improvement: Use jar based coursier if unable to download native image

packages/metals-languageclient/src/__tests__/setupCoursier.test.ts

@@ -49,6 +49,7 @@ describe("setupCoursier", () => {
     const { coursier, javaHome } = await setupCoursier(
       "17",
       tmpDir,
+      process.cwd(),
       new LogOutputChannel()
     );
     expect(fs.existsSync(coursier)).toBeTruthy;

packages/metals-languageclient/src/fetchMetals.ts

@@ -21,7 +21,7 @@ interface PackedChildPromise {
 export async function fetchMetals({
   serverVersion,
   serverProperties,
-  javaConfig: { javaOptions, coursier, extraEnv },
+  javaConfig: { javaOptions, coursier, extraEnv, javaPath },
   outputChannel,
 }: FetchMetalsOptions): Promise<PackedChildPromise> {
   const serverDependency = calcServerDependency(serverVersion);
@@ -35,11 +35,7 @@ export async function fetchMetals({
     );
   }
 
-  // Convert Java properties to the "-J" argument form used by Coursier
-  const javaArgs = javaOptions.concat(fetchProperties).map((p) => `-J${p}`);
-
   const coursierArgs = [
-    ...javaArgs,
     "fetch",
     "-p",
     "--ttl",
@@ -64,9 +60,22 @@ export async function fetchMetals({
     },
   };
 
-  return {
-    promise: spawn(coursier, coursierArgs, environment),
-  };
+  if (coursier.endsWith(".jar")) {
+    const jarArgs = [
+      ...javaOptions,
+      ...fetchProperties,
+      "-Dfile.encoding=UTF-8",
+      "-jar",
+      coursier,
+    ].concat(coursierArgs);
+    return { promise: spawn(javaPath, jarArgs, environment) };
+  } else {
+    // Convert Java properties to the "-J" argument form used by Coursier
+    const javaArgs = javaOptions.concat(fetchProperties).map((p) => `-J${p}`);
+    return {
+      promise: spawn(coursier, javaArgs.concat(coursierArgs), environment),
+    };
+  }
 }
 
 export function calcServerDependency(serverVersion: string): string {

packages/metals-languageclient/src/setupCoursier.ts

@@ -18,6 +18,7 @@ const coursierCommit = "11b428f35ca84a598ca30cce1c35ae4f375e5ee3";
 export async function setupCoursier(
   javaVersion: JavaVersion,
   coursierFetchPath: string,
+  extensionPath: string,
   output: OutputChannel
 ): Promise<{ coursier: string; javaHome: string }> {
   const handleOutput = (out: Buffer) => {
@@ -40,11 +41,14 @@ export async function setupCoursier(
 
     return fetchCoursier(coursierFetchPath, handleOutput)
       .then(() => defaultCoursier)
-      .catch((err) => {
+      .catch((_) => {
         output.appendLine(
           "Failed to fetch coursier. You may want to try installing coursier manually and adding it to PATH."
         );
-        throw err;
+        output.appendLine(
+          "Will try to use jar based coursier if Java is available on the machine."
+        );
+        return undefined;
       });
   };
 
@@ -67,12 +71,12 @@ export async function setupCoursier(
     return ((await getJavaPath).stdout as string).trim();
   };
 
-  const coursier = await resolveCoursier();
+  var coursier = await resolveCoursier();
   output.appendLine(`Using coursier located at ${coursier}`);
 
   var javaHome = await getJavaHome(javaVersion, output);
 
-  if (!javaHome) {
+  if (!javaHome && coursier) {
     output.appendLine(
       `No installed java with version ${javaVersion} found. Will fetch one using coursier.`
     );
@@ -81,7 +85,18 @@ export async function setupCoursier(
 
   output.appendLine(`Using Java Home: ${javaHome}`);
 
-  return { coursier, javaHome };
+  /* If we couldn't download coursier, but we have Java
+   * we can still fall back to jar based launcher.
+   */
+  if (!coursier && javaHome) {
+    coursier = path.join(extensionPath, "./coursier-fallback.jar");
+  }
+
+  if (javaHome && coursier) return { coursier, javaHome };
+  else
+    throw Error(
+      "Cannot resolve Java home or coursier, please provide at least JAVA_HOME."
+    );
 }
 
 export async function validateCoursier(

packages/metals-vscode/src/extension.ts

@@ -142,6 +142,7 @@ export async function activate(context: ExtensionContext): Promise<void> {
         await fetchAndLaunchMetals(context, serverVersion, javaVersion);
       } catch (err) {
         outputChannel.appendLine(`${err}`);
+        window.showErrorMessage(`${err}`);
       }
     }
   );
@@ -217,6 +218,7 @@ async function fetchAndLaunchMetals(
   const { coursier, javaHome } = await metalsLanguageClient.setupCoursier(
     javaVersion,
     metalsDirPath,
+    context.extensionPath,
     outputChannel
   );