Ensure module map is only generated once

[ethul]

// map of PS module names to their source path
function psModuleMap(options, cache) {
  if (cache.psModuleMap) return cache.psModuleMap;
  else {
    var globs = [].concat(options.src).concat(options.ffi);

    cache.psModuleMap = globby(globs).then(function (paths) {
      return Promise.props(paths.reduce(function (map, file) {
        map[file] = fs.readFileAsync(file, 'utf8');
        return map;
      }, {})).then(function (fileMap) {
        return Object.keys(fileMap).reduce(function (map, file) {
          var source = fileMap[file];
          var ext = path.extname(file);
          var isPurs = ext.match(/purs$/i);
          var moduleRegex = isPurs ? srcModuleRegex : ffiModuleRegex;
          var moduleName = match(moduleRegex, source);
          map[moduleName] = map[moduleName] || {};
          if (isPurs) {
            map[moduleName].src = path.resolve(file);
          } else {
            map[moduleName].ffi = path.resolve(file);
          }
          return map;
        }, {});
      });
    });

    return cache.psModuleMap;
  }
}

[ethul]

Check if this issue is present in recent versions.

[ethul]

Indeed this issue is present in the latest version:

purs-loader/src/to-javascript.js

Lines 28 to 44 in 4dd301a

	if (!cache.psModuleMap) {
	debug('module mapping does not exist');
	return PsModuleMap.makeMap(options.src).then(map => {
	cache.psModuleMap = map;
	return cache.psModuleMap;
	});
	}
	else {
	return PsModuleMap.makeMapEntry(filePurs).then(result => {
	const map = Object.assign(cache.psModuleMap, result);
	cache.psModuleMap = map;
	return cache.psModuleMap;
	});
	}

purs-loader/src/index.js

Lines 253 to 257 in 466c006

	PsModuleMap.makeMap(options.src).then(map => {
	debug('rebuilt module map after unknown module forced a recompilation');
	cache.psModuleMap = map;
	})

purs-loader/src/index.js

Lines 321 to 325 in 466c006

	PsModuleMap.makeMap(options.src).then(map => {
	debug('rebuilt module map after compilation');
	cache.psModuleMap = map;
	})

We can apply the same style of fix where the module map is set to be a promise.