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65 lines
1.4 KiB
JavaScript
65 lines
1.4 KiB
JavaScript
"use strict";
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const GrammarError = require( "../../grammar-error" );
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const visitor = require( "../visitor" );
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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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function reportInfiniteRecursion( ast ) {
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const visitedRules = [];
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const check = visitor.build( {
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rule( 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( node ) {
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node.elements.every( element => {
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check( element );
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return ! ast.alwaysConsumesOnSuccess( element );
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} );
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},
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rule_ref( node ) {
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if ( visitedRules.indexOf( node.name ) !== -1 ) {
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visitedRules.push( node.name );
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const rulePath = visitedRules.join( " -> " );
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throw new GrammarError(
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`Possible infinite loop when parsing (left recursion: ${ rulePath }).`,
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node.location
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);
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}
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check( ast.findRule( 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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