Very slow as soon as "coffescript" package is installed

[neelance]

On our codebase (with a simplified config), depcruiser takes 7 seconds to complete. As soon as the "coffeescript" package is installed, it takes 40 seconds instead.

I understand that automatically using the transpiler if it is installed is an intended feature. However, this performance behaviour is surprising and not easy to debug. It took a while for me to pinpoint "coffeescript" as the culprit.

I see a several options to improve this:

• Print a warning if the CoffeeScript transpiler is used and there are many .js files
• Print a warning if the CoffeeScript transpiler is used and there are no .coffee files
• Do not use the CoffeeScript transpiler if there are no .coffee files
• Make the CoffeeScript transpiler opt-in in the config

[sverweij]

Hi @neelance (sorry for the slow response - private life takes a bit more time than previously at the moment).

I can think of two things within the program that'd explain slower execution with the mere pressence of the coffeescript compiler:

• At start-up time it will try to load the coffeescript compiler. This will make dependency-cruiser's startup time a bit slower (on my local machine it's 10ms). I don't think that's the culprit here.
• During module resolution - dependency-cruiser by default configures the resolver to go through the list of extensions it has a compiler for available, until it finds a hit. If there's a few modules that can't be resolved to disk at all, the resolver will run through the entire list - which will be noticeable in its run time, especially so for coffeescript as it supports a whopping 6 extra extensions to try out. From your description this seems what is happening.
• depcruise --info will show you the compilers dependency-cruiser found as well as the list of extensions it (as a consequence) supports (and hence scans) by default.

A potential fix/ workaround:

With the enhancedResolveOptions.extensions option you can curb this (safe but potentially slow) default behavior by limiting the extensions it scans. This is also what depcruise --init will attempt when it scaffolds a .dependency-cruiser.js - it scans the contents of your source folder and set up the extensions property to those it found there.