Implement "Decompile Kotlin to Java" action

Add this action to "Attach sources" notification panel if present
 #KT-11657 Fixed

ChangeLog.md

@@ -213,6 +213,7 @@
 ###### New features
 
 - Added "Decompile" button to Kotlin bytecode toolwindow
+- [`KT-11657`](https://youtrack.jetbrains.com/issue/KT-11657) Allow viewing decompiled Java source code for Kotlin-compiled classes
 - [`KT-11704`](https://youtrack.jetbrains.com/issue/KT-11704) Support file path references inside of Kotlin string literals
 
 ###### Issues fixed:

idea/src/META-INF/plugin.xml

@@ -99,6 +99,11 @@
       <add-to-group group-id="KotlinToolsGroup"/>
     </action>
 
+    <action id="DecompileKotlinToJava" class="org.jetbrains.kotlin.idea.actions.DecompileKotlinToJavaAction"
+            text="Decompile Kotlin To Java">
+      <add-to-group group-id="KotlinToolsGroup"/>
+    </action>
+
     <action id="ExtractFunction" class="org.jetbrains.kotlin.idea.refactoring.introduce.extractFunction.ExtractFunctionAction"
             text="_Function..." use-shortcut-of="ExtractMethod">
       <add-to-group group-id="IntroduceActionsGroup" anchor="after" relative-to-action="ExtractMethod"/>
@@ -600,6 +605,8 @@
     <editorNotificationProvider implementation="org.jetbrains.kotlin.idea.versions.UnsupportedAbiVersionNotificationPanelProvider"/>
     <editorNotificationProvider implementation="org.jetbrains.kotlin.idea.configuration.KotlinSetupEnvironmentNotificationProvider"/>
 
+    <attachSourcesProvider implementation="org.jetbrains.kotlin.idea.actions.DecompileKotlinToJavaActionProvider"/>
+
     <referencesSearch implementation="org.jetbrains.kotlin.idea.search.ideaExtensions.KotlinReferencesSearcher"/>
     <directClassInheritorsSearch implementation="org.jetbrains.kotlin.idea.search.ideaExtensions.KotlinDirectInheritorsSearcher"/>
     <overridingMethodsSearch implementation="org.jetbrains.kotlin.idea.search.ideaExtensions.KotlinOverridingMethodsWithGenericsSearcher"/>

idea/src/org/jetbrains/kotlin/idea/actions/DecompileKotlinToJavaAction.kt

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * 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
+ *
+ * http://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 org.jetbrains.kotlin.idea.actions
+
+import com.intellij.codeInsight.AttachSourcesProvider
+import com.intellij.ide.highlighter.JavaClassFileType
+import com.intellij.openapi.actionSystem.AnAction
+import com.intellij.openapi.actionSystem.AnActionEvent
+import com.intellij.openapi.actionSystem.CommonDataKeys
+import com.intellij.openapi.roots.LibraryOrderEntry
+import com.intellij.openapi.util.ActionCallback
+import com.intellij.psi.PsiFile
+import org.jetbrains.kotlin.idea.internal.showDecompiledCode
+import org.jetbrains.kotlin.psi.KtFile
+
+class DecompileKotlinToJavaAction : AnAction() {
+    override fun actionPerformed(e: AnActionEvent) {
+        val binaryFile = getBinaryKotlinFile(e) ?: return
+
+        showDecompiledCode(binaryFile)
+    }
+
+    override fun update(e: AnActionEvent) {
+        e.presentation.isEnabled = getBinaryKotlinFile(e) != null
+    }
+
+    private fun getBinaryKotlinFile(e: AnActionEvent): KtFile? {
+        val file = e.getData(CommonDataKeys.PSI_FILE) as? KtFile ?: return null
+        if (!file.canBeDecompiledToJava()) return null
+
+        return file
+    }
+
+}
+
+fun KtFile.canBeDecompiledToJava() = isCompiled && virtualFile?.fileType == JavaClassFileType.INSTANCE
+
+// Add action to "Attach sources" notification panel
+class DecompileKotlinToJavaActionProvider() : AttachSourcesProvider {
+    override fun getActions(orderEntries: MutableList<LibraryOrderEntry>, psiFile: PsiFile): Collection<AttachSourcesProvider.AttachSourcesAction> {
+        if (psiFile !is KtFile || !psiFile.canBeDecompiledToJava()) return emptyList()
+
+        return listOf(object : AttachSourcesProvider.AttachSourcesAction {
+            override fun getName() = "Decompile to Java"
+
+            override fun perform(orderEntriesContainingFile: List<LibraryOrderEntry>?): ActionCallback {
+                showDecompiledCode(psiFile)
+                return ActionCallback.DONE
+            }
+
+            override fun getBusyText() = "Kotlin Classfile"
+        })
+    }
+}

idea/src/org/jetbrains/kotlin/idea/internal/KotlinDecompilerAdapter.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.idea.internal
 
 import com.intellij.openapi.fileEditor.OpenFileDescriptor
+import com.intellij.openapi.ui.Messages
 import com.intellij.openapi.util.io.FileUtil
 import com.intellij.openapi.vfs.VfsUtil
 import com.intellij.openapi.vfs.VirtualFile
@@ -29,6 +30,10 @@ import org.jetbrains.kotlin.psi.KtFile
 fun showDecompiledCode(sourceFile: KtFile) {
     val decompilerService = KotlinDecompilerService.getInstance() ?: return
     val decompiledCode = decompilerService.decompile(sourceFile)
+    if (decompiledCode == null) {
+        Messages.showErrorDialog("Cannot decompile ${sourceFile.name}", "Decompiler error")
+        return
+    }
 
     runWriteAction {
         val root = getOrCreateDummyRoot()

idea/src/org/jetbrains/kotlin/idea/internal/KotlinDecompilerService.kt

@@ -20,7 +20,7 @@ import com.intellij.openapi.components.ServiceManager
 import org.jetbrains.kotlin.psi.KtFile
 
 interface KotlinDecompilerService {
-    fun decompile(file: KtFile): String
+    fun decompile(file: KtFile): String?
 
     companion object {
         fun getInstance(): KotlinDecompilerService? {

idea/src/org/jetbrains/kotlin/idea/internal/KotlinDecompilerServiceImpl.kt

@@ -16,30 +16,39 @@
 
 package org.jetbrains.kotlin.idea.internal
 
+import com.intellij.openapi.fileTypes.StdFileTypes
+import com.intellij.openapi.util.io.FileUtil
 import com.intellij.openapi.util.io.FileUtilRt
+import com.intellij.openapi.vfs.VirtualFile
 import org.jetbrains.java.decompiler.IdeaLogger
 import org.jetbrains.java.decompiler.main.decompiler.BaseDecompiler
 import org.jetbrains.java.decompiler.main.extern.IBytecodeProvider
 import org.jetbrains.java.decompiler.main.extern.IFernflowerPreferences
 import org.jetbrains.java.decompiler.main.extern.IResultSaver
+import org.jetbrains.kotlin.idea.actions.canBeDecompiledToJava
 import org.jetbrains.kotlin.psi.KtFile
 import java.io.File
 import java.util.jar.Manifest
 
 class KotlinDecompilerServiceImpl : KotlinDecompilerService {
-    override fun decompile(file: KtFile): String {
-        val generationState = KotlinBytecodeToolWindow.compileSingleFile(file, true, true, true)
+    override fun decompile(file: KtFile): String? {
 
-        val bytecodeMap = hashMapOf<File, ByteArray>()
-        generationState.factory.asList().filter { FileUtilRt.extensionEquals(it.relativePath, "class") }.forEach {
-            bytecodeMap[File("/${it.relativePath}").absoluteFile] = it.asByteArray()
+        val bytecodeMap = when {
+            file.canBeDecompiledToJava() -> bytecodeMapForExistingClassfile(file.virtualFile)
+            !file.isCompiled -> bytecodeMapForSourceFile(file)
+            else -> return null
         }
-
-        val bytecodeProvider = KotlinBytecodeProvider(bytecodeMap)
         val resultSaver = KotlinResultSaver()
         val options = hashMapOf<String, Any>(
-            IFernflowerPreferences.REMOVE_BRIDGE to "0"
+                IFernflowerPreferences.REMOVE_BRIDGE to "0"
         )
+
+        val bytecodeProvider = IBytecodeProvider {
+            externalPath, internalPath ->
+            val path = File(FileUtil.toSystemIndependentName(externalPath))
+            bytecodeMap[path]?.invoke()
+        }
+
         val decompiler = BaseDecompiler(bytecodeProvider, resultSaver, options, IdeaLogger())
         for (path in bytecodeMap.keys) {
             decompiler.addSpace(path, true)
@@ -48,12 +57,29 @@ class KotlinDecompilerServiceImpl : KotlinDecompilerService {
         return resultSaver.resultText
     }
 
-    class KotlinBytecodeProvider(val bytecodeMap: Map<File, ByteArray>) : IBytecodeProvider {
-        override fun getBytecode(externalPath: String?, internalPath: String?): ByteArray? {
-            return bytecodeMap[File(externalPath)]
+    fun bytecodeMapForExistingClassfile(file: VirtualFile): Map<File, () -> ByteArray> {
+        val mask = "${file.nameWithoutExtension}$"
+        val files =
+                mapOf(file.path to file) +
+                file.parent.children.filter {
+                    it.nameWithoutExtension.startsWith(mask) && it.fileType === StdFileTypes.CLASS
+                }.map { it.path to it }
+
+        return files.entries.associate {
+            Pair(File(it.key), { it.value.contentsToByteArray() })
         }
     }
 
+    fun bytecodeMapForSourceFile(file: KtFile): Map<File, () -> ByteArray> {
+        val generationState = KotlinBytecodeToolWindow.compileSingleFile(file, true, true, true)
+
+        val bytecodeMap = hashMapOf<File, () -> ByteArray>()
+        generationState.factory.asList().filter { FileUtilRt.extensionEquals(it.relativePath, "class") }.forEach {
+            bytecodeMap[File("/${it.relativePath}").absoluteFile] = { it.asByteArray() }
+        }
+        return bytecodeMap
+    }
+
     class KotlinResultSaver : IResultSaver {
         private val decompiledText = mutableMapOf<String, String>()