78 lines
2.4 KiB
JavaScript
78 lines
2.4 KiB
JavaScript
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'use strict';
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var getFieldAsFn = require('./get-field-as-fn');
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/**
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* Create a decoder for input sources using the given codec hash
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* @this {object} A loader or compilation
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* @param {Array.<object>} codecs A list of codecs, each with a `decode` function
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* @param {boolean} mustDecode Return an error for a source that is not decoded
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* @returns {function(string):string|Error} A decode function that returns an absolute path or else an Error
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*/
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function decodeSourcesWith(codecs, mustDecode) {
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/* jshint validthis:true */
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var context = this;
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// get a list of valid decoders
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var candidates = [].concat(codecs)
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.reduce(reduceValidDecoder.bind(null, codecs), []);
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/**
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* Attempt to decode the given source path using the previously supplied codecs
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* @param {string} inputSource A source path from a source map
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* @returns {Error|string|undefined} An absolute path if decoded else an error if encountered else undefined
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*/
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return function decode(inputSource) {
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// attempt all candidates until a match
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for (var i = 0, decoded = null; i < candidates.length && !decoded; i++) {
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// call the decoder
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try {
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decoded = candidates[i].decode.call(context, inputSource);
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}
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catch (exception) {
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return getNamedError(exception);
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}
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// match implies a return value
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if (decoded) {
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// abstract sources cannot be decoded, only validated
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if (candidates[i].abstract) {
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return undefined;
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}
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// non-string implies error
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if (typeof decoded !== 'string') {
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return getNamedError('Decoder returned a truthy value but it is not a string:\n' + decoded);
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}
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// otherwise success
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else {
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return decoded;
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}
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}
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}
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// default is undefined or error
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return mustDecode ? new Error('No viable decoder for source: ' + inputSource) : undefined;
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function getNamedError(details) {
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var name = candidates[i].name || '(unnamed)',
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message = [
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'Decoding with codec: ' + name,
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'Incoming source: ' + inputSource,
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details && (details.stack ? details.stack : details)
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]
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.filter(Boolean)
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.join('\n');
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return new Error(message);
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}
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};
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}
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module.exports = decodeSourcesWith;
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function reduceValidDecoder(reduced, codec) {
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var decoder = getFieldAsFn('decode')(codec);
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return decoder ? reduced.concat(codec) : reduced;
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}
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