Allow RevApi extensions to be configured via the configuration file

eng/code-quality-reports/pom.xml

@@ -40,6 +40,12 @@
       <version>33.1.0-jre</version> <!-- {x-version-update;com.google.guava:guava;external_dependency} -->
     </dependency>
 
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-databind</artifactId>
+      <version>2.17.2</version> <!-- {x-version-update;com.fasterxml.jackson.core:jackson-databind;external_dependency} -->
+    </dependency>
+
     <dependency>
       <groupId>com.puppycrawl.tools</groupId>
       <artifactId>checkstyle</artifactId>
@@ -65,12 +71,6 @@
       <groupId>org.revapi</groupId>
       <artifactId>revapi</artifactId>
       <version>0.14.4</version> <!-- {x-version-update;org.revapi:revapi;external_dependency} -->
-      <exclusions>
-        <exclusion>
-          <groupId>com.fasterxml.jackson.core</groupId>
-          <artifactId>jackson-databind</artifactId>
-        </exclusion>
-      </exclusions>
     </dependency>
 
     <dependency>

eng/code-quality-reports/src/main/java/com/azure/tools/revapi/transforms/AllowedExternalApis.java

@@ -0,0 +1,81 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.tools.revapi.transforms;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import org.revapi.AnalysisContext;
+import org.revapi.Difference;
+import org.revapi.Element;
+import org.revapi.TransformationResult;
+import org.revapi.base.BaseDifferenceTransform;
+import org.revapi.java.spi.JavaTypeElement;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import javax.lang.model.element.TypeElement;
+import java.util.Collections;
+import java.util.List;
+import java.util.regex.Pattern;
+
+import static com.azure.tools.revapi.transforms.RevApiUtils.createPrefixMatchersFromConfiguration;
+import static com.azure.tools.revapi.transforms.RevApiUtils.findOuterMostClass;
+
+/**
+ * RevApi transformation that allows for ignoring external APIs that are allowed to be exposed.
+ *
+ * @param <E> Type of element to transform.
+ */
+public final class AllowedExternalApis<E extends Element<E>> extends BaseDifferenceTransform<E> {
+    private static final Pattern DIFFERENCE_CODE_PATTERN = Pattern.compile("java.class.externalClassExposedInAPI",
+        Pattern.LITERAL);
+
+    private boolean enabled = false;
+    private List<PrefixMatcher> allowedPrefixes = Collections.emptyList();
+
+    @Override
+    public Pattern[] getDifferenceCodePatterns() {
+        return new Pattern[] { DIFFERENCE_CODE_PATTERN };
+    }
+
+    @Override
+    public TransformationResult tryTransform(@Nullable E oldElement, @Nullable E newElement, Difference difference) {
+        if (!enabled || newElement == null || allowedPrefixes.isEmpty()) {
+            // Missing element to compare.
+            return TransformationResult.keep();
+        }
+
+        if (!(newElement instanceof JavaTypeElement)) {
+            // Unknown element type.
+            return TransformationResult.keep();
+        }
+
+        TypeElement outermostElement = findOuterMostClass(((JavaTypeElement) newElement).getDeclaringElement());
+
+        if (outermostElement == null) {
+            return TransformationResult.keep();
+        }
+
+        String className = outermostElement.getQualifiedName().toString();
+
+        for (PrefixMatcher prefixMatcher : allowedPrefixes) {
+            if (prefixMatcher.test(className)) {
+                return TransformationResult.discard();
+            }
+        }
+
+        return TransformationResult.keep();
+    }
+
+    @Override
+    public String getExtensionId() {
+        return "allowed-external-apis";
+    }
+
+    @Override
+    public void initialize(@Nonnull AnalysisContext analysisContext) {
+        JsonNode enabledNode = analysisContext.getConfigurationNode().get("enabled");
+        this.enabled = enabledNode != null && enabledNode.isBoolean() && enabledNode.booleanValue();
+        this.allowedPrefixes = createPrefixMatchersFromConfiguration(analysisContext, "allowedPrefixes");
+    }
+}