Predicated configs suppress reportAmbiguity

[sharwell]

Currently, no call to reportAmbiguity occurs when one or more ATNConfig instances have a semantic context. This is particularly problematic in tracking down issues in LR rules due to the automatically inserted predicates. One way to resolve this is having ParserATNSimulator.evalSemanticContext return an IntervalSet of all passing alternatives (unpredicated or having a predicate returning true). If the set contains more than one alternative, reportAmbiguity can be called before resolving the set to a single chosen alternative.

This presents a potential problem due to the fact that resolution currently prefers the minimum passing predicated alternative as opposed to the standard minimum acceptable alternative. However, this resolution policy will have to be changed to minimum acceptable alternative to resolve #29.

[parrt]

Yeah, we should essentially gate out all untrue predicated alts and choose min of remaining.

For this issue, we can maybe make an option.

[sharwell]

Fully identifying ambiguities is more work than decision making. In plain decision making mode, adaptivePredict could simply identify the first alt which has a passing config (unpredicated or predicated evaluating to true). In ambiguity detection mode, it would have to check each alternative to try and find at least one passing config, and then call reportAmbiguity if 2 or more alts remain. The ambiguity detection mode may result in more work, but the returned decision will be the same.

[sharwell]

Fixed in 2cc39c2