Class DiagnosticErrorListener

java.lang.Object
org.antlr.v4.runtime.BaseErrorListener
org.antlr.v4.runtime.DiagnosticErrorListener
All Implemented Interfaces:
ANTLRErrorListener

public class DiagnosticErrorListener extends BaseErrorListener
This implementation of ANTLRErrorListener can be used to identify certain potential correctness and performance problems in grammars. "Reports" are made by calling Parser.notifyErrorListeners(java.lang.String) with the appropriate message.
  • Ambiguities: These are cases where more than one path through the grammar can match the input.
  • Weak context sensitivity: These are cases where full-context prediction resolved an SLL conflict to a unique alternative which equaled the minimum alternative of the SLL conflict.
  • Strong (forced) context sensitivity: These are cases where the full-context prediction resolved an SLL conflict to a unique alternative, and the minimum alternative of the SLL conflict was found to not be a truly viable alternative. Two-stage parsing cannot be used for inputs where this situation occurs.
Author:
Sam Harwell
  • Field Details

    • exactOnly

      protected final boolean exactOnly
      When true, only exactly known ambiguities are reported.
  • Constructor Details

    • DiagnosticErrorListener

      public DiagnosticErrorListener()
      Initializes a new instance of DiagnosticErrorListener which only reports exact ambiguities.
    • DiagnosticErrorListener

      public DiagnosticErrorListener(boolean exactOnly)
      Initializes a new instance of DiagnosticErrorListener, specifying whether all ambiguities or only exact ambiguities are reported.
      Parameters:
      exactOnly - true to report only exact ambiguities, otherwise false to report all ambiguities.
  • Method Details

    • reportAmbiguity

      public void reportAmbiguity(Parser recognizer, DFA dfa, int startIndex, int stopIndex, boolean exact, BitSet ambigAlts, ATNConfigSet configs)
      Description copied from interface: ANTLRErrorListener
      This method is called by the parser when a full-context prediction results in an ambiguity.

      Each full-context prediction which does not result in a syntax error will call either ANTLRErrorListener.reportContextSensitivity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, int, org.antlr.v4.runtime.atn.ATNConfigSet) or ANTLRErrorListener.reportAmbiguity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, boolean, java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet).

      When ambigAlts is not null, it contains the set of potentially viable alternatives identified by the prediction algorithm. When ambigAlts is null, use ATNConfigSet.getAlts() to obtain the represented alternatives from the configs argument.

      When exact is true, all of the potentially viable alternatives are truly viable, i.e. this is reporting an exact ambiguity. When exact is false, at least two of the potentially viable alternatives are viable for the current input, but the prediction algorithm terminated as soon as it determined that at least the minimum potentially viable alternative is truly viable.

      When the PredictionMode.LL_EXACT_AMBIG_DETECTION prediction mode is used, the parser is required to identify exact ambiguities so exact will always be true.

      This method is not used by lexers.

      Specified by:
      reportAmbiguity in interface ANTLRErrorListener
      Overrides:
      reportAmbiguity in class BaseErrorListener
      Parameters:
      recognizer - the parser instance
      dfa - the DFA for the current decision
      startIndex - the input index where the decision started
      stopIndex - the input input where the ambiguity was identified
      exact - true if the ambiguity is exactly known, otherwise false. This is always true when PredictionMode.LL_EXACT_AMBIG_DETECTION is used.
      ambigAlts - the potentially ambiguous alternatives, or null to indicate that the potentially ambiguous alternatives are the complete set of represented alternatives in configs
      configs - the ATN configuration set where the ambiguity was identified
    • reportAttemptingFullContext

      public void reportAttemptingFullContext(Parser recognizer, DFA dfa, int startIndex, int stopIndex, BitSet conflictingAlts, ATNConfigSet configs)
      Description copied from interface: ANTLRErrorListener
      This method is called when an SLL conflict occurs and the parser is about to use the full context information to make an LL decision.

      If one or more configurations in configs contains a semantic predicate, the predicates are evaluated before this method is called. The subset of alternatives which are still viable after predicates are evaluated is reported in conflictingAlts.

      This method is not used by lexers.

      Specified by:
      reportAttemptingFullContext in interface ANTLRErrorListener
      Overrides:
      reportAttemptingFullContext in class BaseErrorListener
      Parameters:
      recognizer - the parser instance
      dfa - the DFA for the current decision
      startIndex - the input index where the decision started
      stopIndex - the input index where the SLL conflict occurred
      conflictingAlts - The specific conflicting alternatives. If this is null, the conflicting alternatives are all alternatives represented in configs. At the moment, conflictingAlts is non-null (for the reference implementation, but Sam's optimized version can see this as null).
      configs - the ATN configuration set where the SLL conflict was detected
    • reportContextSensitivity

      public void reportContextSensitivity(Parser recognizer, DFA dfa, int startIndex, int stopIndex, int prediction, ATNConfigSet configs)
      Description copied from interface: ANTLRErrorListener
      This method is called by the parser when a full-context prediction has a unique result.

      Each full-context prediction which does not result in a syntax error will call either ANTLRErrorListener.reportContextSensitivity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, int, org.antlr.v4.runtime.atn.ATNConfigSet) or ANTLRErrorListener.reportAmbiguity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, boolean, java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet).

      For prediction implementations that only evaluate full-context predictions when an SLL conflict is found (including the default ParserATNSimulator implementation), this method reports cases where SLL conflicts were resolved to unique full-context predictions, i.e. the decision was context-sensitive. This report does not necessarily indicate a problem, and it may appear even in completely unambiguous grammars.

      configs may have more than one represented alternative if the full-context prediction algorithm does not evaluate predicates before beginning the full-context prediction. In all cases, the final prediction is passed as the prediction argument.

      Note that the definition of "context sensitivity" in this method differs from the concept in DecisionInfo.contextSensitivities. This method reports all instances where an SLL conflict occurred but LL parsing produced a unique result, whether or not that unique result matches the minimum alternative in the SLL conflicting set.

      This method is not used by lexers.

      Specified by:
      reportContextSensitivity in interface ANTLRErrorListener
      Overrides:
      reportContextSensitivity in class BaseErrorListener
      Parameters:
      recognizer - the parser instance
      dfa - the DFA for the current decision
      startIndex - the input index where the decision started
      stopIndex - the input index where the context sensitivity was finally determined
      prediction - the unambiguous result of the full-context prediction
      configs - the ATN configuration set where the unambiguous prediction was determined
    • getDecisionDescription

      protected String getDecisionDescription(Parser recognizer, DFA dfa)
    • getConflictingAlts

      protected BitSet getConflictingAlts(BitSet reportedAlts, ATNConfigSet configs)
      Computes the set of conflicting or ambiguous alternatives from a configuration set, if that information was not already provided by the parser.
      Parameters:
      reportedAlts - The set of conflicting or ambiguous alternatives, as reported by the parser.
      configs - The conflicting or ambiguous configuration set.
      Returns:
      Returns reportedAlts if it is not null, otherwise returns the set of alternatives represented in configs.