Feature request

What is the expected behavior?

It seems like the new version of WatchPack (v2.0.0) are getting rid of the mtimes variable. However, from my research it seems like that variable was the only way to get the list of changed files that triggered a re-compilation (source).
As such, there should be an alternative way to get this list of changed files.

What is motivation or use case for adding/changing the behavior?

Seems like a pretty useful feature for the watchRun hook, as there are already a couple people (including me) that use it.

How should this be implemented in your opinion?

Watchpack actually provides the info we need, in the variable filesModified that it passes to Watching.js. However, Watching.js doesn't use it at all. Ideally I think this variable should be provided in the watchRun hook, but it should also be fine to just store it as a property just like how it's done with removedFiles, eg in Watching.js:

this.compiler.filesModified = filesModified;

Are you willing to work on this yourself?
yes