Expect 'extends' in type parameters declaration and recover, issue 341

compiler/java/com/google/dart/compiler/parser/DartParser.java

Index: compiler/java/com/google/dart/compiler/parser/DartParser.java
diff --git a/compiler/java/com/google/dart/compiler/parser/DartParser.java b/compiler/java/com/google/dart/compiler/parser/DartParser.java
index e6a5ad2572395649e938d7d11ce675f1b2724a20..5ed8bcc6ad19b246737c2142d83042a18d3c82f7 100644
--- a/compiler/java/com/google/dart/compiler/parser/DartParser.java
+++ b/compiler/java/com/google/dart/compiler/parser/DartParser.java
@@ -249,21 +249,34 @@ public class DartParser extends CompletionHooksParserBase {
     parseDirectives(unit);
 
     while (!EOS()) {
-      DartNode node = null;
-      beginTopLevelElement();
-      isParsingInterface = false;
-      if (optionalPseudoKeyword(CLASS_KEYWORD)) {
-        node = done(parseClass());
-      } else if (optionalPseudoKeyword(INTERFACE_KEYWORD)) {
-        isParsingInterface = true;
-        node = done(parseClass());
-      } else if (optionalPseudoKeyword(TYPEDEF_KEYWORD)) {
-        node = done(parseFunctionTypeAlias());
-      } else {
-        node = done(parseFieldOrMethod(false));
-      }
-      if (node != null) {
-        unit.addTopLevelNode(node);
+      try {
+        DartNode node = null;
+        beginTopLevelElement();
+        isParsingInterface = false;
+        if (optionalPseudoKeyword(CLASS_KEYWORD)) {
+          node = done(parseClass());
+        } else if (optionalPseudoKeyword(INTERFACE_KEYWORD)) {
+          isParsingInterface = true;
+          node = done(parseClass());
+        } else if (optionalPseudoKeyword(TYPEDEF_KEYWORD)) {
+          node = done(parseFunctionTypeAlias());
+        } else {
+          node = done(parseFieldOrMethod(false));
+        }
+        if (node != null) {
+          unit.addTopLevelNode(node);
+        }
+      } catch (ParserException e) {
+        Location beginLocation = ctx.getTokenLocation();
+        // Find known top level element to restart parsing.
+        while (peek(0) != Token.EOS && !peekTopLevelKeyword(0)) {
+          next();
+        }
+        // Report skipped source.
+        Location endLocation = ctx.getTokenLocation();
+        reportError(new DartCompilationError(ctx.getSource(),
+            new Location(beginLocation.getBegin(), endLocation.getEnd()),
+            ParserErrorCode.SKIPPED_SOURCE));
       }
     }
     expect(Token.EOS);
@@ -271,6 +284,16 @@ public class DartParser extends CompletionHooksParserBase {
   }
 
   /**
+   * @return <code>true</code> if token at given position is keyword which can be used only on top
+   *         level.
+   */
+  private boolean peekTopLevelKeyword(int n) {
+    return peekPseudoKeyword(n, CLASS_KEYWORD)
+        || peekPseudoKeyword(n, INTERFACE_KEYWORD)
+        || peekPseudoKeyword(n, TYPEDEF_KEYWORD);
+  }
+
+  /**
    * A version of the parser which only parses the directives of a library.
    *
    * TODO(jbrosenberg): consider parsing the whole file here, in order to avoid
@@ -435,18 +458,55 @@ public class DartParser extends CompletionHooksParserBase {
     List<DartTypeParameter> types = new ArrayList<DartTypeParameter>();
     expect(Token.LT);
     do {
-      beginTypeParameter();
-      DartIdentifier name = parseIdentifier();
-      DartTypeNode bound = null;
-      if (optionalPseudoKeyword(EXTENDS_KEYWORD)) {
-        bound = parseTypeAnnotation();
-      }
-      types.add(done(new DartTypeParameter(name, bound)));
+      DartTypeParameter typeParameter = parseTypeParameter();
+      types.add(typeParameter);
     } while (optional(Token.COMMA));
     expect(Token.GT);
     return types;
   }
 
+  // XXX

[zundel, 2011/11/18 18:04:33]

spurious comment

+  /**
+   * Parses single {@link DartTypeParameter} for {@link #parseTypeParameters()}.
+   */
+  private DartTypeParameter parseTypeParameter() {
+    beginTypeParameter();
+    DartIdentifier name = parseIdentifier();
+    // Try to parse bound.
+    DartTypeNode bound = null;
+    if (peek(0) != Token.EOS && peek(0) != Token.COMMA && peek(0) != Token.GT) {
+      if (optionalPseudoKeyword(EXTENDS_KEYWORD)) {
+        // OK, this is EXTENDS_KEYWORD, parse type.
+        bound = parseTypeAnnotation();
+      } else if (peekTopLevelKeyword(0)) {
+        // class Foo<T{cursor}   class Bar {}
+        // User is typing type parameters now, next is top level element.
+        // Stop parsing of current top level element and restart from the next one.
+        throw new ParserException();
+      } else if (peek(0) == Token.IDENTIFIER && (peek(1) == Token.COMMA || peek(1) == Token.GT)) {
+        // <X exte{cursor}>
+        // User tries to type "extends", but it is not finished yet.
+        // Report problem and try to continue.
+        reportErrorWithoutAdvancing(ParserErrorCode.EXPECTED_EXTENDS);

[zundel, 2011/11/18 18:04:33]

Using reportErrorWithoutAdvancing() and then calling next()  seems a slight bit
more awkward than;

next();
reportError(ErrorCode)

which I think does the same thing.

+        next();
+      } else if (peek(0) == Token.IDENTIFIER && peek(1) == Token.IDENTIFIER && (peek(2) == Token.COMMA || peek(2) == Token.GT)) {
+        // <X somethingLikeExtends Type>
+        // User mistyped word "extends" or it is not finished yet.
+        // Report problem and try to continue.
+        reportErrorWithoutAdvancing(ParserErrorCode.EXPECTED_EXTENDS);
+        next();
+        bound = parseTypeAnnotation();
+      } else {
+        // Something else, restart parsing from next top level element.
+        reportErrorWithoutAdvancing(ParserErrorCode.EXPECTED_EXTENDS);
+        next();
+        throw new ParserException();
+      }
+    }
+    // Ready to create DartTypeParameter.
+    return done(new DartTypeParameter(name, bound));
+  }
+
   private List<DartTypeParameter> parseTypeParametersOpt() {
     return (peek(0) == Token.LT)
         ? parseTypeParameters()