Restructure parser error handling and recovery.

pkg/dart_parser/lib/src/listener.dart

Index: pkg/dart_parser/lib/src/listener.dart
diff --git a/pkg/dart_parser/lib/src/listener.dart b/pkg/dart_parser/lib/src/listener.dart
index 9d656bbcf94dd29adb6d08d793bf9ed2e8dfaf18..63d0188d6f021a7f083afb978300b04a372429f8 100644
--- a/pkg/dart_parser/lib/src/listener.dart
+++ b/pkg/dart_parser/lib/src/listener.dart
@@ -4,18 +4,9 @@
 
 library dart_parser.listener;
 
-import 'package:dart_scanner/src/precedence.dart' show
-    EOF_INFO,
-    IDENTIFIER_INFO;
-
 import 'package:dart_scanner/src/token.dart' show
-    BadInputToken,
     BeginGroupToken,
-    ErrorToken,
-    StringToken,
-    Token,
-    UnmatchedToken,
-    UnterminatedToken;
+    Token;
 
 import 'error_kind.dart' show
     ErrorKind;
@@ -760,216 +751,28 @@ class Listener {
     logEvent("YieldStatement");
   }
 
-  // TODO(ahe): Rename to `handleUnexpected`.
-  Token expected(String string, Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected '$string', but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Move away from this class.
-  Token synthesizeIdentifier(Token token) {
-    Token synthesizedToken = new StringToken.fromString(
-        IDENTIFIER_INFO, '?', token.charOffset);
-    synthesizedToken.next = token.next;
-    return synthesizedToken;
-  }
-
-  // TODO(ahe): Rename to `handleIdentifierExpected`.
-  Token expectedIdentifier(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected identifier, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleTypeExpected`.
-  Token expectedType(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a type, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleExpressionExpected`.
-  Token expectedExpression(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected an expression, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Merge with `handleUnexpected` (nee `expected`).
-  Token unexpected(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("unexpected token '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleBlockToSkipExpected`.
-  Token expectedBlockToSkip(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a block, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleFunctionBodyExpected`.
-  Token expectedFunctionBody(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a function body, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleClassBodyExpected`.
-  Token expectedClassBody(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a class body, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleClassBodyToSkipExpected`.
-  Token expectedClassBodyToSkip(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a class body, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleDeclarationExpected`.
-  Token expectedDeclaration(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("expected a declaration, but got '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Rename to `handleUnmatched`.
-  Token unmatched(Token token) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      error("unmatched '${token.value}'", token);
-    }
-    return skipToEof(token);
-  }
-
-  // TODO(ahe): Move away from this class.
-  Token skipToEof(Token token) {
-    while (!identical(token.info, EOF_INFO)) {
-      token = token.next;
-    }
-    return token;
-  }
-
-  // TODO(ahe): Merge with `handleError` (nee `reportError`).
-  void error(String message, Token token) {
-    throw new ParserError.fromTokens(
-        token, token, ErrorKind.Unspecified, {'text': message});
-  }
-
-  // TODO(ahe): Rename to `handleError`.
-  void reportError(Token token, ErrorKind kind, [Map arguments = const {}]) {
-    if (token is ErrorToken) {
-      reportErrorToken(token);
-    } else {
-      reportErrorHelper(token, kind, arguments);
-    }
-  }
-
-  // TODO(ahe): Move away from this class.
-  void reportErrorHelper(Token token, ErrorKind kind, Map arguments) {
-    recoverableErrors.add(
-        new ParserError.fromTokens(token, token, kind, arguments));
+  /// An unrecoverable error is an error that the parser can't recover from
+  /// itself, and recovery is left to the listener. If the listener can
+  /// recover, it should return a non-null continuation token. Error recovery
+  /// is tightly coupled to the parser implementation, so to recover from an
+  /// error, one must carefully examine the code in the parser that generates
+  /// the error.
+  ///
+  /// If the listener can't recover, it can throw an exception or return
+  /// `null`. In the latter case, the parser simply skips to EOF which will
+  /// often result in additional parser errors as the parser returns from its
+  /// recursive state.
+  Token handleUnrecoverableError(Token token, ErrorKind kind, Map arguments) {
+    throw new ParserError.fromTokens(token, token, kind, arguments);
   }
 
-  // TODO(ahe): Move away from this class.
-  void reportErrorToken(ErrorToken token) {
-    if (token is BadInputToken) {
-      String hex = token.character.toRadixString(16);
-      if (hex.length < 4) {
-        String padding = "0000".substring(hex.length);
-        hex = "$padding$hex";
-      }
-      reportErrorHelper(
-          token, ErrorKind.InvalidInputCharacter, {'characterHex': hex});
-    } else if (token is UnterminatedToken) {
-      ErrorKind kind;
-      var arguments = const {};
-      switch (token.start) {
-        case '1e':
-          kind = ErrorKind.MissingExponent;
-          break;
-        case '"':
-        case "'":
-        case '"""':
-        case "'''":
-        case 'r"':
-        case "r'":
-        case 'r"""':
-        case "r'''":
-          kind = ErrorKind.UnterminatedString;
-          arguments = {'quote': token.start};
-          break;
-        case '0x':
-          kind = ErrorKind.ExpectedHexDigit;
-          break;
-        case r'$':
-          kind = ErrorKind.MalformedStringLiteral;
-          break;
-        case '/*':
-          kind = ErrorKind.UnterminatedComment;
-          break;
-        default:
-          kind = ErrorKind.UnterminatedToken;
-          break;
-      }
-      reportErrorHelper(token, kind, arguments);
-    } else if (token is UnmatchedToken) {
-      String begin = token.begin.value;
-      String end = closeBraceFor(begin);
-      reportErrorHelper(
-          token, ErrorKind.UnmatchedToken, {'begin': begin, 'end': end});
-    } else {
-      error(token.assertionMessage, token);
-    }
+  /// The parser noticed a syntax error, but was able to recover from it.
+  void handleRecoverableError(Token token, ErrorKind kind, Map arguments) {
+    recoverableErrors.add(
+        new ParserError.fromTokens(token, token, kind, arguments));
   }
 }
 
-String closeBraceFor(String openBrace) {
-  return const {
-    '(': ')',
-    '[': ']',
-    '{': '}',
-    '<': '>',
-    r'${': '}',
-  }[openBrace];
-}
-
 class ParserError {
   /// Character offset from the beginning of file where this error starts.
   final int beginOffset;