[antlr-interest] Failed Predicate Infinite Loop

[Mark Mandel]

Hey guys,

My grammar can be seen here:
http://coldspring.git.sourceforge.net/git/gitweb.cgi?p=coldspring/coldspring;a=blob;f=antlr/com/coldspring/aop/expression/AopExpression.g;h=b80ef8a7ddd854458791e4e044a8f09461b66c50;hb=HEAD

It's a parser for a subset of AspectJ expressions, with some minor
modifications (if anyone cares ;o) ).

An example expression would be:
@annotation(dostuff='true')

I've used predicate in my lexer to work pick up the first item in the
expression, i.e. an expression should always start with 'target', '@target',
'execution', 'within' or '@annotation'

If I have a typo in the expression that is being entered, e.g.

@annotaion(dostuff='true')

I get the following output:
line 1:7 mismatched character 'i' expecting 't'
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
line 1:8 rule DESCRIPTOR failed predicate: {expressionStart}?
.... (infinite loop) ....

The errors are perfectly correct, but the infinite loop is a bit of a
problem, as I'm sure you can understand.

Is this a bug in ANTLR, or is there a way I can fix/change my grammar (or
add in some custom code), so that I don't fall into the infinite loop? (or
escape out of it)

I'm guessing this is because ANTLR tries to recover from an error whenever
it encounters one. (Which I would also be happy to turn off, I only need the
1st error for my purposes at the moment).

Any help would be appreciated.

Mark


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