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Add support for error recovery.
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@zaach
zaach committed Apr 9, 2010
1 parent a839bf2 commit 4d61450
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Showing 4 changed files with 253 additions and 26 deletions.
127 changes: 102 additions & 25 deletions lib/jison.js
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Expand Up @@ -152,10 +152,10 @@ generator.augmentGrammar = function augmentGrammar (grammar) {
this.productions.unshift(acceptProduction);

// prepend parser tokens
this.symbols.unshift("$accept","$end");
this.symbols.unshift("$accept",this.EOF);
this.symbols_["$accept"] = 0;
this.symbols_["$end"] = 1;
this.terminals.unshift("$end");
this.symbols_[this.EOF] = 1;
this.terminals.unshift(this.EOF);

this.nonterminals["$accept"] = new Nonterminal("$accept");
this.nonterminals["$accept"].productions.push(acceptProduction);
Expand Down Expand Up @@ -184,13 +184,18 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
var symbolId = 1;
var symbols_ = {};

var her = false; // has error recovery

function addSymbol (s) {
if (s && !symbols_[s]) {
symbols_[s] = ++symbolId;
symbols.push(s);
}
}

// add error symbol; will be third symbol, or "2" ($accept, $end, error)
addSymbol("error");

for (symbol in bnf) {
if (!bnf.hasOwnProperty(symbol)) continue;

Expand All @@ -211,7 +216,7 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
else
rhs = handle[0].slice(0);

for (i=0; i<rhs.length; i++) if (!symbols_[rhs[i]]) {
for (i=0; her = her || rhs[i] === 'error',i<rhs.length; i++) if (!symbols_[rhs[i]]) {
addSymbol(rhs[i]);
}

Expand Down Expand Up @@ -252,7 +257,7 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
}
} else {
rhs = handle.trim().split(' ');
for (i=0; i<rhs.length; i++) if (!symbols_[rhs[i]]) {
for (i=0; her = her || rhs[i] === 'error',i<rhs.length; i++) if (!symbols_[rhs[i]]) {
addSymbol(rhs[i]);
}
r = new Production(symbol, rhs, productions.length+1);
Expand Down Expand Up @@ -280,6 +285,8 @@ generator.buildProductions = function buildProductions(bnf, productions, nonterm
}
});

this.hasErrorRecovery = her;

this.terminals = terms;
this.terminals_ = terms_;
this.symbols_ = symbols_;
Expand Down Expand Up @@ -861,14 +868,14 @@ lrGeneratorMixin.generateModule = function generateModule (opt) {
lrGeneratorMixin.generateModule_ = function generateModule_ () {
var out = "{";
out += [
"trace: " + String(this.trace),
"trace: " + String(this.trace || parser.trace),
"yy: {}",
"symbols_: " + JSON.stringify(this.symbols_),
"terminals_: " + JSON.stringify(this.terminals_),
"productions_: " + JSON.stringify(this.productions_),
"performAction: " + String(this.performAction),
"table: " + JSON.stringify(this.table),
"parseError: " + String(this.parseError || parser.parseError),
"parseError: " + String(this.parseError || this.hasErrorRecovery ? traceParseError : parser.parseError),
"parse: " + String(parser.parse)
].join(",\n");
out += "};";
Expand All @@ -882,7 +889,7 @@ function commonjsMain (args) {
if (!args[1])
throw new Error('Usage: '+args[0]+' FILE');
var source = cwd.join(args[1]).read({charset: "utf-8"});
this.parse(source);
exports.parser.parse(source);
}

// debug mixin for LR parser generators
Expand Down Expand Up @@ -935,6 +942,11 @@ lrGeneratorMixin.createParser = function createParser () {
performAction: this.performAction
});

// don't throw if grammar recovers from errors
if (this.hasErrorRecovery) {
p.parseError = traceParseError;
}

// for debugging
p.productions = this.productions;

Expand All @@ -952,6 +964,10 @@ parser.trace = generator.trace;
parser.warn = generator.warn;
parser.error = generator.error;

function traceParseError (err, hash) {
this.trace(err);
}

parser.parseError = lrGeneratorMixin.parseError = function parseError (str, hash) {
throw new Error(str);
};
Expand All @@ -965,12 +981,29 @@ parser.parse = function parse (input) {
yylineno = 0,
yyleng = 0,
shifts = 0,
reductions = 0;
reductions = 0,
recovering = 0,
TERROR = 2,
EOF = 1;

this.lexer.setInput(input);
this.lexer.yy = this.yy;
this.yy.lexer = this.lexer;

var parseError = this.yy.parseError = this.yy.parseError || this.parseError;
var parseError = this.yy.parseError = typeof this.yy.parseError == 'function' ? this.yy.parseError : this.parseError;

function popStack (n) {
stack.length = stack.length - 2*n;
vstack.length = vstack.length - n;
}

function checkRecover (st) {
for (var p in table[st]) if (p == TERROR) {
//print('RECOVER!!');
return true;
}
return false;
}

function lex() {
var token;
Expand All @@ -982,26 +1015,63 @@ parser.parse = function parse (input) {
return token;
};

var symbol, state, action, a, r, yyval={},p,len,ip=0,newState, expected;
var symbol, preErrorSymbol, state, action, a, r, yyval={},p,len,newState, expected, recovered = false;
symbol = lex();
while (true) {
// set first input
state = stack[stack.length-1];
// read action for current state and first input
action = table[state] && table[state][symbol];

// handle parse error
if (typeof action === 'undefined' || !action.length || !action[0]) {
expected = [];
for (p in table[state]) if (this.terminals_[p] && p != 1) {
expected.push("'"+this.terminals_[p]+"'");

if (!recovering) {
// Report error
expected = [];
for (p in table[state]) if (this.terminals_[p] && p > 2) {
expected.push("'"+this.terminals_[p]+"'");
}
if (this.lexer.showPosition) {
parseError.call(this, 'Parse error on line '+(yylineno+1)+":\n"+this.lexer.showPosition()+'\nExpecting '+expected.join(', '),
{text: this.lexer.match, token: this.terminals_[symbol] || symbol, line: this.lexer.yylineno, expected: expected});
} else {
parseError.call(this, 'Parse error on line '+(yylineno+1)+": Unexpected '"+this.terminals_[symbol]+"'",
{text: this.lexer.match, token: this.terminals_[symbol] || symbol, line: this.lexer.yylineno, expected: expected});
}
}
if (this.lexer.showPosition) {
parseError('Parse error on line '+(yylineno+1)+":\n"+this.lexer.showPosition()+'\nExpecting '+expected.join(', '),
{text: this.lexer.match, token: this.terminals_[symbol], line: this.lexer.yylineno, expected: expected});
} else {
parseError('Parse error on line '+(yylineno+1)+": Unexpected '"+this.terminals_[symbol]+"'",
{text: this.lexer.match, token: this.terminals_[symbol], line: this.lexer.yylineno, expected: expected});

// just recovered from another error
if (recovering == 3) {
if (symbol == EOF) {
throw 'Parsing halted.'
}

// discard current lookahead and grab another
yyleng = this.lexer.yyleng;
yytext = this.lexer.yytext;
yylineno = this.lexer.yylineno;
symbol = lex();
}

// try to recover from error
while (1) {
// check for error recovery rule in this state
if (checkRecover(state)) {
break;
}
if (state == 0) {
throw 'Parsing halted.'
}
popStack(1);
state = stack[stack.length-1];
}

preErrorSymbol = symbol; // save the lookahead token
symbol = TERROR; // insert generic error symbol as new lookahead
state = stack[stack.length-1];
action = table[state] && table[state][TERROR];
recovering = 3; // allow 3 real symbols to be shifted before reporting a new error
}

// this shouldn't happen, unless resolve defaults are off
Expand All @@ -1016,13 +1086,20 @@ parser.parse = function parse (input) {
case 1: // shift
shifts++;

stack.push(symbol);++ip;
yyleng = this.lexer.yyleng;
yytext = this.lexer.yytext;
yylineno = this.lexer.yylineno;
symbol = lex();
stack.push(symbol);
vstack.push(null); // semantic values or junk only, no terminals
stack.push(a[1]); // push state
if (!preErrorSymbol) { // normal execution/no error
yyleng = this.lexer.yyleng;
yytext = this.lexer.yytext;
yylineno = this.lexer.yylineno;
symbol = lex();
if (recovering > 0)
recovering--;
} else { // error just occurred, resume old lookahead f/ before error
symbol = preErrorSymbol;
preErrorSymbol = null;
}
break;

case 2: // reduce
Expand Down
3 changes: 2 additions & 1 deletion tests/parser/api.js
View file
Expand Up @@ -111,7 +111,7 @@ exports["test token list as string"] = function () {
};

var gen = new Jison.Generator(grammar);
assert.deepEqual(gen.terminals, ["$end", "x", "y"]);
assert.ok(gen.terminals.indexOf('x') >= 0);
};

exports["test grammar options"] = function () {
Expand Down Expand Up @@ -254,3 +254,4 @@ exports["test no default resolve"] = function () {
assert["throws"](function () {parser.parse("xx")}, "throws parse error for multiple actions");
};


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