Support dumping stats for number of generated sources by annotation processors

^KT-51132 In Progress

plugins/kapt3/kapt3-base/src/org/jetbrains/kotlin/kapt3/base/annotationProcessing.kt

@@ -152,6 +152,10 @@ private fun dumpProcessorTiming(wrappedProcessors: List<ProcessorWrapper>, apRep
         wrappedProcessors.forEach { processor ->
             appendLine(processor.renderSpentTime())
         }
+        appendLine("Generated files report:")
+        wrappedProcessors.forEach { processor ->
+            appendLine(processor.renderGenerations())
+        }
     })
 }
 
@@ -182,12 +186,14 @@ private fun reportIfRunningNonIncrementally(
 private class ProcessorWrapper(private val delegate: IncrementalProcessor) : Processor by delegate {
     private var initTime: Long = 0
     private val roundTime = mutableListOf<Long>()
+    private val sourcesGenerated = mutableListOf<Int>()
 
     override fun process(annotations: MutableSet<out TypeElement>, roundEnv: RoundEnvironment): Boolean {
         val (time, result) = measureTimeMillisWithResult {
             delegate.process(annotations, roundEnv)
         }
 
+        updateGenerationStats(roundEnv)
         roundTime += time
         return result
     }
@@ -225,6 +231,38 @@ private class ProcessorWrapper(private val delegate: IncrementalProcessor) : Pro
                 "init: $initTime ms, " +
                 "${roundTime.size} round(s): ${roundTime.joinToString { "$it ms" }}"
     }
+
+    fun renderGenerations(): String {
+        val processorName = delegate.processorName
+
+        return "$processorName: " +
+                "total sources: ${sourcesGenerated.sum()}, " +
+                "sources per round: ${sourcesGenerated.joinToString()}"
+    }
+
+    private fun updateGenerationStats(roundEnv: RoundEnvironment) {
+        var numSourcesGenerated = -1
+        try {
+            val procEnv = roundEnv::class.java.getDeclaredField("processingEnv")
+            procEnv.isAccessible = true
+            val proEnvObj = procEnv.get(roundEnv) as ProcessingEnvironment
+
+            val filerField = JavacProcessingEnvironment::class.java.getDeclaredField("filer")
+            filerField.isAccessible = true
+            val filerObj = filerField.get(proEnvObj)
+
+            val genSourceNameField = JavacFiler::class.java.getDeclaredField("generatedSourceNames")
+            genSourceNameField.isAccessible = true
+            val genSourceNameObj = genSourceNameField.get(filerObj)
+
+            @Suppress("UNCHECKED_CAST")
+            val sources: Set<String>? = genSourceNameObj as? Set<String>
+            numSourcesGenerated = sources?.size ?: -1
+        } catch (e: Exception) {
+            // Not much we can do
+        }
+        sourcesGenerated.add(numSourcesGenerated)
+    }
 }
 
 fun KaptContext.parseJavaFiles(javaSourceFiles: List<File>): JavacList<JCTree.JCCompilationUnit> {