Add sub classing interfaces

micrometer-docs-generator/src/main/java/io/micrometer/docs/commons/AbstractSearchingFileVisitor.java

@@ -34,6 +34,7 @@
 import org.jboss.forge.roaster.Roaster;
 import org.jboss.forge.roaster.model.source.EnumConstantSource;
 import org.jboss.forge.roaster.model.source.JavaEnumSource;
+import org.jboss.forge.roaster.model.source.JavaInterfaceSource;
 import org.jboss.forge.roaster.model.source.JavaSource;
 import org.jboss.forge.roaster.model.source.MethodSource;
 
@@ -71,6 +72,20 @@ else if (!path.toString().endsWith(".java")) {
         }
         JavaEnumSource enumSource = (JavaEnumSource) javaSource;
 
+        enumSource.getInterfaces().forEach(interfaceName -> {
+            // Find any interfaces that match our supported interfaces
+            JavaInterfaceSource foundInterface = searchHelper.searchExtendingDocumentationInterfaceName(interfaceName,
+                    this);
+            if (foundInterface != null) {
+                try {
+                    supportedInterfaces().add(Class.forName(interfaceName));
+                }
+                catch (ClassNotFoundException e) {
+                    throw new RuntimeException(e);
+                }
+            }
+        });
+
         if (supportedInterfaces().stream().noneMatch(enumSource::hasInterface)) {
             return FileVisitResult.CONTINUE;
         }

micrometer-docs-generator/src/main/java/io/micrometer/docs/commons/JavaSourceSearchHelper.java

@@ -47,6 +47,7 @@
 import org.jboss.forge.roaster.model.source.EnumConstantSource;
 import org.jboss.forge.roaster.model.source.Import;
 import org.jboss.forge.roaster.model.source.JavaEnumSource;
+import org.jboss.forge.roaster.model.source.JavaInterfaceSource;
 import org.jboss.forge.roaster.model.source.JavaSource;
 import org.jboss.forge.roaster.model.source.MethodHolderSource;
 import org.jboss.forge.roaster.model.source.MethodSource;
@@ -151,6 +152,20 @@ public JavaSource<?> search(String qualifiedName) {
         return info.getJavaSource();
     }
 
+    /**
+     * Search a {@link JavaInterfaceSource} by qualified class name.
+     * @param qualifiedName a qualified class name
+     * @return matched {@link JavaInterfaceSource} or {@code null} if not found.
+     */
+    @Nullable
+    public JavaInterfaceSource searchInterface(String qualifiedName) {
+        JavaSource<?> javaSource = search(qualifiedName);
+        if (javaSource == null || !javaSource.isInterface()) {
+            return null;
+        }
+        return (JavaInterfaceSource) javaSource;
+    }
+
     /**
      * Search the class which is referenced by the enclosing class.
      * @param enclosingJavaSource enclosing java class source
@@ -450,6 +465,61 @@ private JavaSource<?> searchJavaSourceByRoasterTypeName(JavaSource<?> enclosingJ
         return null;
     }
 
+    /**
+     * Search for interfaces that extend the documentation interfaces.
+     * @param interfaceName
+     * @param abstractSearchingFileVisitor
+     * @return the {@link JavaInterfaceSource} that extends the documentation interface or
+     * {@code null} if no matching interface is found
+     */
+    @Nullable
+    public JavaInterfaceSource searchExtendingDocumentationInterfaceName(String interfaceName,
+            AbstractSearchingFileVisitor abstractSearchingFileVisitor) {
+        // delegate to recursive search
+        return searchExtendingDocumentationInterfaceName(interfaceName, new HashSet<>(), abstractSearchingFileVisitor);
+    }
+
+    @Nullable
+    private JavaInterfaceSource searchExtendingDocumentationInterfaceName(String interfaceName, Set<String> visited,
+            AbstractSearchingFileVisitor visitor) {
+        // Search for the interface
+        JavaInterfaceSource interfaceSource = searchInterface(interfaceName);
+        if (interfaceSource == null) {
+            return null;
+        }
+
+        String qualifiedName = interfaceSource.getQualifiedName();
+        logger.trace("Searching ExtendingDocumentationInterface on {} - start", qualifiedName);
+
+        // Cycle detection
+        if (visited.contains(qualifiedName)) {
+            return null;
+        }
+        visited.add(qualifiedName);
+
+        // Check if this interface is supported
+        if (visitor.supportedInterfaces().stream().anyMatch(name -> name.getName().equals(qualifiedName))) {
+            return interfaceSource;
+        }
+
+        // Check all extended interfaces
+        for (String childInterface : interfaceSource.getInterfaces()) {
+            // Check if child is directly supported
+            if (visitor.supportedInterfaces().stream().anyMatch(i -> i.getName().equals(childInterface))) {
+                return interfaceSource;
+            }
+
+            // Recursive search through child
+            JavaInterfaceSource result = searchExtendingDocumentationInterfaceName(childInterface, visited, visitor);
+            if (result != null) {
+                return result;
+            }
+        }
+
+        // No matching interface found
+        return null;
+    }
+
     /**
      * Hierarchically search the implementing name of {@link ObservationConvention} or
      * {@link GlobalObservationConvention}.

micrometer-docs-generator/src/main/java/io/micrometer/docs/metrics/MetricSearchingFileVisitor.java

@@ -56,14 +56,17 @@ class MetricSearchingFileVisitor extends AbstractSearchingFileVisitor {
 
     private final Collection<MetricEntry> entries;
 
+    private final Collection<Class<?>> supportedInterfaces = new ArrayList<>(
+            Arrays.asList(MeterDocumentation.class, ObservationDocumentation.class));
+
     MetricSearchingFileVisitor(Pattern pattern, Collection<MetricEntry> entries, JavaSourceSearchHelper searchHelper) {
         super(pattern, searchHelper);
         this.entries = entries;
     }
 
     @Override
     public Collection<Class<?>> supportedInterfaces() {
-        return Arrays.asList(MeterDocumentation.class, ObservationDocumentation.class);
+        return supportedInterfaces;
     }
 
     @Override

micrometer-docs-generator/src/main/java/io/micrometer/docs/spans/SpanSearchingFileVisitor.java

@@ -56,6 +56,9 @@ class SpanSearchingFileVisitor extends AbstractSearchingFileVisitor {
 
     private final Collection<SpanEntry> spanEntries;
 
+    private final Collection<Class<?>> supportedInterfaces = new ArrayList<>(
+            Arrays.asList(SpanDocumentation.class, ObservationDocumentation.class));
+
     /**
      * The enclosing enum classes for overriding will be excluded from documentation
      */
@@ -68,7 +71,7 @@ class SpanSearchingFileVisitor extends AbstractSearchingFileVisitor {
 
     @Override
     public Collection<Class<?>> supportedInterfaces() {
-        return Arrays.asList(SpanDocumentation.class, ObservationDocumentation.class);
+        return supportedInterfaces;
     }
 
     @Override

micrometer-docs-generator/src/test/java/io/micrometer/docs/metrics/test2/ExtendExtendedMeterDoc.java

@@ -0,0 +1,25 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.metrics.test2;
+
+import java.io.Serializable;
+
+// Added any interface (Serializable) to test if the parser really goes through all extending interfaces
+public interface ExtendExtendedMeterDoc extends Serializable, ExtendMeterDocumentation {
+
+    String secondDescription();
+
+}

micrometer-docs-generator/src/test/java/io/micrometer/docs/metrics/test2/ExtendExtendedMyMetrics.java

@@ -0,0 +1,47 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.metrics.test2;
+
+import io.micrometer.core.instrument.Meter;
+
+public enum ExtendExtendedMyMetrics implements ExtendExtendedMeterDoc {
+
+    /**
+     * Test metric which extends the extended MeterDocumentation interface.
+     */
+    EXTEND_EXTENDED_FOO {
+        @Override
+        public String secondDescription() {
+            return "This comes from ExtendedExtendMeterDoc interface";
+        }
+
+        @Override
+        public String getDescription() {
+            return "This comes from ExtendMeterDocumentation interface";
+        }
+
+        @Override
+        public String getName() {
+            return "extend.extended.foo";
+        }
+
+        @Override
+        public Meter.Type getType() {
+            return Meter.Type.COUNTER;
+        }
+    }
+
+}

micrometer-docs-generator/src/test/java/io/micrometer/docs/metrics/test2/ExtendMeterDocumentation.java

@@ -0,0 +1,28 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.metrics.test2;
+
+import io.micrometer.core.instrument.docs.MeterDocumentation;
+
+public interface ExtendMeterDocumentation extends MeterDocumentation {
+
+    /**
+     * Returns the description (also known as {@code help} in some systems) for the given
+     * meter.
+     */
+    String getDescription();
+
+}

micrometer-docs-generator/src/test/java/io/micrometer/docs/metrics/test2/ExtendedMyMetrics.java

@@ -0,0 +1,42 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.metrics.test2;
+
+import io.micrometer.core.instrument.Meter;
+
+public enum ExtendedMyMetrics implements ExtendMeterDocumentation {
+
+    /**
+     * Test metric which extends the MeterDocumentation interface
+     */
+    FOO {
+        @Override
+        public String getDescription() {
+            return "foo metric";
+        }
+
+        @Override
+        public String getName() {
+            return "extended.foo";
+        }
+
+        @Override
+        public Meter.Type getType() {
+            return Meter.Type.COUNTER;
+        }
+    };
+
+}

micrometer-docs-generator/src/test/java/io/micrometer/docs/metrics/test2/MetricSearchingFileVisitorTest.java

@@ -0,0 +1,45 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.metrics.test2;
+
+import io.micrometer.docs.metrics.MetricsDocGenerator;
+import org.assertj.core.api.BDDAssertions;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.regex.Pattern;
+
+class MetricSearchingFileVisitorTest {
+
+    @Test
+    void should_render_metrics_from_sub_class_interfaces() throws IOException {
+        Path output = Paths.get(".", "build", "_metrics.adoc");
+
+        File sourceRoot = new File(".", "src/test");
+        new MetricsDocGenerator(sourceRoot, Pattern.compile(".*/docs/metrics/test2/[a-zA-Z]+\\.java"),
+                "templates/metrics.adoc.hbs", output)
+            .generate();
+
+        BDDAssertions.then(new String(Files.readAllBytes(output)))
+            .contains("**Metric name** `extended.foo`. **Type** `counter`")
+            .contains("**Metric name** `extend.extended.foo`. **Type** `counter`");
+    }
+
+}

micrometer-docs-generator/src/test/java/io/micrometer/docs/spans/test7/ExtendExtendedMySpan.java

@@ -0,0 +1,40 @@
+/**
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ * https://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 io.micrometer.docs.spans.test7;
+
+public enum ExtendExtendedMySpan implements ExtendExtendedSpanDocumentation {
+
+    /**
+     * Test span for sub-classing documentation interfaces
+     */
+    EXTEND_EXTENDED_FOO {
+        @Override
+        public String secondDescription() {
+            return "This comes from ExtendExtendedSpanDocumentation";
+        }
+
+        @Override
+        public String getDescription() {
+            return "This comes from ExtendSpanDocumentation";
+        }
+
+        @Override
+        public String getName() {
+            return "extend extended foo";
+        }
+    }
+
+}