feat: allow --reporter to be relative to CWD

[elliottsj]

This PR contains a:

• new feature
• test update

Motivation / Use-Case

Previously, the --reporter path must have been either absolute or in node_modules or relative to lib/compiler.js.

This change ensures that a path passed to --reporter is resolved relative to process.cwd().

e.g. you can now run this inside of a project directory to use a custom reporter:

webpack --reporter ./MyCustomReporter.js

Breaking Changes

None

[jsf-clabot]

All committers have signed the CLA.

[shellscape]

Love the idea. But I'm not a fan of the code changes at all. Not saying that to be harsh in the slightest - the refactor can be much, much better. The tests are solid, but the increase in complexity of the code is no bueno.

This block was originally designed to be very simple, and the try/catch approach was pretty basic; one require fails, try another without having the inspect the filesystem, and if all else fails, return null and it'll be handled downstream.

Throwing relative paths in there means that the target can be one of three things:

1. reporter in the package
2. reporter something on the filesystem
3. reporter in node_modules

The very first thing that should be done is to check to see if the value pass matches a path. If it does, check to see if that file exists. If it doesn't exist, enter the block that existed previous to this commit. If it does exist, attempt require, bail and pass null if something goes awry.

[elliottsj]

Hey, thanks for the feedback!

Before I make changes, I'd like to clarify the reporter priority you're suggesting:

1. Treat the reporter value as a file system path, and check whether the file exists. If it's a relative path, then check it relative to CWD.
2. If the above fails, then treat the value as the prefix in ./reporters/${prefix}Reporter. Try to require() it.
3. If the above fails, then treat the value as a module name passed directly to require(name). This is intended to load a reporter from another npm package.
4. If the above fails, then return null.

I can do the refactor as you described, keeping the original requireReporter function and defining a new function (e.g. requireReporterPath) which checks the path first, then calls requireReporter.

IMO, having a small chain of try / catch is a bit simpler than the recursive call with the local param, since it reads from top-to-bottom like the list above. But I don't feel too strongly about this 😜

[shellscape]

@elliottsj I tweaked this just a bit to follow a different pattern that should make it easier to extend the location of reporters in the future without additional nesting.