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.
58 lines
1.4 KiB
JavaScript
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) {
|
|
node.elements.every(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;
|