+ /// the parser instance
+ /// the recognition exception
+ virtual void reportFailedPredicate(Parser *recognizer, const FailedPredicateException &e);
+
+ /**
+ * This method is called to report a syntax error which requires the removal
+ * of a token from the input stream. At the time this method is called, the
+ * erroneous symbol is current {@code LT(1)} symbol and has not yet been
+ * removed from the input stream. When this method returns,
+ * {@code recognizer} is in error recovery mode.
+ *
+ * This method is called when {@link #singleTokenDeletion} identifies
+ * single-token deletion as a viable recovery strategy for a mismatched
+ * input error.
+ *
+ * The default implementation simply returns if the handler is already in
+ * error recovery mode. Otherwise, it calls {@link #beginErrorCondition} to
+ * enter error recovery mode, followed by calling
+ * {@link Parser#notifyErrorListeners}.
+ *
+ * @param recognizer the parser instance
+ */
+ virtual void reportUnwantedToken(Parser *recognizer);
+
+ /**
+ * This method is called to report a syntax error which requires the
+ * insertion of a missing token into the input stream. At the time this
+ * method is called, the missing token has not yet been inserted. When this
+ * method returns, {@code recognizer} is in error recovery mode.
+ *
+ * This method is called when {@link #singleTokenInsertion} identifies
+ * single-token insertion as a viable recovery strategy for a mismatched
+ * input error.
+ *
+ * The default implementation simply returns if the handler is already in
+ * error recovery mode. Otherwise, it calls {@link #beginErrorCondition} to
+ * enter error recovery mode, followed by calling
+ * {@link Parser#notifyErrorListeners}.
+ *
+ * @param recognizer the parser instance
+ */
+ virtual void reportMissingToken(Parser *recognizer);
+
+ public:
+ /**
+ * {@inheritDoc}
+ *
+ * The default implementation attempts to recover from the mismatched input
+ * by using single token insertion and deletion as described below. If the
+ * recovery attempt fails, this method throws an
+ * {@link InputMismatchException}.
+ *
+ * EXTRA TOKEN (single token deletion)
+ *
+ * {@code LA(1)} is not what we are looking for. If {@code LA(2)} has the
+ * right token, however, then assume {@code LA(1)} is some extra spurious
+ * token and delete it. Then consume and return the next token (which was
+ * the {@code LA(2)} token) as the successful result of the match operation.
+ *
+ * This recovery strategy is implemented by {@link #singleTokenDeletion}.
+ *
+ * MISSING TOKEN (single token insertion)
+ *
+ * If current token (at {@code LA(1)}) is consistent with what could come
+ * after the expected {@code LA(1)} token, then assume the token is missing
+ * and use the parser's {@link TokenFactory} to create it on the fly. The
+ * "insertion" is performed by returning the created token as the successful
+ * result of the match operation.
+ *
+ * This recovery strategy is implemented by {@link #singleTokenInsertion}.
+ *
+ * EXAMPLE
+ *
+ * For example, Input {@code i=(3;} is clearly missing the {@code ')'}. When
+ * the parser returns from the nested call to {@code expr}, it will have
+ * call chain:
+ *
+ *
+ * stat → expr → atom
+ *
+ *
+ * and it will be trying to match the {@code ')'} at this point in the
+ * derivation:
+ *
+ *
+ * => ID '=' '(' INT ')' ('+' atom)* ';'
+ * ^
+ *
+ *
+ * The attempt to match {@code ')'} will fail when it sees {@code ';'} and
+ * call {@link #recoverInline}. To recover, it sees that {@code LA(1)==';'}
+ * is in the set of tokens that can follow the {@code ')'} token reference
+ * in rule {@code atom}. It can assume that you forgot the {@code ')'}.
+ */
+ virtual Token* recoverInline(Parser *recognizer) override;
+
+ ///
+ /// This method implements the single-token insertion inline error recovery
+ /// strategy. It is called by if the single-token
+ /// deletion strategy fails to recover from the mismatched input. If this
+ /// method returns {@code true}, {@code recognizer} will be in error recovery
+ /// mode.
+ ///
+ /// This method determines whether or not single-token insertion is viable by
+ /// checking if the {@code LA(1)} input symbol could be successfully matched
+ /// if it were instead the {@code LA(2)} symbol. If this method returns
+ /// {@code true}, the caller is responsible for creating and inserting a
+ /// token with the correct type to produce this behavior.
+ ///
+ /// the parser instance
+ /// {@code true} if single-token insertion is a viable recovery
+ /// strategy for the current mismatched input, otherwise {@code false}
+ protected:
+ virtual bool singleTokenInsertion(Parser *recognizer);
+
+ ///
+ /// This method implements the single-token deletion inline error recovery
+ /// strategy. It is called by to attempt to recover
+ /// from mismatched input. If this method returns null, the parser and error
+ /// handler state will not have changed. If this method returns non-null,
+ /// {@code recognizer} will not be in error recovery mode since the
+ /// returned token was a successful match.
+ ///
+ /// If the single-token deletion is successful, this method calls
+ /// to report the error, followed by
+ /// to actually "delete" the extraneous token. Then,
+ /// before returning is called to signal a successful
+ /// match.
+ ///
+ /// the parser instance
+ /// the successfully matched instance if single-token
+ /// deletion successfully recovers from the mismatched input, otherwise
+ /// {@code null}
+ virtual Token* singleTokenDeletion(Parser *recognizer);
+
+ ///
+ /// Conjure up a missing token during error recovery.
+ ///
+ /// The recognizer attempts to recover from single missing
+ /// symbols. But, actions might refer to that missing symbol.
+ /// For example, x=ID {f($x);}. The action clearly assumes
+ /// that there has been an identifier matched previously and that
+ /// $x points at that token. If that token is missing, but
+ /// the next token in the stream is what we want we assume that
+ /// this token is missing and we keep going. Because we
+ /// have to return some token to replace the missing token,
+ /// we have to conjure one up. This method gives the user control
+ /// over the tokens returned for missing tokens. Mostly,
+ /// you will want to create something special for identifier
+ /// tokens. For literals such as '{' and ',', the default
+ /// action in the parser or tree parser works. It simply creates
+ /// a CommonToken of the appropriate type. The text will be the token.
+ /// If you change what tokens must be created by the lexer,
+ /// override this method to create the appropriate tokens.
+ ///
+ virtual Token* getMissingSymbol(Parser *recognizer);
+
+ virtual misc::IntervalSet getExpectedTokens(Parser *recognizer);
+
+ ///
+ /// How should a token be displayed in an error message? The default
+ /// is to display just the text, but during development you might
+ /// want to have a lot of information spit out. Override in that case
+ /// to use t.toString() (which, for CommonToken, dumps everything about
+ /// the token). This is better than forcing you to override a method in
+ /// your token objects because you don't have to go modify your lexer
+ /// so that it creates a new class.
+ ///
+ virtual std::string getTokenErrorDisplay(Token *t);
+
+ virtual std::string getSymbolText(Token *symbol);
+
+ virtual size_t getSymbolType(Token *symbol);
+
+ virtual std::string escapeWSAndQuote(const std::string &s) const;
+
+ /* Compute the error recovery set for the current rule. During
+ * rule invocation, the parser pushes the set of tokens that can
+ * follow that rule reference on the stack; this amounts to
+ * computing FIRST of what follows the rule reference in the
+ * enclosing rule. See LinearApproximator.FIRST().
+ * This local follow set only includes tokens
+ * from within the rule; i.e., the FIRST computation done by
+ * ANTLR stops at the end of a rule.
+ *
+ * EXAMPLE
+ *
+ * When you find a "no viable alt exception", the input is not
+ * consistent with any of the alternatives for rule r. The best
+ * thing to do is to consume tokens until you see something that
+ * can legally follow a call to r *or* any rule that called r.
+ * You don't want the exact set of viable next tokens because the
+ * input might just be missing a token--you might consume the
+ * rest of the input looking for one of the missing tokens.
+ *
+ * Consider grammar:
+ *
+ * a : '[' b ']'
+ * | '(' b ')'
+ * ;
+ * b : c '^' INT ;
+ * c : ID
+ * | INT
+ * ;
+ *
+ * At each rule invocation, the set of tokens that could follow
+ * that rule is pushed on a stack. Here are the various
+ * context-sensitive follow sets:
+ *
+ * FOLLOW(b1_in_a) = FIRST(']') = ']'
+ * FOLLOW(b2_in_a) = FIRST(')') = ')'
+ * FOLLOW(c_in_b) = FIRST('^') = '^'
+ *
+ * Upon erroneous input "[]", the call chain is
+ *
+ * a -> b -> c
+ *
+ * and, hence, the follow context stack is:
+ *
+ * depth follow set start of rule execution
+ * 0 a (from main())
+ * 1 ']' b
+ * 2 '^' c
+ *
+ * Notice that ')' is not included, because b would have to have
+ * been called from a different context in rule a for ')' to be
+ * included.
+ *
+ * For error recovery, we cannot consider FOLLOW(c)
+ * (context-sensitive or otherwise). We need the combined set of
+ * all context-sensitive FOLLOW sets--the set of all tokens that
+ * could follow any reference in the call chain. We need to
+ * resync to one of those tokens. Note that FOLLOW(c)='^' and if
+ * we resync'd to that token, we'd consume until EOF. We need to
+ * sync to context-sensitive FOLLOWs for a, b, and c: {']','^'}.
+ * In this case, for input "[]", LA(1) is ']' and in the set, so we would
+ * not consume anything. After printing an error, rule c would
+ * return normally. Rule b would not find the required '^' though.
+ * At this point, it gets a mismatched token error and throws an
+ * exception (since LA(1) is not in the viable following token
+ * set). The rule exception handler tries to recover, but finds
+ * the same recovery set and doesn't consume anything. Rule b
+ * exits normally returning to rule a. Now it finds the ']' (and
+ * with the successful match exits errorRecovery mode).
+ *
+ * So, you can see that the parser walks up the call chain looking
+ * for the token that was a member of the recovery set.
+ *
+ * Errors are not generated in errorRecovery mode.
+ *
+ * ANTLR's error recovery mechanism is based upon original ideas:
+ *
+ * "Algorithms + Data Structures = Programs" by Niklaus Wirth
+ *
+ * and
+ *
+ * "A note on error recovery in recursive descent parsers":
+ * http://portal.acm.org/citation.cfm?id=947902.947905
+ *
+ * Later, Josef Grosch had some good ideas:
+ *
+ * "Efficient and Comfortable Error Recovery in Recursive Descent
+ * Parsers":
+ * ftp://www.cocolab.com/products/cocktail/doca4.ps/ell.ps.zip
+ *
+ * Like Grosch I implement context-sensitive FOLLOW sets that are combined
+ * at run-time upon error to avoid overhead during parsing.
+ */
+ virtual misc::IntervalSet getErrorRecoverySet(Parser *recognizer);
+
+ ///
+ /// Consume tokens until one matches the given token set.
+ virtual void consumeUntil(Parser *recognizer, const misc::IntervalSet &set);
+
+ private:
+ std::vector> _errorSymbols; // Temporarily created token.
+ void InitializeInstanceFields();
+ };
+
+} // namespace antlr4