1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
/* 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
|
