Add internal intellij plugin (#1248)

This introduces an IntelliJ plugin that's meant to assist with development of the Pkl codebase itself.

The plugin adds a file editor that opens snippet tests in a split editor pane, showing the input on the left side and output on the right side.

pkl-internal-intellij-plugin/src/main/kotlin/org/pkl/internal/intellij/SnippetTestEditorProvider.kt

@@ -0,0 +1,76 @@
+/*
+ * Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * 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 org.pkl.internal.intellij
+
+import com.intellij.openapi.fileEditor.*
+import com.intellij.openapi.fileEditor.impl.text.TextEditorProvider
+import com.intellij.openapi.project.DumbAware
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.openapi.vfs.VirtualFileManager
+
+class SnippetTestEditorProvider : FileEditorProvider, DumbAware {
+
+  private val hiddenExtensionRegex = Regex(".*[.]([^.]*)[.]pkl")
+
+  override fun accept(project: Project, file: VirtualFile): Boolean {
+    return isSnippetTestInputFile(file) && findOutputFile(file) != null
+  }
+
+  override fun createEditor(project: Project, file: VirtualFile): FileEditor {
+    val textEditorProvider = TextEditorProvider.getInstance()
+    val outputFile = findOutputFile(file) ?: return textEditorProvider.createEditor(project, file)
+
+    val inputEditor = textEditorProvider.createEditor(project, file) as TextEditor
+    val outputEditor = textEditorProvider.createEditor(project, outputFile) as TextEditor
+
+    return SnippetTestSplitEditor(inputEditor, outputEditor)
+  }
+
+  override fun getEditorTypeId(): String = "snippet-test-split-editor"
+
+  override fun getPolicy(): FileEditorPolicy = FileEditorPolicy.HIDE_DEFAULT_EDITOR
+
+  private fun isSnippetTestInputFile(file: VirtualFile): Boolean {
+    val path = file.path
+    return path.contains("/src/test/files/") && path.contains("/input/") && file.extension == "pkl"
+  }
+
+  private fun possibleOutputPaths(testType: String, relativePath: String): String? {
+    return when (testType) {
+      "LanguageSnippetTests" ->
+        if (relativePath.matches(hiddenExtensionRegex)) relativePath.dropLast(4)
+        else relativePath.dropLast(3) + "pcf"
+      "FormatterSnippetTests" -> relativePath
+      "SnippetTests" -> relativePath.replaceAfterLast('.', "yaml")
+      else -> null
+    }
+  }
+
+  private fun findOutputFile(inputFile: VirtualFile): VirtualFile? {
+    val path = inputFile.path
+    val inputPattern = Regex(".*/src/test/files/(\\w+)/input/(.+)$")
+    val match = inputPattern.find(path) ?: return null
+
+    val testType = match.groupValues[1]
+    val relativePath = match.groupValues[2]
+    val relativeOutputPath = possibleOutputPaths(testType, relativePath) ?: return null
+    val outputPath = path.replace("/input/$relativePath", "/output/$relativeOutputPath")
+    val fileManager = VirtualFileManager.getInstance()
+    return fileManager.findFileByUrl("file://$outputPath")
+      ?: fileManager.findFileByUrl("file://${outputPath.replaceAfterLast('.', "err")}")
+  }
+}

pkl-internal-intellij-plugin/src/main/kotlin/org/pkl/internal/intellij/SnippetTestSplitEditor.kt

@@ -0,0 +1,165 @@
+/*
+ * Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * 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 org.pkl.internal.intellij
+
+import com.intellij.icons.AllIcons
+import com.intellij.openapi.actionSystem.*
+import com.intellij.openapi.fileEditor.FileEditor
+import com.intellij.openapi.fileEditor.FileEditorLocation
+import com.intellij.openapi.fileEditor.FileEditorState
+import com.intellij.openapi.fileEditor.FileEditorStateLevel
+import com.intellij.openapi.fileEditor.TextEditor
+import com.intellij.openapi.util.UserDataHolderBase
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.ui.components.JBPanel
+import java.awt.BorderLayout
+import java.beans.PropertyChangeListener
+import javax.swing.JComponent
+import javax.swing.JSplitPane
+
+class SnippetTestSplitEditor(
+  private val inputEditor: TextEditor,
+  private val outputEditor: TextEditor,
+) : UserDataHolderBase(), FileEditor {
+
+  private var currentViewMode = ViewMode.SPLIT
+
+  private val splitPane: JSplitPane =
+    JSplitPane(JSplitPane.HORIZONTAL_SPLIT, inputEditor.component, outputEditor.component).apply {
+      resizeWeight = 0.5
+    }
+
+  private val mainPanel =
+    JBPanel<JBPanel<*>>(BorderLayout()).apply {
+      add(createToolbar(), BorderLayout.NORTH)
+      add(splitPane, BorderLayout.CENTER)
+    }
+
+  private fun createToolbar(): JComponent {
+    val actionGroup =
+      DefaultActionGroup().apply {
+        add(ShowInputOnlyAction())
+        add(ShowSplitAction())
+      }
+
+    val toolbar =
+      ActionManager.getInstance().createActionToolbar("SnippetTestEditor", actionGroup, true)
+    toolbar.targetComponent = mainPanel
+    return toolbar.component
+  }
+
+  private fun setViewMode(mode: ViewMode) {
+    if (currentViewMode == mode) return
+    currentViewMode = mode
+
+    // Remove the current center component
+    val layout = mainPanel.layout as BorderLayout
+    layout.getLayoutComponent(BorderLayout.CENTER)?.let { mainPanel.remove(it) }
+
+    when (mode) {
+      ViewMode.INPUT_ONLY -> {
+        mainPanel.add(inputEditor.component, BorderLayout.CENTER)
+      }
+      ViewMode.SPLIT -> {
+        // Re-add components to splitPane in case they were removed
+        splitPane.leftComponent = inputEditor.component
+        splitPane.rightComponent = outputEditor.component
+        mainPanel.add(splitPane, BorderLayout.CENTER)
+      }
+    }
+
+    mainPanel.revalidate()
+    mainPanel.repaint()
+  }
+
+  override fun getComponent(): JComponent = mainPanel
+
+  override fun getPreferredFocusedComponent(): JComponent? = inputEditor.preferredFocusedComponent
+
+  override fun getName(): String = "Snippet Test"
+
+  override fun getFile(): VirtualFile? = inputEditor.file
+
+  override fun setState(state: FileEditorState) {
+    if (state is SnippetTestSplitEditorState) {
+      inputEditor.setState(state.inputState)
+      outputEditor.setState(state.outputState)
+    }
+  }
+
+  override fun getState(level: FileEditorStateLevel): FileEditorState {
+    return SnippetTestSplitEditorState(inputEditor.getState(level), outputEditor.getState(level))
+  }
+
+  override fun isModified(): Boolean = inputEditor.isModified || outputEditor.isModified
+
+  override fun isValid(): Boolean = inputEditor.isValid && outputEditor.isValid
+
+  override fun addPropertyChangeListener(listener: PropertyChangeListener) {
+    inputEditor.addPropertyChangeListener(listener)
+    outputEditor.addPropertyChangeListener(listener)
+  }
+
+  override fun removePropertyChangeListener(listener: PropertyChangeListener) {
+    inputEditor.removePropertyChangeListener(listener)
+    outputEditor.removePropertyChangeListener(listener)
+  }
+
+  override fun getCurrentLocation(): FileEditorLocation? = inputEditor.currentLocation
+
+  override fun dispose() {
+    inputEditor.dispose()
+    outputEditor.dispose()
+  }
+
+  private enum class ViewMode {
+    INPUT_ONLY,
+    SPLIT,
+  }
+
+  private inner class ShowInputOnlyAction :
+    ToggleAction("Show Input Only", "Show only the input file", AllIcons.General.LayoutEditorOnly) {
+    override fun isSelected(e: AnActionEvent): Boolean = currentViewMode == ViewMode.INPUT_ONLY
+
+    override fun setSelected(e: AnActionEvent, state: Boolean) {
+      if (state) setViewMode(ViewMode.INPUT_ONLY)
+    }
+  }
+
+  private inner class ShowSplitAction :
+    ToggleAction(
+      "Show Split",
+      "Show input and output side by side",
+      AllIcons.General.LayoutEditorPreview,
+    ) {
+    override fun isSelected(e: AnActionEvent): Boolean = currentViewMode == ViewMode.SPLIT
+
+    override fun setSelected(e: AnActionEvent, state: Boolean) {
+      if (state) setViewMode(ViewMode.SPLIT)
+    }
+  }
+}
+
+data class SnippetTestSplitEditorState(
+  val inputState: FileEditorState,
+  val outputState: FileEditorState,
+) : FileEditorState {
+  override fun canBeMergedWith(otherState: FileEditorState, level: FileEditorStateLevel): Boolean {
+    return otherState is SnippetTestSplitEditorState &&
+      inputState.canBeMergedWith(otherState.inputState, level) &&
+      outputState.canBeMergedWith(otherState.outputState, level)
+  }
+}

pkl-internal-intellij-plugin/src/main/resources/META-INF/plugin.xml

@@ -0,0 +1,17 @@
+<idea-plugin>
+  <id>org.pkl.intellij.snippet-test-helper</id>
+  <name>Pkl Snippet Test Helper</name>
+  <vendor>Apple Inc. and the Pkl project authors</vendor>
+
+  <description><![CDATA[
+    Automatically opens snippet test output files when input files are opened.
+
+    This is an internal plugin that is meant for development on the Pkl project itself.
+  ]]></description>
+
+  <depends>com.intellij.modules.platform</depends>
+
+  <extensions defaultExtensionNs="com.intellij">
+    <fileEditorProvider implementation="org.pkl.intellij.SnippetTestEditorProvider"/>
+  </extensions>
+</idea-plugin>