }
+    }
+
+    /**
+     * Check wildcard type bounds referred by an element
+     * @param executable element
+     * @param type wildcard type
+     */
+    private void process(ExecutableElement executable, WildcardType type) {
+        if (type.getExtendsBound() instanceof ReferenceType) {
+            process(executable, (ReferenceType) type.getExtendsBound());
+        }
+
+        if (type.getSuperBound() instanceof ReferenceType) {
+            process(executable, (ReferenceType) type.getSuperBound());
+        }
+    }
+
+    /**
+     * Check reference type bounds referred by an executable element
+     * @param executable executable element
+     * @param ref reference type
+     */
+    private void process(ExecutableElement executable, ReferenceType ref) {
+        // The element has been processed already
+        if (processed.add(ref) == false) {
+            return;
+        }
+
+        if (ref instanceof DeclaredType) {
+            final DeclaredType declaredType = (DeclaredType) ref;
+
+            final Element element = declaredType.asElement();
+            if (inspectable(element)) {
+                checkNotInternal(executable.getEnclosingElement(), element);
+                checkPublic(executable.getEnclosingElement(), element);
+            }
+
+            for (final TypeMirror type : declaredType.getTypeArguments()) {
+                if (type instanceof ReferenceType) {
+                    process(executable, (ReferenceType) type);
+                } else if (type instanceof WildcardType) {
+                    process(executable, (WildcardType) type);
+                }
+            }
+        } else if (ref instanceof ArrayType) {
+            final TypeMirror componentType = ((ArrayType) ref).getComponentType();
+            if (componentType instanceof ReferenceType) {
+                process(executable, (ReferenceType) componentType);
+            }
+        } else if (ref instanceof TypeVariable) {
+            final TypeVariable typeVariable = (TypeVariable) ref;
+            if (typeVariable.getUpperBound() instanceof ReferenceType) {
+                process(executable, (ReferenceType) typeVariable.getUpperBound());
+            }
+            if (typeVariable.getLowerBound() instanceof ReferenceType) {
+                process(executable, (ReferenceType) typeVariable.getLowerBound());
+            }
+        }
+
+        // Check this elements annotations
+        for (final AnnotationMirror annotation : ref.getAnnotationMirrors()) {
+            final Element element = annotation.getAnnotationType().asElement();
+            if (inspectable(element)) {
+                checkNotInternal(executable.getEnclosingElement(), element);
+                checkPublic(executable.getEnclosingElement(), element);
+            }
+        }
+    }
+
+    /**
+     * Check if a particular executable element should be inspected or not
+     * @param executable executable element to inspect
+     * @return {@code true} if a particular executable element should be inspected, {@code false} otherwise
+     */
+    private boolean inspectable(ExecutableElement executable) {
+        // The constructors for public APIs could use non-public APIs when those are supposed to be only
+        // consumed (not instantiated) by external consumers.
+        return executable.getKind() != ElementKind.CONSTRUCTOR && executable.getModifiers().contains(Modifier.PUBLIC);
+    }
+
+    /**
+     * Check if a particular element should be inspected or not
+     * @param element element to inspect
+     * @return {@code true} if a particular element should be inspected, {@code false} otherwise
+     */
+    private boolean inspectable(Element element) {
+        final PackageElement pckg = processingEnv.getElementUtils().getPackageOf(element);
+        return pckg.getQualifiedName().toString().startsWith(OPENSEARCH_PACKAGE);
+    }
+
+    /**
+     * Check if a particular element belongs to OpenSeach managed packages
+     * @param element element to inspect
+     * @return {@code true} if a particular element belongs to OpenSeach managed packages, {@code false} otherwise
+     */
+    private boolean checkPackage(Element element) {
+        // The element was reported already
+        if (reported.contains(element)) {
+            return false;
+        }
+
+        final PackageElement pckg = processingEnv.getElementUtils().getPackageOf(element);
+        final boolean belongsToOpenSearch = pckg.getQualifiedName().toString().startsWith(OPENSEARCH_PACKAGE);
+
+        if (!belongsToOpenSearch) {
+            reported.add(element);
+
+            processingEnv.getMessager()
+                .printMessage(
+                    reportFailureAs,
+                    "The type "
+                        + element
+                        + " is not residing in "
+                        + OPENSEARCH_PACKAGE
+                        + ".* package "
+                        + "and should not be annotated as OpenSearch APIs."
+                );
+        }
+
+        return belongsToOpenSearch;
+    }
+
+    /**
+     * Check the fields, methods, constructors, and member types that are directly
+     * declared in this class or interface.
+     * @param type class or interface
+     */
+    private void process(Element type) {
+        // Check the fields, methods, constructors, and member types that are directly
+        // declared in this class or interface.
+        for (final Element element : type.getEnclosedElements()) {
+            // Skip all not-public elements
+            if (!type.getModifiers().contains(Modifier.PUBLIC)) {
+                continue;
+            }
+
+            if (element instanceof ExecutableElement) {
+                process((ExecutableElement) element);
+            }
+        }
+    }
+
+    /**
+     * Check if element is public and annotated with {@link PublicApi}, {@link DeprecatedApi} or {@link ExperimentalApi}
+     * @param referencedBy the referrer for the element
+     * @param element element to check
+     */
+    private void checkPublic(@Nullable Element referencedBy, final Element element) {
+        // The element was reported already
+        if (reported.contains(element)) {
+            return;
+        }
+
+        if (!element.getModifiers().contains(Modifier.PUBLIC)) {
+            reported.add(element);
+
+            processingEnv.getMessager()
+                .printMessage(
+                    reportFailureAs,
+                    "The element "
+                        + element
+                        + " is part of the public APIs but does not have public visibility"
+                        + ((referencedBy != null) ? " (referenced by " + referencedBy + ") " : "")
+                );
+        }
+
+        if (element.getAnnotation(PublicApi.class) == null
+            && element.getAnnotation(ExperimentalApi.class) == null
+            && element.getAnnotation(DeprecatedApi.class) == null) {
+            reported.add(element);
+
+            processingEnv.getMessager()
+                .printMessage(
+                    reportFailureAs,
+                    "The element "
+                        + element
+                        + " is part of the public APIs but is not maked as @PublicApi, @ExperimentalApi or @DeprecatedApi"
+                        + ((referencedBy != null) ? " (referenced by " + referencedBy + ") " : "")
+                );
+        }
+    }
+
+    /**
+     * Check if element is not annotated with {@link InternalApi}
+     * @param referencedBy the referrer for the element
+     * @param element element to check
+     */
+    private void checkNotInternal(@Nullable Element referencedBy, final Element element) {
+        // The element was reported already
+        if (reported.contains(element)) {
+            return;
+        }
+
+        if (element.getAnnotation(InternalApi.class) != null) {
+            reported.add(element);
+
+            processingEnv.getMessager()
+                .printMessage(
+                    reportFailureAs,
+                    "The element "
+                        + element
+                        + " is part of the public APIs but is marked as @InternalApi"
+                        + ((referencedBy != null) ? " (referenced by " + referencedBy + ") " : "")
+                );
+        }
+    }
+}

libs/common/src/main/java/org/opensearch/common/annotation/processor/package-info.java

@@ -0,0 +1,15 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+/**
+ * Classes related yo OpenSearch API annotation processing
+ *
+ * @opensearch.internal
+ */
+@org.opensearch.common.annotation.InternalApi
+package org.opensearch.common.annotation.processor;

libs/common/src/main/resources/META-INF/services/javax.annotation.processing.Processor

@@ -0,0 +1,12 @@
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# The OpenSearch Contributors require contributions made to
+# this file be licensed under the Apache-2.0 license or a
+# compatible open source license.
+#
+# Modifications Copyright OpenSearch Contributors. See
+# GitHub history for details.
+#
+
+org.opensearch.common.annotation.processor.ApiAnnotationProcessor