Use located Flutter instead of PATH flutter for Command.flutter() + s…

…upport FLUTTER_ROOT override

This fixes a TODO where Command.flutter() would always run the version of Flutter from PATH and not the same one we would detect.

This will allow me to fix an issue when using a custom version of DevTools in VS Code (calling "devtools_tool serve") without having to ensure my PATH points at the same version (which it probably doesn't when I'm just opening test apps that use my "normal" checkout of Flutter).

tool/lib/commands/analyze.dart

@@ -20,7 +20,7 @@ class AnalyzeCommand extends Command {
 
   @override
   Future run() async {
-    final sdk = FlutterSdk.getSdk();
+    final sdk = FlutterSdk.current;
     if (sdk == null) {
       print('Unable to locate a Flutter sdk.');
       return 1;

tool/lib/commands/pub_get.dart

@@ -35,7 +35,7 @@ class PubGetCommand extends Command {
 
   @override
   Future run() async {
-    final sdk = FlutterSdk.getSdk();
+    final sdk = FlutterSdk.current;
     if (sdk == null) {
       print('Unable to locate a Flutter sdk.');
       return 1;

tool/lib/commands/update_flutter_sdk.dart

@@ -99,7 +99,7 @@ class UpdateFlutterSdkCommand extends Command {
     );
 
     if (updateLocalFlutter) {
-      final sdk = FlutterSdk.getSdk();
+      final sdk = FlutterSdk.current;
       if (sdk == null) {
         print('Unable to locate a Flutter sdk.');
         return 1;

tool/lib/model.dart

@@ -97,10 +97,15 @@ class DevToolsRepo {
 class FlutterSdk {
   FlutterSdk._(this.sdkPath);
 
+  /// The current located Flutter SDK (or `null` if one could not be found).
+  ///
+  /// Tries to locate from the running Dart VM, FLUTTER_ROOT or searching PATH.
+  static final current = _findSdk();
+
   /// Return the Flutter SDK.
   ///
   /// This can return null if the Flutter SDK can't be found.
-  static FlutterSdk? getSdk() {
+  static FlutterSdk? _findSdk() {
     // TODO(dantup): Everywhere that calls this just prints and exits - should
     //  we just make this throw like DevToolsRepo.getInstance();
     // Look for it relative to the current Dart process.
@@ -127,6 +132,15 @@ class FlutterSdk {
       }
     }
 
+    // Next try FLUTTER_ROOT to allow using a custom flutter (eg. from
+    // `tool/flutter-sdk`) when invoking this without needing to override `PATH`
+    // (it's easier to set override an entire env variable than prepend to one
+    // in some places like the `dart.customDevTools` setting in VS Code).
+    final flutterRootEnv = Platform.environment['FLUTTER_ROOT'];
+    if (flutterRootEnv != null && flutterRootEnv.isNotEmpty) {
+      return FlutterSdk._(flutterRootEnv);
+    }
+
     // Look to see if we can find the 'flutter' command in the PATH.
     // TODO(dantup): This won't work on Windows.
     final result = Process.runSync('which', ['flutter']);

tool/lib/utils.dart

@@ -76,10 +76,13 @@ class CliCommand {
     String args, {
     bool throwOnException = true,
   }) {
+    final sdk = FlutterSdk.current;
+    if (sdk == null) {
+      throw Exception('Unable to locate a Flutter sdk.');
+    }
+
     return CliCommand._(
-      // TODO(dantup): Accept an instance of FlutterSdk instead of relying on
-      //  PATH here?
-      exe: FlutterSdk.flutterExecutableName,
+      exe: sdk.flutterToolPath,
       args: args.split(' '),
       throwOnException: throwOnException,
     );
@@ -224,4 +227,4 @@ extension JoinExtension on List<String> {
   String joinWithNewLine() {
     return '${join('\n')}\n';
   }
-}
+}