Upgrade typescript version

[fa93hws]

Latest version typescript has more strict type check.

[andrewbranch]

Yeah, I don't think the loop is really worth it. Personally I’d probably go with something like

function addCache(servicesHost: typescript.ModuleResolutionHost): {
  moduleResolutionHost: typescript.ModuleResolutionHost,
  clearCache: () => void,
} {
  const clearCacheFunctions: Action[] = [];
  return {
    moduleResolutionHost: {
      ...servicesHost,
      fileExists: createCache(servicesHost.fileExists),
      directoryExists: servicesHost.directoryExists && createCache(servicesHost.directoryExists),
      realpath: servicesHost.realpath && createCache(servicesHost.realpath),
    },
    clearCache: () => clearCacheFunctions.forEach(clear => clear()),
  };

  function createCache<TOut>(originalFunction: (arg: string) => TOut) {
    const cache = new Map<string, TOut>();
    clearCacheFunctions.push(() => cache.clear());
    return function getCached(arg: string) {
      let res = cache.get(arg);
      if (res !== undefined) {
        return res;
      }

      res = originalFunction(arg);
      cache.set(arg, res);
      return res;
    };
  }
}

and then at the usage site

  let clearCache: null | (() => void) = null;
  let moduleResolutionHost: ModuleResolutionHost = {
    fileExists,
    readFile: readFileWithFallback,
    realpath: compiler.sys.realpath,
    directoryExists: compiler.sys.directoryExists,
    getCurrentDirectory: compiler.sys.getCurrentDirectory,
    getDirectories: compiler.sys.getDirectories
  };

  if (enableFileCaching) {
    const cached = addCache(moduleResolutionHost);
    clearCache = cached.clearCache;
    moduleResolutionHost = cached.moduleResolutionHost;
  }

I guess that’s slightly more wordy than what’s proposed here, but doesn’t contain any unsafe type assertions.

[johnnyreilly]

Thanks for the suggestion @andrewbranch!

@fa93hws do you fancy tweaking your PR with the suggested implementation?

[andrewbranch]

I feel like I should add that there are of course lots of different solutions that largely come down to personal preference of coding style. Avoiding unnecessary type assertions is a worthwhile goal, but I’m sure mine is not the most elegant possible solution.

[fa93hws]

No problem!

[johnnyreilly]

Looks good! Do you want to update the CHANGELOG.md? Remember to thank yourself 😁

[johnnyreilly]

Shall we go for TypeScript 3.5.2 since it's out?

[fa93hws]

No problem!
The version goes so quick

[johnnyreilly]

Thanks!