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* @license Apache-2.0
*
* Copyright (c) 2019 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var parse = require( 'acorn' ).parse;
var walk = require( 'acorn-walk' );
var noop = require( '@stdlib/utils/noop' );
var objectKeys = require( '@stdlib/utils/keys' );
var isSilentCommand = require( './is_silent_command.js' );
// VARIABLES //
var VISITORS = createVisitors({
'ClassDeclaration': ClassDeclaration,
'ForOfStatement': ForOfStatement,
'FunctionDeclaration': FunctionDeclaration,
'FunctionExpression': noop,
'ArrowFunctionExpression': noop,
'MethodDefinition': noop,
'AwaitExpression': AwaitExpression,
'ReturnStatement': ReturnStatement,
'VariableDeclaration': VariableDeclaration
});
// FUNCTIONS //
/**
* Returns an object containing visitor callbacks for recursively walking an abstract syntax tree (AST).
*
* @private
* @param {Object} visitors - visitor callbacks (overrides)
* @returns {Object} object containing visitor callbacks
*/
function createVisitors( visitors ) {
var clbk;
var type;
var keys;
var out;
var i;
keys = objectKeys( walk.base );
out = {};
for ( i = 0; i < keys.length; i++ ) {
type = keys[ i ];
clbk = visitors[ type ] || walk.base[ type ];
out[ type ] = wrapVisitor( clbk );
}
return out;
/**
* Returns a visitor callback which tracks ancestor nodes.
*
* @private
* @param {Function} clbk - callback function
* @returns {Function} visitor callback
*/
function wrapVisitor( clbk ) {
return visitor;
/**
* Callback invoked upon encountering an AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} c - callback
*/
function visitor( node, state, c ) {
var FLG = ( node !== state.ancestors[ state.ancestors.length-1 ] );
if ( FLG ) {
state.ancestors.push( node );
}
clbk( node, state, c ); // eslint-disable-line node/callback-return
if ( FLG ) {
state.ancestors.pop();
}
}
}
}
/**
* Callback invoked upon encountering a `ClassDeclaration` AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function ClassDeclaration( node, state, clbk ) {
if ( state.ancestors[ state.ancestors.length-2 ] === state.body ) {
state.prepend( node, 'global.'+node.id.name+'=' );
}
walk.base.ClassDeclaration( node, state, clbk ); // eslint-disable-line new-cap
}
/**
* Callback invoked upon encountering a `ForOfStatement` AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function ForOfStatement( node, state, clbk ) {
if ( node.await === true ) {
state.hasAwait = true;
}
walk.base.ForOfStatement( node, state, clbk ); // eslint-disable-line new-cap
}
/**
* Callback invoked upon encountering a `FunctionDeclaration` AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function FunctionDeclaration( node, state ) {
state.prepend( node, 'global.'+node.id.name+'=' );
}
/**
* Callback invoked upon encountering an `AwaitExpression` AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function AwaitExpression( node, state, clbk ) {
state.hasAwait = true;
walk.base.AwaitExpression( node, state, clbk ); // eslint-disable-line new-cap
}
/**
* Callback invoked upon encountering a `ReturnStatement` AST node.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function ReturnStatement( node, state, clbk ) {
state.hasReturn = true;
walk.base.ReturnStatement( node, state, clbk ); // eslint-disable-line new-cap
}
/**
* Callback invoked upon encountering a `VariableDeclaration` AST node.
*
* ## Notes
*
* - **WARNING**: top-level `const` declarations are converted to `var` declarations. Unfortunately, as the declarations occur within an `async` function scope, we cannot simultaneously declare the constant in the global scope and bind the resolved value, as the former happens synchronously and the latter asynchronously.
*
* @private
* @param {Node} node - AST node
* @param {Object} state - state
* @param {Function} clbk - callback
*/
function VariableDeclaration( node, state, clbk ) {
var len;
var v;
var i;
if ( node.kind === 'var' || state.ancestors[ state.ancestors.length-2 ] === state.body ) {
len = node.declarations.length;
if ( len === 1 ) {
state.replace( node.start, node.start+node.kind.length, 'void' );
} else {
state.replace( node.start, node.start+node.kind.length, 'void (' );
}
for ( i = 0; i < len; i++ ) {
v = node.declarations[ i ];
state.prepend( v, '(global.' );
state.append( v, ( v.init ) ? ')' : '=void 0)' );
}
if ( len !== 1 ) {
state.append( node.declarations[ len-1 ], ')' );
}
}
walk.base.VariableDeclaration( node, state, clbk ); // eslint-disable-line new-cap
}
/**
* Wraps an `async`/`await` command string in order to handle the result of the returned promise.
*
* @private
* @param {string} cmd - command to wrap
* @returns {string} wrapped command
*/
function wrapCommand( cmd ) {
return [
'"async";',
'(function __iife__() {',
'function __onResult__(result) {__done__(null, result);};',
'function __onError__(error) {__done__(error);};',
'var __p__ = '+cmd+';',
'__p__.then(__onResult__, __onError__);',
'})()'
].join( '' );
}
// MAIN //
/**
* Transforms a command containing a top-level `await` statement.
*
* @private
* @param {string} cmd - command string
* @returns {(string|Error)} transformed command or an error
*/
function processAwait( cmd ) {
var state;
var body;
var node;
var tmp;
var ast;
// Wrap the command string in an async IIFE:
tmp = '(async function __wrapper__() {' + cmd + '})()';
// Attempt to parse the wrapped command string into an abstract syntax tree (AST):
try {
ast = parse( tmp, {
'ecmaVersion': 'latest' // async/await is available starting in ECMAScript Version 10 and acorn supports through version 11 (2020)
});
} catch ( err ) {
return err;
}
body = ast.body[ 0 ].expression.callee.body;
// Split the wrapped command string into individual characters to allow transformation:
tmp = tmp.split( '' );
// Create a `state` object for tracking state as we walk the AST:
state = {};
state.body = body;
state.ancestors = [];
state.replace = replace;
state.prepend = prepend;
state.append = append;
state.hasAwait = false;
state.hasReturn = false;
// Perform a recursive walk of the AST:
walk.recursive( body, state, VISITORS );
// Do not transform if either the command does not actually contain an `await` expression OR if there exists a top-level `return` which is not allowed:
if ( state.hasAwait === false || state.hasReturn ) {
return new Error( 'invalid argument. Provided command either does not contain an `await` expression or contains a top-level `return` which is not allowed.' );
}
// For an expression statement of the form `( expr );`, we do not want the left parenthesis before the `return` keyword, and, thus, we need to prepend a `return (` to the last AST node. Furthermore, we do not want the right parenthesis after the semicolon; in which case, as there can only be more right parentheses between `node.expression.end` and the semicolon, we can append a right parenthesis to `node.expression`.
node = body.body[ body.body.length-1 ];
if ( node.type === 'ExpressionStatement' ) {
state.prepend( node, 'return (' );
state.append( node.expression, ')' );
} else if ( node.type === 'VariableDeclaration' ) {
node = node.declarations[ node.declarations.length-1 ];
state.append( node, '; return '+node.id.name+';' ); // return the assigned value of last declared variable
} else if ( node.type === 'FunctionDeclaration' ) {
state.append( node, '; return '+node.id.name+';' );
}
// Introduce logic for handling the result of the returned promise:
tmp = wrapCommand( tmp.join( '' ) );
if ( isSilentCommand( cmd ) ) {
tmp += ';';
}
// Return the transformed command:
return tmp;
/**
* Replaces a substring within the wrapped command.
*
* @private
* @param {NonNegativeInteger} start - start index
* @param {NonNegativeInteger} stop - end index
* @param {string} str - replacement string
*/
function replace( start, stop, str ) {
var i;
for ( i = start; i < stop; i++ ) {
tmp[ i ] = '';
}
if ( start === stop ) {
str += tmp[ start ];
}
tmp[ start ] = str;
}
/**
* Prepends a string to the wrapped command.
*
* @private
* @param {Node} node - AST node
* @param {string} str - string to prepend
*/
function prepend( node, str ) {
tmp[ node.start ] = str + tmp[ node.start ];
}
/**
* Appends a string to the wrapped command.
*
* @private
* @param {Node} node - AST node
* @param {string} str - string to append
*/
function append( node, str ) {
tmp[ node.end-1] += str;
}
}
// EXPORTS //
module.exports = processAwait;
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