Make utf8.encode() have Uint8List return type

Right now `utf8.encode()` has a static return type of `List<int>`
due to extending `Encoding` (which extends `Codec<String, List<int>>`).

We cannot easily change `Encoding` to extend `Codec<String, Uint8List>`
because that would also change `utf8.decode()` to require `Uint8List`
which would be a breaking change.

So instead we override `utf8.encode()` to have more precise return type.

Some parts of our SDK are run using the checked-in SDK, so it cannot
rely on the changed return type yet (until checked-in SDK is rolled).

So we use `const Utf8Encoder().convert()` as a temporary change, as
that already has `Uint8List` return type.

Issue #52801

TEST=ci

CoreLibraryReviewExempt: More precise return type for existing API
Change-Id: I2861d1f0eb3d292d8e3ec8437c0d441a2d2bd193
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/254903
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>

pkg/analysis_server/test/mocks.dart

@@ -68,10 +68,10 @@ class MockProcess implements Process {
   int get pid => _pid;
 
   @override
-  Stream<List<int>> get stderr => Future.value(utf8.encode(_stderr)).asStream();
+  Stream<List<int>> get stderr => Stream<List<int>>.value(utf8.encode(_stderr));
 
   @override
-  Stream<List<int>> get stdout => Future.value(utf8.encode(_stdout)).asStream();
+  Stream<List<int>> get stdout => Stream<List<int>>.value(utf8.encode(_stdout));
 
   @override
   bool kill([ProcessSignal signal = ProcessSignal.sigterm]) {

pkg/analyzer/lib/file_system/memory_file_system.dart

@@ -145,14 +145,14 @@ class MemoryResourceProvider implements ResourceProvider {
     }
 
     _pathToData[path] = _FileData(
-      bytes: utf8.encode(content) as Uint8List,
+      bytes: const Utf8Encoder().convert(content),
       timeStamp: nextStamp++,
     );
     _notifyWatchers(path, ChangeType.MODIFY);
   }
 
   File newFile(String path, String content) {
-    var bytes = utf8.encode(content) as Uint8List;
+    var bytes = const Utf8Encoder().convert(content);
     return newFileWithBytes(path, bytes);
   }
 
@@ -422,7 +422,7 @@ class _MemoryFile extends _MemoryResource implements File {
 
   @override
   void writeAsStringSync(String content) {
-    var bytes = utf8.encode(content) as Uint8List;
+    var bytes = const Utf8Encoder().convert(content);
     writeAsBytesSync(bytes);
   }
 }

pkg/analyzer/lib/file_system/overlay_file_system.dart

@@ -182,7 +182,7 @@ class _OverlayFile extends _OverlayResource implements File {
   Uint8List readAsBytesSync() {
     String? content = provider._getOverlayContent(path);
     if (content != null) {
-      return utf8.encode(content) as Uint8List;
+      return const Utf8Encoder().convert(content);
     }
     return _file.readAsBytesSync();
   }

pkg/analyzer/lib/src/summary2/data_writer.dart

@@ -178,8 +178,7 @@ class BufferedSink {
 
   /// Write the [value] as UTF8 encoded byte array.
   void writeStringUtf8(String value) {
-    var bytes = utf8.encode(value);
-    writeUint8List(bytes as Uint8List);
+    writeUint8List(const Utf8Encoder().convert(value));
   }
 
   void writeStringUtf8Iterable(Iterable<String> items) {

pkg/front_end/lib/src/api_prototype/memory_file_system.dart

@@ -131,10 +131,7 @@ class MemoryFileSystemEntity implements FileSystemEntity {
   /// If no file exists, one is created.  If a file exists already, it is
   /// overwritten.
   void writeAsStringSync(String s) {
-    // Note: the return type of utf8.encode is List<int>, but in practice it
-    // always returns Uint8List.  We rely on that for efficiency, so that we
-    // don't have to make an extra copy.
-    _update(uri, utf8.encode(s) as Uint8List);
+    _update(uri, const Utf8Encoder().convert(s));
   }
 
   void _update(Uri uri, Uint8List data) {

pkg/front_end/test/crashing_test_case_minimizer_impl.dart

@@ -293,7 +293,7 @@ class TestMinimizer {
   Future _tryToMinimizeImpl() async {
     // Set main to be basically empty up front.
     _settings._useInitialFs = true;
-    _fs.data[_mainUri] = utf8.encode("main() {}") as Uint8List;
+    _fs.data[_mainUri] = utf8.encode("main() {}");
     Component initialComponent = await _getInitialComponent();
     print("Compiled initially (without data)");
     // Remove fake cache.
@@ -326,7 +326,7 @@ class TestMinimizer {
           if (_knownByCompiler(uri!)) {
             String parsedString =
                 _getFileAsStringContent(_fs.data[uri]!, _isUriNnbd(uri));
-            _fs.data[uri] = utf8.encode(parsedString) as Uint8List;
+            _fs.data[uri] = utf8.encode(parsedString);
           }
         } catch (e) {
           // crash in scanner/parser --- keep original file. This crash might
@@ -628,8 +628,7 @@ class TestMinimizer {
       for (int i = offsetOfLast; i < withoutInlineableString.length; i++) {
         builder.writeCharCode(withoutInlineableString.codeUnitAt(i));
       }
-      final Uint8List inlinedWithoutChange =
-          utf8.encode(builder.toString()) as Uint8List;
+      final Uint8List inlinedWithoutChange = utf8.encode(builder.toString());
 
       if (!_parsesWithoutError(inlinedWithoutChange, _isUriNnbd(uri))) {
         print("WARNING: Parser error after stuff at ${StackTrace.current}");
@@ -669,8 +668,7 @@ class TestMinimizer {
         for (int i = offsetOfLast; i < withoutInlineableString.length; i++) {
           builder.writeCharCode(withoutInlineableString.codeUnitAt(i));
         }
-        Uint8List inlinedWithChange =
-            utf8.encode(builder.toString()) as Uint8List;
+        Uint8List inlinedWithChange = utf8.encode(builder.toString());
 
         if (!_parsesWithoutError(inlinedWithChange, _isUriNnbd(uri))) {
           print("WARNING: Parser error after stuff at ${StackTrace.current}");
@@ -1015,7 +1013,7 @@ worlds:
 
         bool outlined = false;
         if (textualOutlined != null) {
-          Uint8List candidate = utf8.encode(textualOutlined) as Uint8List;
+          Uint8List candidate = utf8.encode(textualOutlined);
           // Because textual outline doesn't do the right thing for nnbd, only
           // replace if it's syntactically valid.
           if (candidate.length != _fs.data[uri]!.length &&
@@ -1041,8 +1039,7 @@ worlds:
               if (!string.trim().startsWith("//")) stringsLeft.add(string);
             }
 
-            Uint8List candidate =
-                utf8.encode(stringsLeft.join("\n")) as Uint8List;
+            Uint8List candidate = utf8.encode(stringsLeft.join("\n"));
             if (candidate.length != _fs.data[uri]!.length) {
               if (await _shouldQuit()) return;
               _fs.data[uri] = candidate;
@@ -1088,7 +1085,7 @@ worlds:
         }
       }
       string = lines.join("\n");
-      _fs.data[uri] = utf8.encode(string) as Uint8List;
+      _fs.data[uri] = utf8.encode(string);
       if (!await _crashesOnCompile(initialComponent)) {
         // For some reason that didn't work.
         _fs.data[uri] = data;
@@ -1226,7 +1223,7 @@ worlds:
         }
       }
       string = lines.join("\n");
-      Uint8List candidate = utf8.encode(string) as Uint8List;
+      Uint8List candidate = utf8.encode(string);
       if (candidate.length != data.length) {
         _fs.data[uri] = candidate;
         if (!await _crashesOnCompile(initialComponent)) {
@@ -1248,7 +1245,7 @@ worlds:
         while (i < packagesModified.length) {
           var oldEntry = packagesModified.removeAt(i);
           String jsonString = jsonEncoder.convert(jsonModified);
-          candidate = utf8.encode(jsonString) as Uint8List;
+          candidate = utf8.encode(jsonString);
           Uint8List? previous = _fs.data[uri];
           _fs.data[uri] = candidate;
           if (!await _crashesOnCompile(initialComponent)) {
@@ -2071,7 +2068,7 @@ worlds:
       builder.writeCharCode(_dataCacheString!.codeUnitAt(j));
     }
 
-    Uint8List candidate = utf8.encode(builder.toString()) as Uint8List;
+    Uint8List candidate = utf8.encode(builder.toString());
     return candidate;
   }
 }
@@ -2130,7 +2127,7 @@ class _FakeFileSystem extends FileSystem {
       if (tmp[i + 1] == null) {
         data[key] = null;
       } else if (tmp[i + 1] is String) {
-        data[key] = utf8.encode(tmp[i + 1]) as Uint8List;
+        data[key] = utf8.encode(tmp[i + 1]);
       } else {
         data[key] = Uint8List.fromList(new List<int>.from(tmp[i + 1]));
       }

pkg/front_end/test/dartdoc_test_test.dart

@@ -1,5 +1,4 @@
 import 'dart:convert';
-import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/scanner/token.dart';
 import 'package:front_end/src/api_prototype/memory_file_system.dart';
@@ -460,7 +459,7 @@ bool _expectImpl(dynamic actual, dynamic expected, StringBuffer explainer) {
 }
 
 impl.CommentString? extractFirstComment(String test) {
-  Token firstToken = impl.scanRawBytes(utf8.encode(test) as Uint8List);
+  Token firstToken = impl.scanRawBytes(utf8.encode(test));
   Token token = firstToken;
   while (true) {
     CommentToken? comment = token.precedingComments;
@@ -476,6 +475,6 @@ impl.CommentString? extractFirstComment(String test) {
 }
 
 List<impl.Test> extractTests(String test, [Uri? uri]) {
-  return impl.extractTests(utf8.encode(test) as Uint8List,
-      uri ?? new Uri(scheme: "darttest", path: "/foo.dart"));
+  return impl.extractTests(
+      utf8.encode(test), uri ?? new Uri(scheme: "darttest", path: "/foo.dart"));
 }

pkg/front_end/test/fasta/testing/suite.dart

@@ -4,7 +4,7 @@
 
 library fasta.testing.suite;
 
-import 'dart:convert' show jsonDecode, utf8;
+import 'dart:convert' show jsonDecode, utf8, Utf8Encoder;
 import 'dart:io' show Directory, File, Platform;
 import 'dart:typed_data' show Uint8List;
 
@@ -1528,7 +1528,7 @@ class FuzzCompiles
         for (FuzzAstVisitorSorterChunk chunk in fuzzAstVisitorSorter.chunks) {
           sb.writeln(chunk.getSource());
         }
-        Uint8List sortedData = utf8.encode(sb.toString()) as Uint8List;
+        Uint8List sortedData = const Utf8Encoder().convert(sb.toString());
         fs.data[uri] = sortedData;
         incrementalCompiler = new IncrementalCompiler.fromComponent(
             new CompilerContext(compilationSetup.options), platform);
@@ -1644,7 +1644,7 @@ class FuzzCompiles
         print("Skipping $uri -- couldn't find builder for it.");
         continue;
       }
-      Uint8List orgData = fs.data[uri] as Uint8List;
+      Uint8List orgData = fs.data[uri]!;
       FuzzAstVisitorSorter fuzzAstVisitorSorter;
       try {
         fuzzAstVisitorSorter =
@@ -1696,7 +1696,7 @@ class FuzzCompiles
         sb.writeln("import '${uri.pathSegments.last}';");
         sb.writeln(chunk.getSource());
         fs.data[getUriForChunk(currentSubFile)] =
-            utf8.encode(sb.toString()) as Uint8List;
+            const Utf8Encoder().convert(sb.toString());
         print(" => Split into ${getUriForChunk(currentSubFile)}:\n"
             "${sb.toString()}\n-------------\n");
         currentSubFile++;
@@ -1711,7 +1711,7 @@ class FuzzCompiles
       }
       sb.writeln(orgFileOnlyHeaderSb.toString());
       print(" => Main file becomes:\n${sb.toString()}\n-------------\n");
-      fs.data[uri] = utf8.encode(sb.toString()) as Uint8List;
+      fs.data[uri] = const Utf8Encoder().convert(sb.toString());
     }
 
     Result<ComponentResult>? passResult = await performFileInvalidation(

pkg/front_end/tool/dart_doctest_impl.dart

@@ -555,7 +555,7 @@ List<Test> extractTestsFromComment(
 
   Test scanDartDoc(int scanOffset) {
     final Token firstToken =
-        scanRawBytes(utf8.encode(comments.substring(scanOffset)) as Uint8List);
+        scanRawBytes(utf8.encode(comments.substring(scanOffset)));
     final ErrorListener listener = new ErrorListener();
     final Parser parser = new Parser(listener,
         useImplicitCreationExpression: useImplicitCreationExpressionInCfe);

pkg/front_end/tool/perf.dart

@@ -209,7 +209,7 @@ Set<Source> scanReachableFiles(Uri entryUri) {
 /// Loads the file contents of all [files] as bytes.
 Set<Uint8List> loadFileContentsAsBytes(Set<Source> files) {
   return files.map((Source source) {
-    final bytes = utf8.encode(source.contents.data) as Uint8List;
+    final bytes = utf8.encode(source.contents.data);
     // CFE needs files to e 0-terminated.
     return Uint8List(bytes.length + 1)
       ..setRange(0, bytes.length, bytes)

pkg/vm/bin/kernel_service.dart

@@ -701,7 +701,7 @@ String _escapeDependency(Uri uri) {
 }
 
 Uint8List _serializeDependencies(List<Uri> uris) {
-  return utf8.encode(uris.map(_escapeDependency).join(" ")) as Uint8List;
+  return utf8.encode(uris.map(_escapeDependency).join(" "));
 }
 
 Future _processListDependenciesRequest(

sdk/lib/convert/utf.dart

@@ -63,6 +63,11 @@ final class Utf8Codec extends Encoding {
     return decoder.convert(codeUnits);
   }
 
+  /// Encodes the [string] as UTF-8.
+  Uint8List encode(String string) {
+    return const Utf8Encoder().convert(string);
+  }
+
   Utf8Encoder get encoder => const Utf8Encoder();
   Utf8Decoder get decoder {
     // Switch between const objects to avoid allocation.