Reapply "Tweak public APIs and use them in patch_sdk, dart2js, and kernel-service.""

pkg/front_end/lib/src/fasta/parser/native_support.dart

Index: pkg/front_end/lib/src/fasta/parser/native_support.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/native_support.dart b/pkg/front_end/lib/src/fasta/parser/native_support.dart
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+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Implements support for two variants of the native syntax extension.
+///
+///   * The Dart VM variant, where native method bodies have this form:
+///
+///     methodDeclaration() native STRING;
+///
+///   * The Dart2js and DDC variant, where native method bodies have this form:
+///
+///     methodDeclaration() native;
+///
+/// This support is kept separate from parser.dart as this isn't specified in
+/// the Dart Language Specification, also we hope to remove this syntax long
+/// term and replace it with annotations and external declarations.
+library fasta.parser.dart_vm_native;
+
+import '../../scanner/token.dart' show Token;
+
+import '../scanner/token_constants.dart' show STRING_TOKEN;
+
+import '../util/link.dart' show Link;
+
+import 'parser.dart' show optional;
+
+import '../quote.dart' show unescapeString;
+
+/// When parsing a library file, we may encounter a native clause
+/// instead of a function body. This method skips such a clause. The
+/// [expectString] argument is used to choose which variant of the native clause
+/// we expect to parse.
+///
+/// This method is designed to be called when encountering
+/// [ErrorKind.ExpectedBlockToSkip] in [Listener.handleUnrecoverableError].
+Token skipNativeClause(Token token, bool expectString) {
+  if (!optional("native", token)) return null;
+  if (expectString) {
+    token = token.next;
+    if (token.kind != STRING_TOKEN) return null;
+  }
+  if (!optional(";", token.next)) return null;
+  return token;
+}
+
+/// When parsing a library file, we may encounter native getters like
+///
+///     int get length native "List_getLength";
+///
+/// This will result in [identifiers] being
+///
+///     [";", '"List_getLength"', "native", "length", "get"]
+///
+/// Similarly if [expectString] is false, we expect a getter like:
+///
+///     int get length native;
+///
+/// And [identifiers] being
+///
+///     [";", "native", "length", "get"]
+///
+/// This method returns a new list where '"List_getLength"' and "native" are
+/// removed.
+///
+/// This method is designed to be called from [Listener.handleMemberName].
+Link<Token> removeNativeClause(Link<Token> identifiers, bool expectString) {
+  Link<Token> result = identifiers.tail;
+  if (result.isEmpty) return identifiers;
+  if (expectString) {
+    if (result.head.kind != STRING_TOKEN) return identifiers;
+    result = result.tail;
+  }
+  if (result.isEmpty) return identifiers;
+  if (optional('native', result.head)) {
+    return result.tail.prepend(identifiers.head);
+  }
+  return identifiers;
+}
+
+/// When the parser encounters a native clause and expects a string (like in VM
+/// and flutter patch files), this method extracts the native name in that
+/// string.
+String extractNativeMethodName(Token token) {
+  return unescapeString(token.next.lexeme);
+}