Add hot code reload

packages/metals-vscode/package.json

@@ -422,6 +422,14 @@
  }
  },
  "commands": [
+ {
+ "command": "metals.debug.hotCodeReplace",
+ "title": "Hot Code Replace",
+ "icon": {
+ "light": "icons/hot_code_replace.svg",
+ "dark": "icons/hot_code_replace.svg"
+ }
+ },
  {
  "command": "metals.reveal-active-file",
  "category": "Metals",
@@ -695,6 +703,13 @@
  "when": "view == metalsPackages"
  }
  ],
+ "debug/toolBar": [
+ {
+ "command": "metals.debug.hotCodeReplace",
+ "group": "navigation@100",
+ "when": "scalaHotReloadOn"
+ }
+ ],
  "commandPalette": [
  {
  "command": "metals.show-tasty",

packages/metals-vscode/src/debugger/hotCodeReplace.ts

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+// Adapted from https://github.com/microsoft/vscode-java-debug/blob/main/src/hotCodeReplace.ts
+
+import * as vscode from "vscode";
+
+import { DebugSession, commands } from "vscode";
+
+const HCR_ACTIVE = "scalaHotReloadOn";
+
+export function initializeHotCodeReplace() {
+ vscode.debug.onDidStartDebugSession((session) => {
+ if (session?.configuration.noDebug && !vscode.debug.activeDebugSession) {
+ vscode.commands.executeCommand("setContext", HCR_ACTIVE, false);
+ }
+ });
+ vscode.debug.onDidChangeActiveDebugSession((session) => {
+ vscode.commands.executeCommand(
+ "setContext",
+ HCR_ACTIVE,
+ session && !session.configuration.noDebug
+ );
+ });
+}
+
+export async function applyHCR() {
+ const debugSession: DebugSession | undefined =
+ vscode.debug.activeDebugSession;
+ if (!debugSession) {
+ return;
+ }
+
+ if (debugSession.configuration.noDebug) {
+ vscode.window
+ .showWarningMessage(
+ "Failed to apply the changes because hot code replace is not supported by run mode, " +
+ "would you like to restart the program?"
+ )
+ .then((res) => {
+ if (res === "Yes") {
+ vscode.commands.executeCommand("workbench.action.debug.restart");
+ }
+ });
+
+ return;
+ }
+
+ await commands.executeCommand("workbench.action.files.save");
+ const redefineRequest = debugSession.customRequest("redefineClasses");
+ vscode.window.setStatusBarMessage(
+ "$(sync~spin) Applying code changes...",
+ redefineRequest
+ );
+ const response = await redefineRequest;
+
+ if (response?.errorMessage) {
+ vscode.window.showErrorMessage(response.errorMessage);
+ return;
+ }
+
+ if (!response?.changedClasses?.length) {
+ vscode.window.showWarningMessage(
+ "No classes were reloaded, please check the logs"
+ );
+ return;
+ }
+
+ const changed = response.changedClasses.length;
+ vscode.window.setStatusBarMessage(
+ `$(check) ${changed} Class${changed > 1 ? "es" : ""} reloaded`,
+ 5 * 1000
+ );
+}

packages/metals-vscode/src/extension.ts

@@ -105,6 +105,7 @@ import {
  SCALA_LANGID,
 } from "./consts";
 import { ScalaCodeLensesParams } from "./debugger/types";
+import { applyHCR, initializeHotCodeReplace } from "./debugger/hotCodeReplace";
 
 const outputChannel = window.createOutputChannel("Metals");
 const downloadJava = "Download Java";
@@ -1188,6 +1189,10 @@ function launchMetals(
  }
  );
  context.subscriptions.push(decorationsRangesDidChangeDispoasable);
+ registerCommand("metals.debug.hotCodeReplace", () => {
+ applyHCR();
+ });
+ initializeHotCodeReplace();
  },
  (reason) => {
  if (reason instanceof Error) {