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/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
#pragma once
#include "Parser.h"
#include "atn/ATN.h"
#include "support/BitSet.h"
#include "atn/PredictionContext.h"
#include "atn/PredictionContextCache.h"
#include "Vocabulary.h"
namespace antlr4 {
/// <summary>
/// A parser simulator that mimics what ANTLR's generated
/// parser code does. A ParserATNSimulator is used to make
/// predictions via adaptivePredict but this class moves a pointer through the
/// ATN to simulate parsing. ParserATNSimulator just
/// makes us efficient rather than having to backtrack, for example.
///
/// This properly creates parse trees even for left recursive rules.
///
/// We rely on the left recursive rule invocation and special predicate
/// transitions to make left recursive rules work.
///
/// See TestParserInterpreter for examples.
/// </summary>
class ANTLR4CPP_PUBLIC ParserInterpreter : public Parser {
public:
ParserInterpreter(const std::string &grammarFileName, const dfa::Vocabulary &vocabulary,
const std::vector<std::string> &ruleNames, const atn::ATN &atn, TokenStream *input);
~ParserInterpreter();
virtual void reset() override;
virtual const atn::ATN& getATN() const override;
virtual const dfa::Vocabulary& getVocabulary() const override;
virtual const std::vector<std::string>& getRuleNames() const override;
virtual std::string getGrammarFileName() const override;
/// Begin parsing at startRuleIndex
virtual ParserRuleContext* parse(size_t startRuleIndex);
virtual void enterRecursionRule(ParserRuleContext *localctx, size_t state, size_t ruleIndex, int precedence) override;
/** Override this parser interpreters normal decision-making process
* at a particular decision and input token index. Instead of
* allowing the adaptive prediction mechanism to choose the
* first alternative within a block that leads to a successful parse,
* force it to take the alternative, 1..n for n alternatives.
*
* As an implementation limitation right now, you can only specify one
* override. This is sufficient to allow construction of different
* parse trees for ambiguous input. It means re-parsing the entire input
* in general because you're never sure where an ambiguous sequence would
* live in the various parse trees. For example, in one interpretation,
* an ambiguous input sequence would be matched completely in expression
* but in another it could match all the way back to the root.
*
* s : e '!'? ;
* e : ID
* | ID '!'
* ;
*
* Here, x! can be matched as (s (e ID) !) or (s (e ID !)). In the first
* case, the ambiguous sequence is fully contained only by the root.
* In the second case, the ambiguous sequences fully contained within just
* e, as in: (e ID !).
*
* Rather than trying to optimize this and make
* some intelligent decisions for optimization purposes, I settled on
* just re-parsing the whole input and then using
* {link Trees#getRootOfSubtreeEnclosingRegion} to find the minimal
* subtree that contains the ambiguous sequence. I originally tried to
* record the call stack at the point the parser detected and ambiguity but
* left recursive rules create a parse tree stack that does not reflect
* the actual call stack. That impedance mismatch was enough to make
* it it challenging to restart the parser at a deeply nested rule
* invocation.
*
* Only parser interpreters can override decisions so as to avoid inserting
* override checking code in the critical ALL(*) prediction execution path.
*
* @since 4.5.1
*/
void addDecisionOverride(int decision, int tokenIndex, int forcedAlt);
Ref<InterpreterRuleContext> getOverrideDecisionRoot() const;
/** Return the root of the parse, which can be useful if the parser
* bails out. You still can access the top node. Note that,
* because of the way left recursive rules add children, it's possible
* that the root will not have any children if the start rule immediately
* called and left recursive rule that fails.
*
* @since 4.5.1
*/
InterpreterRuleContext* getRootContext();
protected:
const std::string _grammarFileName;
const atn::ATN &_atn;
std::vector<std::string> _ruleNames;
std::vector<dfa::DFA> _decisionToDFA; // not shared like it is for generated parsers
atn::PredictionContextCache _sharedContextCache;
/** This stack corresponds to the _parentctx, _parentState pair of locals
* that would exist on call stack frames with a recursive descent parser;
* in the generated function for a left-recursive rule you'd see:
*
* private EContext e(int _p) throws RecognitionException {
* ParserRuleContext _parentctx = _ctx; // Pair.a
* int _parentState = getState(); // Pair.b
* ...
* }
*
* Those values are used to create new recursive rule invocation contexts
* associated with left operand of an alt like "expr '*' expr".
*/
std::stack<std::pair<ParserRuleContext *, size_t>> _parentContextStack;
/** We need a map from (decision,inputIndex)->forced alt for computing ambiguous
* parse trees. For now, we allow exactly one override.
*/
int _overrideDecision = -1;
size_t _overrideDecisionInputIndex = INVALID_INDEX;
size_t _overrideDecisionAlt = INVALID_INDEX;
bool _overrideDecisionReached = false; // latch and only override once; error might trigger infinite loop
/** What is the current context when we override a decision? This tells
* us what the root of the parse tree is when using override
* for an ambiguity/lookahead check.
*/
Ref<InterpreterRuleContext> _overrideDecisionRoot;
InterpreterRuleContext* _rootContext;
virtual atn::ATNState *getATNState();
virtual void visitState(atn::ATNState *p);
/** Method visitDecisionState() is called when the interpreter reaches
* a decision state (instance of DecisionState). It gives an opportunity
* for subclasses to track interesting things.
*/
size_t visitDecisionState(atn::DecisionState *p);
/** Provide simple "factory" for InterpreterRuleContext's.
* @since 4.5.1
*/
InterpreterRuleContext* createInterpreterRuleContext(ParserRuleContext *parent, size_t invokingStateNumber, size_t ruleIndex);
virtual void visitRuleStopState(atn::ATNState *p);
/** Rely on the error handler for this parser but, if no tokens are consumed
* to recover, add an error node. Otherwise, nothing is seen in the parse
* tree.
*/
void recover(RecognitionException &e);
Token* recoverInline();
private:
const dfa::Vocabulary &_vocabulary;
std::unique_ptr<Token> _errorToken;
};
} // namespace antlr4