Move parser helper classes to own files and clean them up.

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

+// 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.
+
+library fasta.parser.type_continuation;
+
+import '../problems.dart' show unhandled;

[ahe, 2017/07/18 10:13:38]

This import causes the parser to depend on CompilerContext which we don't want
as dart2js relies directly on the parser (without setting up a compiler
context).

+
+import 'formal_parameter_kind.dart' show FormalParameterKind;
+
+/// Indication of how the parser should continue after (attempting) to parse a
+/// type.
+///
+/// Depending on the continuation, the parser may not parse a type at all.
+enum TypeContinuation {
+  /// Indicates that a type is unconditionally expected.
+  Required,
+
+  /// Indicates that a type may follow. If the following matches one of these
+  /// productions, it is parsed as a type:
+  ///
+  ///  - `'void'`
+  ///  - `'Function' ( '(' | '<' )`
+  ///  - `identifier ('.' identifier)? ('<' ... '>')? identifer`
+  ///
+  /// Otherwise, do nothing.
+  Optional,
+
+  /// Same as [Optional], but we have seen `var`.
+  OptionalAfterVar,
+
+  /// Indicates that the keyword `typedef` has just been seen, and the parser
+  /// should parse the following as a type unless it is followed by `=`.
+  Typedef,
+
+  /// Indicates that what follows is either a local declaration or an
+  /// expression.
+  ExpressionStatementOrDeclaration,
+
+  /// Indicates that the keyword `const` has just been seen, and what follows
+  /// may be a local variable declaration or an expression.
+  ExpressionStatementOrConstDeclaration,
+
+  /// Indicates that the parser is parsing an expression and has just seen an
+  /// identifier.
+  SendOrFunctionLiteral,
+
+  /// Indicates that the parser has just parsed `for '('` and is looking to
+  /// parse a variable declaration or expression.
+  VariablesDeclarationOrExpression,
+
+  /// Indicates that an optional type followed by a normal formal parameter is
+  /// expected.
+  NormalFormalParameter,
+
+  /// Indicates that an optional type followed by an optional positional formal
+  /// parameter is expected.
+  OptionalPositionalFormalParameter,
+
+  /// Indicates that an optional type followed by a named formal parameter is
+  /// expected.
+  NamedFormalParameter,
+
+  /// Same as [NormalFormalParameter], but we have seen `var`.
+  NormalFormalParameterAfterVar,
+
+  /// Same as [OptionalPositionalFormalParameter], but we have seen `var`.
+  OptionalPositionalFormalParameterAfterVar,
+
+  /// Same as [NamedFormalParameter], but we have seen `var`.
+  NamedFormalParameterAfterVar,
+}
+
+TypeContinuation typeContiunationFromFormalParameterKind(
+    FormalParameterKind type) {
+  if (type == null) return null;
+  switch (type) {
+    case FormalParameterKind.mandatory:
+      return TypeContinuation.NormalFormalParameter;
+
+    case FormalParameterKind.optionalNamed:
+      return TypeContinuation.NamedFormalParameter;
+
+    case FormalParameterKind.optionalPositional:
+      return TypeContinuation.OptionalPositionalFormalParameter;
+  }
+  return unhandled(
+      "$type", "typeContiunationFromFormalParameterKind", -1, null);
+}