[dart2wasm] Support --multi-root and --multi-root-scheme flags.

Change-Id: I111748742677073bb3cf4c1655b69cb21d42f546
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274089
Reviewed-by: Joshua Litt <joshualitt@google.com>
Commit-Queue: Jackson Gardner <jacksongardner@google.com>

pkg/dart2wasm/bin/dart2wasm.dart

@@ -50,8 +50,12 @@ final List<Option> options = [
   StringMultiOption(
       "define", (o, values) => o.environment = processEnvironment(values),
       abbr: "D"),
-  StringMultiOption("enable-experiment",
-      (o, values) => o.feExperimentalFlags = processFeExperimentalFlags(values))
+  StringMultiOption(
+      "enable-experiment",
+      (o, values) =>
+          o.feExperimentalFlags = processFeExperimentalFlags(values)),
+  StringOption("multi-root-scheme", (o, value) => o.multiRootScheme = value),
+  UriMultiOption("multi-root", (o, values) => o.multiRoots = values),
 ];
 
 Map<fe.ExperimentalFlag, bool> processFeExperimentalFlags(

pkg/dart2wasm/lib/compile.dart

@@ -4,6 +4,11 @@
 
 import 'dart:typed_data';
 
+import 'package:build_integration/file_system/multi_root.dart'
+    show MultiRootFileSystem;
+
+import 'package:front_end/src/api_prototype/standard_file_system.dart'
+    show StandardFileSystem;
 import 'package:front_end/src/api_unstable/vm.dart'
     show
         CompilerOptions,
@@ -52,6 +57,12 @@ Future<Uint8List?> compileToModule(compiler.CompilerOptions options,
     ..verbose = false
     ..onDiagnostic = diagnosticMessageHandler
     ..nnbdMode = NnbdMode.Strong;
+  if (options.multiRootScheme != null) {
+    compilerOptions.fileSystem = new MultiRootFileSystem(
+        options.multiRootScheme!,
+        options.multiRoots.isEmpty ? [Uri.base] : options.multiRoots,
+        StandardFileSystem.instance);
+  }
 
   if (options.platformPath != null) {
     compilerOptions.sdkSummary = options.platformPath;

pkg/dart2wasm/lib/compiler_options.dart

@@ -18,6 +18,8 @@ class CompilerOptions {
   String outputFile;
   Map<String, String> environment = const {};
   Map<fe.ExperimentalFlag, bool> feExperimentalFlags = const {};
+  String? multiRootScheme;
+  List<Uri> multiRoots = const [];
 
   factory CompilerOptions.defaultOptions() =>
       CompilerOptions(mainUri: Uri(), outputFile: '');

pkg/dart2wasm/lib/option.dart

@@ -51,6 +51,12 @@ class IntOption extends ValueOption<int> {
             defaultsTo: defaultsTo);
 }
 
+class StringOption extends ValueOption<String> {
+  StringOption(String name, void applyToOptions(CompilerOptions o, String v),
+      {String? defaultsTo})
+      : super(name, applyToOptions, (v) => v, defaultsTo: defaultsTo);
+}
+
 class UriOption extends ValueOption<Uri> {
   UriOption(String name, void applyToOptions(CompilerOptions o, Uri v),
       {String? defaultsTo})
@@ -86,3 +92,10 @@ class StringMultiOption extends MultiValueOption<String> {
       : super(name, applyToOptions, (v) => v,
             abbr: abbr, defaultsTo: defaultsTo);
 }
+
+class UriMultiOption extends MultiValueOption<Uri> {
+  UriMultiOption(name, void applyToOptions(CompilerOptions o, List<Uri> v),
+      {Iterable<String>? defaultsTo})
+      : super(name, applyToOptions, (v) => Uri.file(Directory(v).absolute.path),
+            defaultsTo: defaultsTo);
+}

pkg/dart2wasm/pubspec.yaml

@@ -9,6 +9,7 @@ dependencies:
   _fe_analyzer_shared: any
   _js_interop_checks: any
   args: any
+  build_integration: any
   front_end: any
   kernel: any
   vm: any