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150 lines
3.3 KiB
JavaScript
150 lines
3.3 KiB
JavaScript
"use strict";
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const util = require( "../util" );
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const __slice = Array.prototype.slice;
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// Abstract syntax tree visitor for PEG.js
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class ASTVisitor {
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// Will traverse the node, strictly assuming the visitor can handle the node type.
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visit( node ) {
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// istanbul ignore next
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if ( ! node ) throw new Error( "Visitor function called with no arguments or a `falsy` node" );
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const fn = this[ node.type ];
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// istanbul ignore next
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if ( ! fn ) throw new Error( `Visitor function for node type "${ node.type }" not defined` );
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return fn.apply( this, arguments );
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}
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}
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module.exports = {
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ASTVisitor,
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// Simple AST node visitor builder for PEG.js
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build( functions ) {
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let visitor = new ASTVisitor();
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util.extend( visitor, functions );
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visitor = util.enforceFastProperties( visitor );
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return visitor.visit.bind( visitor );
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},
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};
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// Helper's to create visitor's for use with the ASTVisitor class
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const on = ASTVisitor.for = {
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// Visit a node that is defined as a property on another node
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property( name ) {
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return function visitProperty( node ) {
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const extraArgs = __slice.call( arguments, 1 );
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const value = node[ name ];
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if ( extraArgs.length )
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this.visit.apply( this, [ value ].concat( extraArgs ) );
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else
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this.visit( value );
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};
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},
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// Visit an array of nodes that are defined as a property on another node
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children( name ) {
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return function visitProperty( node ) {
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const args = __slice.call( arguments, 0 );
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const children = node[ name ];
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const visitor = this;
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const cb = args.length < 2
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? function withoutArgs( child ) {
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visitor.visit( child );
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}
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: function withArgs( child ) {
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args[ 0 ] = child;
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visitor.visit.apply( visitor, args );
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};
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children.forEach( cb );
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};
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},
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};
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// Build the default ast visitor functions
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const visitNop = util.noop;
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const visitExpression = on.property( "expression" );
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const DEFAULT_FUNCTIONS = {
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grammar( node ) {
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const args = [ void 0 ].concat( __slice.call( arguments, 1 ) );
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if ( node.initializer ) {
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args[ 0 ] = node.initializer;
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this.visit.apply( this, args );
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}
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node.rules.forEach( rule => {
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args[ 0 ] = rule;
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this.visit.apply( this, args );
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} );
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},
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initializer: visitNop,
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rule: visitExpression,
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named: visitExpression,
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choice: on.children( "alternatives" ),
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action: visitExpression,
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sequence: on.children( "elements" ),
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labeled: visitExpression,
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text: visitExpression,
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simple_and: visitExpression,
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simple_not: visitExpression,
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optional: visitExpression,
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zero_or_more: visitExpression,
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one_or_more: visitExpression,
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group: visitExpression,
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semantic_and: visitNop,
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semantic_not: visitNop,
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rule_ref: visitNop,
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literal: visitNop,
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class: visitNop,
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any: visitNop,
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};
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util.each( DEFAULT_FUNCTIONS, ( fn, name ) => {
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ASTVisitor.prototype[ name ] = fn;
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} );
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