You cannot select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
pegjs/lib/compiler/passes/report-infinite-recursion.js

58 lines
1.4 KiB
JavaScript

"use strict";
var arrays = require("../../utils/arrays"),
GrammarError = require("../../grammar-error"),
asts = require("../asts"),
visitor = require("../visitor");
/*
* Reports left recursion in the grammar, which prevents infinite recursion in
* the generated parser.
*
* Both direct and indirect recursion is detected. The pass also correctly
* reports cases like this:
*
* start = "a"? start
*
* In general, if a rule reference can be reached without consuming any input,
* it can lead to left recursion.
*/
function reportInfiniteRecursion(ast) {
var visitedRules = [];
var check = visitor.build({
rule: function(node) {
visitedRules.push(node.name);
check(node.expression);
visitedRules.pop(node.name);
},
sequence: function(node) {
arrays.every(node.elements, function(element) {
check(element);
return !asts.alwaysConsumesOnSuccess(ast, element);
});
},
rule_ref: function(node) {
if (arrays.contains(visitedRules, node.name)) {
visitedRules.push(node.name);
throw new GrammarError(
"Possible infinite loop when parsing (left recursion: "
+ visitedRules.join(" -> ")
+ ").",
node.location
);
}
check(asts.findRule(ast, node.name));
}
});
check(ast);
}
module.exports = reportInfiniteRecursion;