Johnny Depp & Amber Heard's Witness List a Who's Who of Hollywood

Johnny Depp and Amber Heard are going back to court to settle who defamed who once and for all -- and their witness list includes a ton of A-listers ... who'll have to take the stand.

With the trial set to kick off next month in Virginia, just about all the legal docs are filed for witnesses and exhibits ... and reports say the likes of James Franco, Elon Musk and Paul Bettany, among others, are going to be dragged into court and be forced to testify.

Franco and Musk are on Amber's witness list -- this after Johnny alleged she'd had affairs with each of them during their marriage -- and they'll presumably speak on that. Both guys are said to be beaming in via video link ... so they won't be there in person.

"Animal Kingdom" actress Ellen Barkin is also on Heard's witness list, as are reps for huge orgs like Disney, Warner Bros, WME the ACLU and even the LAPD ... which will mostly offer records that she finds pertinent to help make her case.

For his part, Depp has Marvel actor Paul Bettany testifying on his behalf -- Bettany was also roped into the U.K. libel case that JD lost ... having old text messages they once exchanged read aloud in court. Ya gotta imagine they'll get into that again here.

There's more to be unearthed, including correspondence between Heard and her "Aquaman" costar Jason Momoa, director James Wan, director Zack Snyder and CAA chief Bryan Lourd. There are also emails between Depp and J.K. Rowling and Jack White that'll be addressed.

In case you need a refresher ... both exes are suing each other for defamation, and it seems the judge is going to hear each of their claims in one fell swoop, which is probably why there are so many witnesses/submitted evidence -- they're trying to bury this at long last.

This specific claim of defamation got started after Johnny sued Amber for $50 million following a WaPo op-ed piece in which she characterized herself as a victim of domestic violence ... without ever saying his name. Still, he felt that was enough to take her to court over.

Amber countersued for $100 mil, and despite each of them filing to have the other person's case tossed ... both cases have been given the green light to proceed.

Remember, this all follows a major blow JD suffered across the pond ... where he lost a libel case after a newspaper labeled him a "wifebeater," which a judge ruled was mostly true.

In spite of that, he's forging ahead in similar territory here in the States ... all in an attempt to clear his name and get his career back on track. As you know, he's claimed that Hollywood has blacklisted him in the wake of the U.K. ruling ... all while maintaining his innocence.