/** Return a list of parse trees, one for each alternative in a decision
* given the same input.
*
* Very similar to {@link #getAllPossibleParseTrees} except
* that it re-parses the input for every alternative in a decision,
* not just the ambiguous ones (there is no alts parameter here).
* This method also tries to reduce the size of the parse trees
* by stripping away children of the tree that are completely out of range
* of startIndex..stopIndex. Also, because errors are expected, we
* use a specialized error handler that more or less bails out
* but that also consumes the first erroneous token at least. This
* ensures that an error node will be in the parse tree for display.
*
* NOTES:
* // we must parse the entire input now with decision overrides
* // we cannot parse a subset because it could be that a decision
* // above our decision of interest needs to read way past
* // lookaheadInfo.stopIndex. It seems like there is no escaping
* // the use of a full and complete token stream if we are
* // resetting to token index 0 and re-parsing from the start symbol.
* // It's not easy to restart parsing somewhere in the middle like a
* // continuation because our call stack does not match the
* // tree stack because of left recursive rule rewriting. grrrr!
*
* @since 4.5.1
*/
public static IList <ParserRuleContext> GetLookaheadParseTrees(Grammar g,
ParserInterpreter originalParser,
ITokenStream tokens,
int startRuleIndex,
int decision,
int startIndex,
int stopIndex)
{
IList <ParserRuleContext> trees = new List <ParserRuleContext>();
// Create a new parser interpreter to parse the ambiguous subphrase
ParserInterpreter parser = DeriveTempParserInterpreter(g, originalParser, tokens);
DecisionState decisionState = originalParser.Atn.decisionToState[decision];
for (int alt = 1; alt <= decisionState.Transitions.Length; alt++)
{
// 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.)
BailButConsumeErrorStrategy errorHandler = new BailButConsumeErrorStrategy();
parser.ErrorHandler = errorHandler;
parser.Reset();
parser.AddDecisionOverride(decision, startIndex, alt);
ParserRuleContext tt = parser.Parse(startRuleIndex);
int stopTreeAt = stopIndex;
if (errorHandler.firstErrorTokenIndex >= 0)
{
stopTreeAt = errorHandler.firstErrorTokenIndex; // cut off rest at first error
}
Interval overallRange = tt.SourceInterval;
if (stopTreeAt > overallRange.b)
{
// If we try to look beyond range of tree, stopTreeAt must be EOF
// for which there is no EOF ref in grammar. That means tree
// will not have node for stopTreeAt; limit to overallRange.b
stopTreeAt = overallRange.b;
}
ParserRuleContext subtree =
Trees.GetRootOfSubtreeEnclosingRegion(tt,
startIndex,
stopTreeAt);
// Use higher of overridden decision tree or tree enclosing all tokens
if (Trees.IsAncestorOf(parser.OverrideDecisionRoot, subtree))
{
subtree = parser.OverrideDecisionRoot;
}
Trees.StripChildrenOutOfRange(subtree, parser.OverrideDecisionRoot, startIndex, stopTreeAt);
trees.Add(subtree);
}
return(trees);
}
/** 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);
}
