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

55 lines
1.3 KiB
JavaScript

"use strict";
let GrammarError = require("../../grammar-error");
let asts = require("../asts");
let 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) {
let visitedRules = [];
let check = visitor.build({
rule(node) {
visitedRules.push(node.name);
check(node.expression);
visitedRules.pop(node.name);
},
sequence(node) {
node.elements.every(element => {
check(element);
return !asts.alwaysConsumesOnSuccess(ast, element);
});
},
rule_ref(node) {
if (visitedRules.indexOf(node.name) !== -1) {
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;