/** Override this method so that we can record which alternative
* was taken at each decision point. For non-left recursive rules,
* it's simple. Set decisionStatesThatSetOuterAltNumInContext
* indicates which decision states should set the outer alternative number.
*
* <p>Left recursive rules are much more complicated to deal with:
* there is typically a decision for the primary alternatives and a
* decision to choose between the recursive operator alternatives.
* For example, the following left recursive rule has two primary and 2
* recursive alternatives.</p>
*
* e : e '*' e
| '-' INT
| e '+' e
| ID
| ;
|
* <p>ANTLR rewrites that rule to be</p>
*
* e[int precedence]
* : ('-' INT | ID)
* ( {...}? '*' e[5]
| {...}? '+' e[3]
| )*
| ;
|
*
* <p>So, there are two decisions associated with picking the outermost alt.
* This complicates our tracking significantly. The outermost alternative number
* is a function of the decision (ATN state) within a left recursive rule and the
* predicted alternative coming back from adaptivePredict().</p>
*
* We use stateToAltsMap as a cache to avoid expensive calls to
* getRecursiveOpAlts().
*/
protected override int VisitDecisionState(DecisionState p)
{
int predictedAlt = base.VisitDecisionState(p);
if (p.NumberOfTransitions > 1)
{
// System.out.println("decision "+p.decision+": "+predictedAlt);
if (p.decision == this.overrideDecision &&
this._input.Index == this.overrideDecisionInputIndex)
{
overrideDecisionRoot = (GrammarInterpreterRuleContext)Context;
}
}
GrammarInterpreterRuleContext ctx = (GrammarInterpreterRuleContext)_ctx;
if (decisionStatesThatSetOuterAltNumInContext.Get(p.stateNumber))
{
ctx.OuterAlternative = predictedAlt;
Rule r = g.GetRule(p.ruleIndex);
if (atn.ruleToStartState[r.index].isPrecedenceRule)
{
int[] alts = stateToAltsMap[p.stateNumber];
LeftRecursiveRule lr = (LeftRecursiveRule)g.GetRule(p.ruleIndex);
if (p.StateType == StateType.BlockStart)
{
if (alts == null)
{
alts = lr.GetPrimaryAlts();
stateToAltsMap[p.stateNumber] = alts; // cache it
}
}
else if (p.StateType == StateType.StarBlockStart)
{
if (alts == null)
{
alts = lr.GetRecursiveOpAlts();
stateToAltsMap[p.stateNumber] = alts; // cache it
}
}
ctx.OuterAlternative = alts[predictedAlt];
}
}
return(predictedAlt);
}
/** Given an ambiguous parse information, return the list of ambiguous parse trees.
* An ambiguity occurs when a specific token sequence can be recognized
* in more than one way by the grammar. These ambiguities are detected only
* at decision points.
*
* The list of trees includes the actual interpretation (that for
* the minimum alternative number) and all ambiguous alternatives.
* The actual interpretation is always first.
*
* This method reuses the same physical input token stream used to
* detect the ambiguity by the original parser in the first place.
* This method resets/seeks within but does not alter originalParser.
*
* The trees are rooted at the node whose start..stop token indices
* include the start and stop indices of this ambiguity event. That is,
* the trees returned will always include the complete ambiguous subphrase
* identified by the ambiguity event. The subtrees returned will
* also always contain the node associated with the overridden decision.
*
* Be aware that this method does NOT notify error or parse listeners as
* it would trigger duplicate or otherwise unwanted events.
*
* This uses a temporary ParserATNSimulator and a ParserInterpreter
* so we don't mess up any statistics, event lists, etc...
* The parse tree constructed while identifying/making ambiguityInfo is
* not affected by this method as it creates a new parser interp to
* get the ambiguous interpretations.
*
* Nodes in the returned ambig trees are independent of the original parse
* tree (constructed while identifying/creating ambiguityInfo).
*
* @since 4.5.1
*
* @param g From which grammar should we drive alternative
* numbers and alternative labels.
*
* @param originalParser The parser used to create ambiguityInfo; it
* is not modified by this routine and can be either
* a generated or interpreted parser. It's token
* stream *is* reset/seek()'d.
* @param tokens A stream of tokens to use with the temporary parser.
* This will often be just the token stream within the
* original parser but here it is for flexibility.
*
* @param decision Which decision to try different alternatives for.
*
* @param alts The set of alternatives to try while re-parsing.
*
* @param startIndex The index of the first token of the ambiguous
* input or other input of interest.
*
* @param stopIndex The index of the last token of the ambiguous input.
* The start and stop indexes are used primarily to
* identify how much of the resulting parse tree
* to return.
*
* @param startRuleIndex The start rule for the entire grammar, not
* the ambiguous decision. We re-parse the entire input
* and so we need the original start rule.
*
* @return The list of all possible interpretations of
* the input for the decision in ambiguityInfo.
* The actual interpretation chosen by the parser
* is always given first because this method
* retests the input in alternative order and
* ANTLR always resolves ambiguities by choosing
* the first alternative that matches the input.
* The subtree returned
*
* @throws RecognitionException Throws upon syntax error while matching
* ambig input.
*/
public static IList <ParserRuleContext> GetAllPossibleParseTrees(Grammar g,
Parser originalParser,
ITokenStream tokens,
int decision,
BitSet alts,
int startIndex,
int stopIndex,
int startRuleIndex)
{
IList <ParserRuleContext> trees = new List <ParserRuleContext>();
// Create a new parser interpreter to parse the ambiguous subphrase
ParserInterpreter parser = DeriveTempParserInterpreter(g, originalParser, tokens);
if (stopIndex >= (tokens.Size - 1))
{
// if we are pointing at EOF token
// EOF is not in tree, so must be 1 less than last non-EOF token
stopIndex = tokens.Size - 2;
}
// get ambig trees
int alt = alts.NextSetBit(0);
while (alt >= 0)
{
// re-parse entire input for all ambiguous alternatives
// (don't have to do first as it's been parsed, but do again for simplicity
// using this temp parser.)
parser.Reset();
parser.AddDecisionOverride(decision, startIndex, alt);
ParserRuleContext t = parser.Parse(startRuleIndex);
GrammarInterpreterRuleContext ambigSubTree =
(GrammarInterpreterRuleContext)Trees.GetRootOfSubtreeEnclosingRegion(t, startIndex, stopIndex);
// Use higher of overridden decision tree or tree enclosing all tokens
if (Trees.IsAncestorOf(parser.OverrideDecisionRoot, ambigSubTree))
{
ambigSubTree = (GrammarInterpreterRuleContext)parser.OverrideDecisionRoot;
}
trees.Add(ambigSubTree);
alt = alts.NextSetBit(alt + 1);
}
return(trees);
}
