Add .mill extension to Scala language support

build.sbt

@@ -55,6 +55,7 @@ lazy val scalaCommunity: sbt.Project =
       scalaImpl % "test->test;compile->compile",
       structureView % "test->test;compile->compile",
       sbtImpl % "test->test;compile->compile",
+      mill % "test->test;compile->compile",
       compilerIntegration % "test->test;compile->compile",
       debugger % "test->test;compile->compile",
       testingSupport % "test->test;compile->compile",
@@ -134,6 +135,11 @@ lazy val sbtApi =
     )
     .withCompilerPluginIn(scalacPatches)
 
+lazy val mill =
+  newProject("mill", file("mill"))
+    .dependsOn(scalaApi, compilerShared, workspaceEntities, scalaImpl % "test->test;compile->compile")
+    .withCompilerPluginIn(scalacPatches)
+
 lazy val codeInsight = newProject(
   "codeInsight",
   file("scala/codeInsight")
@@ -422,7 +428,7 @@ lazy val scalaLanguageUtilsRt: sbt.Project =
 
 lazy val sbtImpl =
   newProject("sbt-impl", file("sbt/sbt-impl"))
-    .dependsOn(sbtApi, scalaImpl % "test->test;compile->compile")
+    .dependsOn(sbtApi, mill, scalaImpl % "test->test;compile->compile")
     .settings(
       intellijPlugins += "org.jetbrains.idea.maven".toPlugin
     )

mill/resources/META-INF/mill.xml

@@ -0,0 +1,10 @@
+<idea-plugin>
+
+    <extensions defaultExtensionNs="com.intellij">
+        <fileType name="mill" language="mill" extensions="mill"
+                  implementationClass="org.jetbrains.mill.language.MillFileType$" fieldName="MODULE$"/>
+        <lang.parserDefinition language="mill" implementationClass="org.jetbrains.mill.language.MillParserDefinition"/>
+<!--        <lang.fileViewProviderFactory language="mill"-->
+<!--                                      implementationClass="org.jetbrains.mill.language.MillFileViewProviderFactory"/>-->
+    </extensions>
+</idea-plugin>

mill/src/org/jetbrains/mill/icons/Icons.java

@@ -0,0 +1,11 @@
+package org.jetbrains.mill.icons;
+
+import javax.swing.*;
+
+import static com.intellij.openapi.util.IconLoader.findIcon;
+    import static com.intellij.openapi.util.IconLoader.getIcon;
+
+public interface Icons {
+    Icon MILL_FILE = getIcon("/org/jetbrains/mill/images/millFile.svg", Icons.class);
+
+}

mill/src/org/jetbrains/mill/language/MillFile.scala

@@ -0,0 +1,6 @@
+package org.jetbrains.mill.language
+
+import com.intellij.psi.impl.source.PsiFileWithStubSupport
+
+trait MillFile extends PsiFileWithStubSupport {
+}

mill/src/org/jetbrains/mill/language/MillFileImpl.scala

@@ -0,0 +1,28 @@
+package org.jetbrains.mill
+package language
+
+
+import com.intellij.openapi.application.ApplicationManager
+import com.intellij.openapi.module.{Module, ModuleManager, ModuleUtilCore}
+import com.intellij.openapi.roots.ProjectRootManager
+import com.intellij.psi._
+import com.intellij.psi.search.{GlobalSearchScope, searches}
+import org.jetbrains.annotations.NonNls
+import org.jetbrains.plugins.scala.caches.{ModTracker, cached, cachedInUserData}
+import org.jetbrains.plugins.scala.extensions.PsiClassExt
+import org.jetbrains.plugins.scala.lang.psi.ScDeclarationSequenceHolder
+import org.jetbrains.plugins.scala.lang.psi.api.toplevel.typedef.ScTypeDefinition
+import org.jetbrains.plugins.scala.lang.psi.impl._
+import org.jetbrains.plugins.scala.project.{ModuleExt, ScalaFeatures}
+import org.jetbrains.sbt.project.SbtBuildModuleUriProvider
+import org.jetbrains.sbt.project.module.SbtModule.{Build, Imports}
+
+import scala.jdk.CollectionConverters._
+
+final class MillFileImpl private[language](provider: FileViewProvider)
+  extends ScalaFileImpl(provider, MillFileType)
+    with MillFile {
+
+
+
+}

mill/src/org/jetbrains/mill/language/MillFileType.scala

@@ -0,0 +1,10 @@
+package org.jetbrains.mill.language
+
+import org.jetbrains.plugins.scala.{LanguageFileTypeBase, ScalaLanguage}
+import org.jetbrains.mill.icons.Icons
+
+import javax.swing.Icon
+
+object MillFileType extends LanguageFileTypeBase(MillLanguage.INSTANCE) {
+  override def getIcon: Icon = Icons.MILL_FILE
+}

mill/src/org/jetbrains/mill/language/MillFileViewProviderFactory.scala

@@ -0,0 +1,15 @@
+package org.jetbrains.mill
+package language
+
+import com.intellij.lang.Language
+import com.intellij.openapi.vfs.VirtualFile
+import com.intellij.psi.{FileViewProviderFactory, PsiManager, SingleRootFileViewProvider}
+
+final class MillFileViewProviderFactory extends FileViewProviderFactory {
+
+  override def createFileViewProvider(file: VirtualFile,
+                                      language: Language,
+                                      manager: PsiManager,
+                                      eventSystemEnabled: Boolean): SingleRootFileViewProvider =
+    new SingleRootFileViewProvider(manager, file, eventSystemEnabled, language) {}
+}

mill/src/org/jetbrains/mill/language/MillLanguage.java

@@ -0,0 +1,13 @@
+package org.jetbrains.mill.language;
+
+import com.intellij.lang.Language;
+import org.jetbrains.plugins.scala.ScalaLanguage;
+
+public final class MillLanguage extends Language {
+
+    public static final MillLanguage INSTANCE = new MillLanguage();
+
+    private MillLanguage() {
+        super(ScalaLanguage.INSTANCE, "mill");
+    }
+}

mill/src/org/jetbrains/mill/language/MillParserDefinition.scala

@@ -0,0 +1,19 @@
+package org.jetbrains.mill
+package language
+
+import com.intellij.openapi.project.Project
+import com.intellij.psi.FileViewProvider
+import com.intellij.psi.tree.IFileElementType
+import org.jetbrains.plugins.scala.lang.lexer.ScalaLexer
+import org.jetbrains.plugins.scala.lang.parser.{ScalaParser, ScalaParserDefinitionBase}
+
+final class MillParserDefinition extends ScalaParserDefinitionBase {
+
+  override def createLexer(project: Project) = new ScalaLexer(false, project)
+
+  override def createParser(project: Project) = new ScalaParser(isScala3 = false)
+
+  override val getFileNodeType = new IFileElementType("mill.FILE", MillLanguage.INSTANCE)
+
+  override def createFile(viewProvider: FileViewProvider) = new MillFileImpl(viewProvider)
+}

pluginXml/resources/META-INF/plugin.xml

@@ -56,6 +56,7 @@
     <xi:include href="/META-INF/sbt-api.xml" xpointer="xpointer(/idea-plugin/*)"/>
     <xi:include href="/META-INF/scala-plugin-common.xml" xpointer="xpointer(/idea-plugin/*)"/>
     <xi:include href="/META-INF/sbt.xml" xpointer="xpointer(/idea-plugin/*)"/>
+    <xi:include href="/META-INF/mill.xml" xpointer="xpointer(/idea-plugin/*)"/>
     <xi:include href="/META-INF/BSP.xml" xpointer="xpointer(/idea-plugin/*)"/>
     <xi:include href="/META-INF/codeInsight.xml" xpointer="xpointer(/idea-plugin/*)"/>
     <xi:include href="/META-INF/conversion.xml" xpointer="xpointer(/idea-plugin/*)"/>