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