Add support for markdown javadoc

src/net/fabricmc/fernflower/api/FabricJavadocStyle.java

@@ -0,0 +1,12 @@
+package net.fabricmc.fernflower.api;
+
+public enum FabricJavadocStyle {
+  /**
+   * The traditional Javadoc style (default)
+   */
+  HTML,
+  /**
+   * The Markdown Javadoc style introduced in Java 23
+   */
+  MARKDOWN,
+}

src/net/fabricmc/fernflower/api/IFabricJavadocProvider.java

@@ -9,7 +9,7 @@
  * Provides (optional) javadoc for Classes/Methods/Fields encountered by
  *  {@link org.jetbrains.java.decompiler.main.ClassWriter}.
  *
- * May be set as a property in the constructor of {@link org.jetbrains.java.decompiler.main.Fernflower} by using
+ * <p>May be set as a property in the constructor of {@link org.jetbrains.java.decompiler.main.Fernflower} by using
  *  the key {@code IFabricJavadocProvider.PROPERTY_NAME}
  */
 public interface IFabricJavadocProvider {
@@ -20,4 +20,16 @@ public interface IFabricJavadocProvider {
   String getFieldDoc(StructClass structClass, StructField structField);
 
   String getMethodDoc(StructClass structClass, StructMethod structMethod);
+
+  default FabricJavadocStyle getClassJavadocStyle(StructClass structClass) {
+    return FabricJavadocStyle.HTML;
+  }
+
+  default FabricJavadocStyle getFieldJavadocStyle(StructClass structClass, StructField structField) {
+    return getClassJavadocStyle(structClass);
+  }
+
+  default FabricJavadocStyle getMethodJavadocStyle(StructClass structClass, StructMethod structMethod) {
+    return getClassJavadocStyle(structClass);
+  }
 }

src/org/jetbrains/java/decompiler/main/ClassWriter.java

@@ -2,6 +2,8 @@
 package org.jetbrains.java.decompiler.main;
 
 import java.util.concurrent.atomic.AtomicBoolean;
+
+import net.fabricmc.fernflower.api.FabricJavadocStyle;
 import net.fabricmc.fernflower.api.IFabricJavadocProvider;
 import org.jetbrains.java.decompiler.api.plugin.StatementWriter;
 import org.jetbrains.java.decompiler.code.CodeConstants;
@@ -689,7 +691,7 @@ private void writeClassDefinition(ClassNode node, TextBuffer buffer, int indent)
     }
 
     if (javadocProvider != null) {
-      appendJavadoc(buffer, javadocProvider.getClassDoc(cl), indent);
+      appendJavadoc(buffer, javadocProvider.getClassJavadocStyle(cl), javadocProvider.getClassDoc(cl), indent);
     }
 
     appendAnnotations(buffer, indent, cl, -1);
@@ -876,7 +878,7 @@ public void writeField(ClassWrapper wrapper, StructClass cl, StructField fd, Tex
     }
 
     if (javadocProvider != null) {
-      appendJavadoc(buffer, javadocProvider.getFieldDoc(cl, fd), indent);
+      appendJavadoc(buffer, javadocProvider.getFieldJavadocStyle(cl, fd), javadocProvider.getFieldDoc(cl, fd), indent);
     }
     Set<String> writtenAnnotations = appendAnnotations(buffer, indent, fd, TypeAnnotation.FIELD);
 
@@ -1130,7 +1132,7 @@ public boolean writeMethod(ClassNode node, StructMethod mt, int methodIndex, Tex
       }
 
       if (javadocProvider != null) {
-        appendJavadoc(buffer, javadocProvider.getMethodDoc(cl, mt), indent);
+        appendJavadoc(buffer, javadocProvider.getMethodJavadocStyle(cl, mt), javadocProvider.getMethodDoc(cl, mt), indent);
       }
 
       Set<String> writtenAnnotations = appendAnnotations(buffer, indent, mt, TypeAnnotation.METHOD_RETURN_TYPE);
@@ -1786,13 +1788,22 @@ private static void appendComment(TextBuffer buffer, String comment, int indent)
     buffer.appendIndent(indent).append("// $VF: ").append(comment).appendLineSeparator();
   }
 
-  private static void appendJavadoc(TextBuffer buffer, String javaDoc, int indent) {
+  private static void appendJavadoc(TextBuffer buffer, FabricJavadocStyle javadocStyle, String javaDoc, int indent) {
     if (javaDoc == null) return;
-    buffer.appendIndent(indent).append("/**").appendLineSeparator();
-    for (String s : javaDoc.split("\n")) {
-      buffer.appendIndent(indent).append(" * ").append(s).appendLineSeparator();
+    switch (javadocStyle) {
+      case HTML -> {
+        buffer.appendIndent(indent).append("/**").appendLineSeparator();
+        for (String s : javaDoc.split("\n")) {
+          buffer.appendIndent(indent).append(" * ").append(s).appendLineSeparator();
+        }
+        buffer.appendIndent(indent).append(" */").appendLineSeparator();
+      }
+      case MARKDOWN -> {
+        for (String s : javaDoc.split("\n")) {
+          buffer.appendIndent(indent).append("/// ").append(s).appendLineSeparator();
+        }
+      }
     }
-    buffer.appendIndent(indent).append(" */").appendLineSeparator();
   }
 
   public static void appendSyntheticClassComment(StructClass cl, TextBuffer buffer) {

test/org/jetbrains/java/decompiler/SingleClassesTest.java

@@ -1,6 +1,7 @@
 // Copyright 2000-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 package org.jetbrains.java.decompiler;
 
+import net.fabricmc.fernflower.api.FabricJavadocStyle;
 import net.fabricmc.fernflower.api.IFabricJavadocProvider;
 import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences;
 import org.jetbrains.java.decompiler.struct.StructClass;
@@ -98,6 +99,29 @@ public String getMethodDoc(StructClass structClass, StructMethod structMethod) {
         return "Method javadoc for '" + structMethod.getName() + "'";
       }
     });
+    registerSet("Markdown Javadoc", () -> {
+      register(JAVA_8, "TestMarkdownJavadoc");
+    }, IFabricJavadocProvider.PROPERTY_NAME, new IFabricJavadocProvider() {
+      @Override
+      public String getClassDoc(StructClass structClass) {
+        return "Class javadoc for '" + structClass.qualifiedName + "'";
+      }
+
+      @Override
+      public String getFieldDoc(StructClass structClass, StructField structField) {
+        return "Field javadoc for '" + structField.getName() + "'";
+      }
+
+      @Override
+      public String getMethodDoc(StructClass structClass, StructMethod structMethod) {
+        return "Method javadoc for '" + structMethod.getName() + "'";
+      }
+
+      @Override
+      public FabricJavadocStyle getClassJavadocStyle(StructClass structClass) {
+        return FabricJavadocStyle.MARKDOWN;
+      }
+    });
     // TODO: converter renaming different on different platforms?
     registerSet("Renaming", () -> registerFailable(JAVA_8, "TestRenameEntities"),
       IFernflowerPreferences.BYTECODE_SOURCE_MAPPING, "1",

testData/results/pkg/TestMarkdownJavadoc.dec

@@ -0,0 +1,11 @@
+package pkg;
+
+/// Class javadoc for 'pkg/TestMarkdownJavadoc'
+public class TestMarkdownJavadoc {
+   /// Field javadoc for 'field'
+   public int field;
+
+   /// Method javadoc for 'method'
+   public void method() {
+   }
+}

testData/src/java8/pkg/TestMarkdownJavadoc.java

@@ -0,0 +1,9 @@
+package pkg;
+
+public class TestMarkdownJavadoc {
+  public int field;
+
+  public void method() {
+
+  }
+}