Let VSCode start the language server

We used to start the language server with `launchIDE`. However, this
means that the language server is dependent of sbt being running and
configured, which is not a good user experience for newcomers.

For newcomers, we want the language server to start when they create a
new Scala file in an empty directory, for instance, which means that no
build is already configured.

This commits takes us closer to this experience by using `load-plugin`
to inject the Dotty plugin. This means that the Dotty plugin can now be
loaded even if there's no build configured, which happens if the user
opens VSCode in an empty directory, for instance.

Author: Duhemm

vscode-dotty/package.json

@@ -24,6 +24,7 @@
   ],
   "main": "./out/src/extension",
   "activationEvents": [
+    "onLanguage:scala",
     "workspaceContains:.dotty-ide.json"
   ],
   "languages": [
@@ -50,7 +51,7 @@
     "vscode:prepublish": "npm install && ./node_modules/.bin/tsc -p ./",
     "compile": "./node_modules/.bin/tsc -p ./",
     "test": "node ./node_modules/vscode/bin/test",
-    "postinstall": "node ./node_modules/vscode/bin/install && curl -L -o out/coursier https://github.com/coursier/coursier/raw/v1.0.0/coursier"
+    "postinstall": "node ./node_modules/vscode/bin/install && curl -L -o out/coursier https://github.com/coursier/coursier/raw/v1.0.0/coursier && curl -L -o out/load-plugin.jar https://github.com/scalacenter/load-plugin/releases/download/v0.1.0/load-plugin_2.12-0.1.0.jar"
   },
   "extensionDependencies": [
     "daltonjorge.scala"

vscode-dotty/src/extension.ts

@@ -17,12 +17,9 @@ export function activate(context: ExtensionContext) {
   outputChannel = vscode.window.createOutputChannel('Dotty Language Client');
 
   const artifactFile = `${vscode.workspace.rootPath}/.dotty-ide-artifact`
+  const defaultArtifact = "ch.epfl.lamp:dotty-language-server_0.8:0.8.0-bin-SNAPSHOT"
   fs.readFile(artifactFile, (err, data) => {
-    if (err) {
-      outputChannel.append(`Unable to parse ${artifactFile}`)
-      throw err
-    }
-    const artifact = data.toString().trim()
+    const artifact = err ? defaultArtifact : data.toString().trim()
 
     if (process.env['DLS_DEV_MODE']) {
       const portFile = `${vscode.workspace.rootPath}/.dotty-ide-dev-port`
@@ -77,15 +74,51 @@ function fetchAndRun(artifact: string) {
         throw new Error(msg)
       }
 
-      run({
-        command: "java",
-        args: ["-classpath", classPath, "dotty.tools.languageserver.Main", "-stdio"]
+      configureIDE().then((res) => {
+        run({
+          command: "java",
+          args: ["-classpath", classPath, "dotty.tools.languageserver.Main", "-stdio"]
+        })
       })
     })
     return coursierPromise
   })
 }
 
+function configureIDE() {
+  const coursierPath = path.join(extensionContext.extensionPath, './out/coursier');
+  const loadPluginPath = path.join(extensionContext.extensionPath, './out/load-plugin.jar');
+
+  return vscode.window.withProgress({
+    location: vscode.ProgressLocation.Window,
+    title: 'Configuring IDE...'
+  }, (progress) => {
+
+    const sbtPromise =
+      cpp.spawn("java", [
+          "-jar", coursierPath,
+          "launch",
+          "org.scala-sbt:sbt-launch:1.1.2", "--",
+          "apply -cp " + loadPluginPath + " ch.epfl.scala.loadplugin.LoadPlugin",
+          "set every scalaVersion := \"0.8.0-bin-SNAPSHOT\"",
+          "load-plugin ch.epfl.lamp:sbt-dotty:0.2.0-SNAPSHOT dotty.tools.sbtplugin.DottyPlugin",
+          "load-plugin ch.epfl.lamp:sbt-dotty:0.2.0-SNAPSHOT dotty.tools.sbtplugin.DottyIDEPlugin",
+          "configureIDE"
+      ])
+    const sbtProc = sbtPromise.childProcess
+
+    sbtProc.on('close', (code: number) => {
+      if (code != 0) {
+        let msg = "Configuring the IDE failed."
+        outputChannel.append(msg)
+        throw new Error(msg)
+      }
+    })
+
+    return sbtPromise;
+  })
+}
+
 function run(serverOptions: ServerOptions) {
   const clientOptions: LanguageClientOptions = {
     documentSelector: ['scala'],