feat(plugins-api): Generate a JSON representation of the plugin spec

Generate a JSON representation of the plugin spec which can be used as
input for other tools, for example, to generate documentation.

Signed-off-by: Martin Nonnenmacher <martin.nonnenmacher@bosch.com>

plugins/api/src/main/kotlin/JsonSpecGenerator.kt

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2024 The ORT Project Authors (see <https://github.com/oss-review-toolkit/ort/blob/main/NOTICE>)
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * License-Filename: LICENSE
+ */
+
+package org.ossreviewtoolkit.plugins.api
+
+import com.google.devtools.ksp.processing.CodeGenerator
+import com.google.devtools.ksp.processing.Dependencies
+
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.addJsonObject
+import kotlinx.serialization.json.buildJsonObject
+import kotlinx.serialization.json.encodeToStream
+import kotlinx.serialization.json.put
+import kotlinx.serialization.json.putJsonArray
+import kotlinx.serialization.json.putJsonObject
+
+class JsonSpecGenerator(private val codeGenerator: CodeGenerator) {
+    private val json = Json {
+        prettyPrint = true
+    }
+
+    @OptIn(ExperimentalSerializationApi::class)
+    fun generate(pluginSpec: PluginSpec) {
+        val jsonObject = buildJsonObject {
+            putJsonObject("descriptor") {
+                put("name", pluginSpec.descriptor.name)
+                put("className", pluginSpec.descriptor.className)
+                put("description", pluginSpec.descriptor.description)
+
+                putJsonArray("options") {
+                    pluginSpec.descriptor.options.forEach {
+                        addJsonObject {
+                            put("name", it.name)
+                            put("type", it.type.name)
+                            put("description", it.description)
+                            put("default", it.defaultValue)
+                            put("isRequired", it.isRequired)
+                        }
+                    }
+                }
+            }
+
+            put("configClass", pluginSpec.configClass?.typeName.toString())
+            put("factoryClass", pluginSpec.factory.qualifiedName)
+        }
+
+        codeGenerator.createNewFileByPath(
+            dependencies = Dependencies(aggregating = true, *listOfNotNull(pluginSpec.containingFile).toTypedArray()),
+            path = "META-INF/plugin/${pluginSpec.packageName}.${pluginSpec.descriptor.className}",
+            extensionName = "json"
+        ).use { output ->
+            json.encodeToStream(jsonObject, output)
+        }
+    }
+}

plugins/api/src/main/kotlin/PluginProcessor.kt

@@ -37,6 +37,7 @@ class PluginProcessor(codeGenerator: CodeGenerator) : SymbolProcessor {
 
     private val specFactory = PluginSpecFactory()
     private val factoryGenerator = PluginFactoryGenerator(codeGenerator)
+    private val jsonGenerator = JsonSpecGenerator(codeGenerator)
 
     /**
      * Process all classes annotated with [OrtPlugin] to generate plugin factories for them.
@@ -66,6 +67,7 @@ class PluginProcessor(codeGenerator: CodeGenerator) : SymbolProcessor {
 
             val pluginSpec = specFactory.create(pluginAnnotation, pluginClass, pluginFactoryClass)
             factoryGenerator.generate(pluginSpec)
+            jsonGenerator.generate(pluginSpec)
         }
 
         invoked = true