Merge pull request #1419 from iusildra/add-hot-code-reload

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) {