/** <summary>Attempt to recover from a single missing or extra token.</summary> * * EXTRA TOKEN * * LA(1) is not what we are looking for. If LA(2) has the right token, * however, then assume LA(1) is some extra spurious token. Delete it * and LA(2) as if we were doing a normal match(), which advances the * input. * * MISSING TOKEN * * If current token is consistent with what could come after * ttype then it is ok to "insert" the missing token, else throw * exception For example, Input "i=(3;" is clearly missing the * ')'. When the parser returns from the nested call to expr, it * will have call chain: * * stat -> expr -> atom * * and it will be trying to match the ')' at this point in the * derivation: * * => ID '=' '(' INT ')' ('+' atom)* ';' * ^ * match() will see that ';' doesn't match ')' and report a * mismatched token error. To recover, it sees that LA(1)==';' * is in the set of tokens that can follow the ')' token * reference in rule atom. It can assume that you forgot the ')'. */ protected virtual object RecoverFromMismatchedToken(IIntStream input, int ttype, BitSet follow) { RecognitionException e = null; // if next token is what we are looking for then "delete" this token if (MismatchIsUnwantedToken(input, ttype)) { e = new UnwantedTokenException(ttype, input, TokenNames); /* * System.err.println("recoverFromMismatchedToken deleting "+ * ((TokenStream)input).LT(1)+ * " since "+((TokenStream)input).LT(2)+" is what we want"); */ BeginResync(); input.Consume(); // simply delete extra token EndResync(); ReportError(e); // report after consuming so AW sees the token in the exception // we want to return the token we're actually matching object matchedSymbol = GetCurrentInputSymbol(input); input.Consume(); // move past ttype token as if all were ok return(matchedSymbol); } // can't recover with single token deletion, try insertion if (MismatchIsMissingToken(input, follow)) { object inserted = GetMissingSymbol(input, e, ttype, follow); e = new MissingTokenException(ttype, input, inserted); ReportError(e); // report after inserting so AW sees the token in the exception return(inserted); } // even that didn't work; must throw the exception e = new MismatchedTokenException(ttype, input, TokenNames); throw e; }
/** <summary>What error message should be generated for the various exception types?</summary> * * <remarks> * Not very object-oriented code, but I like having all error message * generation within one method rather than spread among all of the * exception classes. This also makes it much easier for the exception * handling because the exception classes do not have to have pointers back * to this object to access utility routines and so on. Also, changing * the message for an exception type would be difficult because you * would have to subclassing exception, but then somehow get ANTLR * to make those kinds of exception objects instead of the default. * This looks weird, but trust me--it makes the most sense in terms * of flexibility. * * For grammar debugging, you will want to override this to add * more information such as the stack frame with * getRuleInvocationStack(e, this.getClass().getName()) and, * for no viable alts, the decision description and state etc... * * Override this to change the message generated for one or more * exception types. * </remarks> */ public virtual string GetErrorMessage(RecognitionException e, string[] tokenNames) { string msg = e.Message; if (e is UnwantedTokenException) { UnwantedTokenException ute = (UnwantedTokenException)e; string tokenName = "<unknown>"; if (ute.Expecting == TokenTypes.EndOfFile) { tokenName = "EndOfFile"; } else { tokenName = tokenNames[ute.Expecting]; } msg = "extraneous input " + GetTokenErrorDisplay(ute.UnexpectedToken) + " expecting " + tokenName; } else if (e is MissingTokenException) { MissingTokenException mte = (MissingTokenException)e; string tokenName = "<unknown>"; if (mte.Expecting == TokenTypes.EndOfFile) { tokenName = "EndOfFile"; } else { tokenName = tokenNames[mte.Expecting]; } msg = "missing " + tokenName + " at " + GetTokenErrorDisplay(e.Token); } else if (e is MismatchedTokenException) { MismatchedTokenException mte = (MismatchedTokenException)e; string tokenName = "<unknown>"; if (mte.Expecting == TokenTypes.EndOfFile) { tokenName = "EndOfFile"; } else { tokenName = tokenNames[mte.Expecting]; } msg = "mismatched input " + GetTokenErrorDisplay(e.Token) + " expecting " + tokenName; } else if (e is MismatchedTreeNodeException) { MismatchedTreeNodeException mtne = (MismatchedTreeNodeException)e; string tokenName = "<unknown>"; if (mtne.Expecting == TokenTypes.EndOfFile) { tokenName = "EndOfFile"; } else { tokenName = tokenNames[mtne.Expecting]; } // workaround for a .NET framework bug (NullReferenceException) string nodeText = (mtne.Node != null) ? mtne.Node.ToString() ?? string.Empty : string.Empty; msg = "mismatched tree node: " + nodeText + " expecting " + tokenName; } else if (e is NoViableAltException) { //NoViableAltException nvae = (NoViableAltException)e; // for development, can add "decision=<<"+nvae.grammarDecisionDescription+">>" // and "(decision="+nvae.decisionNumber+") and // "state "+nvae.stateNumber msg = "no viable alternative at input " + GetTokenErrorDisplay(e.Token); } else if (e is EarlyExitException) { //EarlyExitException eee = (EarlyExitException)e; // for development, can add "(decision="+eee.decisionNumber+")" msg = "required (...)+ loop did not match anything at input " + GetTokenErrorDisplay(e.Token); } else if (e is MismatchedSetException) { MismatchedSetException mse = (MismatchedSetException)e; msg = "mismatched input " + GetTokenErrorDisplay(e.Token) + " expecting set " + mse.Expecting; } else if (e is MismatchedNotSetException) { MismatchedNotSetException mse = (MismatchedNotSetException)e; msg = "mismatched input " + GetTokenErrorDisplay(e.Token) + " expecting set " + mse.Expecting; } else if (e is FailedPredicateException) { FailedPredicateException fpe = (FailedPredicateException)e; msg = "rule " + fpe.RuleName + " failed predicate: {" + fpe.PredicateText + "}?"; } return(msg); }