/** <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);
}