Add configuration option to specify arguments passed to expo start (#991

)

In one of the projects we heard the feedback from, they use `--scheme`
option provided to expo start command. This is necessary for legacy
reasons that they keep using expo this way.

The `--scheme` option makes it so that expo bundler uses the provided
scheme when generating app URLs that we use for launching the app when
expo dev client is detected. We eventually want to avoid relying on
launching dev clients via URL, but the necessary changes only landed in
SDK 52 (expo/expo#33182), so for compatibility
reasons we need to have a way for the schema to be customized on older
versions (and until we add a way to launch dev client with extra
arguments like proposed here expo/expo#33182)

For the time being, the easiest workaround is to extend the launch
configuration and give option to pass additional arguments to expo
start. It doesn't appear like any other args really make sense to be
added, yet giving more genering "args" option seem to require less
explanation.

### How Has This Been Tested: 
1. Launch expo dev client project – make sure nothing breaks
2. Add `--scheme something' as extra args in launch configuration. See
that it wouldn't launch and in debug logs you'll see that the app tries
to launch using `something://` scheme

packages/vscode-extension/package.json

@@ -324,6 +324,10 @@
                 "type": "string",
                 "description": "Location of Metro config relative to the workspace. This is used for using custom configs for e.g. development."
               },
+              "expoStartArgs": {
+                "type": "array",
+                "description": "Extra arguments to pass to Expo start command."
+              },
               "customBuild": {
                 "type": "object",
                 "description": "Configuration for using custom scripts for building and fingerprinting the app.",
@@ -487,6 +491,10 @@
                 "type": "string",
                 "description": "Location of Metro config relative to the workspace. This is used for using custom configs for e.g. development."
               },
+              "expoStartArgs": {
+                "type": "array",
+                "description": "Extra arguments to pass to Expo start command."
+              },
               "ios": {
                 "description": "Provides a way to customize Xcode builds for iOS",
                 "type": "object",

packages/vscode-extension/src/common/LaunchConfig.ts

@@ -9,6 +9,7 @@ export type CustomBuild = {
 export type LaunchConfigurationOptions = {
   appRoot?: string;
   metroConfigPath?: string;
+  expoStartArgs?: string[];
   customBuild?: {
     ios?: CustomBuild;
     android?: CustomBuild;

packages/vscode-extension/src/project/metro.ts

@@ -139,9 +139,18 @@ export class Metro implements Disposable {
     appRootFolder: string,
     libPath: string,
     resetCache: boolean,
+    expoStartExtraArgs: string[] | undefined,
     metroEnv: typeof process.env
   ) {
-    return exec("node", [path.join(libPath, "expo_start.js"), ...(resetCache ? ["--clear"] : [])], {
+    const args = [path.join(libPath, "expo_start.js")];
+    if (resetCache) {
+      args.push("--clear");
+    }
+    if (expoStartExtraArgs) {
+      args.push(...expoStartExtraArgs);
+    }
+
+    return exec("node", args, {
       cwd: appRootFolder,
       env: metroEnv,
       buffer: false,
@@ -207,7 +216,13 @@ export class Metro implements Disposable {
     let bundlerProcess: ChildProcess;
 
     if (shouldUseExpoCLI()) {
-      bundlerProcess = this.launchExpoMetro(appRootFolder, libPath, resetCache, metroEnv);
+      bundlerProcess = this.launchExpoMetro(
+        appRootFolder,
+        libPath,
+        resetCache,
+        launchConfiguration.expoStartArgs,
+        metroEnv
+      );
     } else {
       bundlerProcess = this.launchPackager(appRootFolder, libPath, resetCache, metroEnv);
     }