A heads up to Doom users: doom upgrade will break itself when updating Doom past b9933e6. The only way to avoid this is to update manually (with git pull && doom sync -u), but most users will likely have already run doom upgrade before they read this, so:
You will first see this error:
Click to reveal error message
> Preparing to upgrade Doom Emacs and its packages...
- A new version of Doom Emacs is available!
Old revision: a9866e37e4 (3 hours ago)
New revision: 615848e3a7 (52 minutes ago)
Link to diff: https://github.com/doomemacs/doomemacs/compare/a9866e37e45b43785116ef474c8cd6aa9b5185dd...615848e3a71ca9ecd4e50cd7abc49eedc2fbea23
View the comparison diff in your browser? (y or n) n
Proceed with upgrade? (y or n) y
> Upgrading Doom Emacs...
> Cleaning .elc files
- No elc files to clean
x There was an unexpected runtime error
Message: File is missing
Details: ("Opening input file" "No such file or directory" "/home/hlissner/emacs.d/core/packages.el")
(progn (insert-file-contents (doom-path doom-core-dir "packages.el")) (if (re-search-forward "(package! straight" nil t) (pr...
(unwind-protect (progn (insert-file-contents (doom-path doom-core-dir "packages.el")) (if (re-search-forward "(package! stra...
(save-current-buffer (set-buffer temp-buffer) (unwind-protect (progn (insert-file-contents (doom-path doom-core-dir "package...
(let ((temp-buffer (generate-new-buffer " *temp*" t))) (save-current-buffer (set-buffer temp-buffer) (unwind-protect (progn ...
(equal straight-recipe (doom-upgrade--get-straight-recipe))
(if (equal straight-recipe (doom-upgrade--get-straight-recipe)) nil (doom-print (doom-print--format (doom-print--class 'item...
(let ((straight-recipe (doom-upgrade--get-straight-recipe))) (or (and (= 0 (car (doom-call-process "git" "reset" "--hard" ta...
(let ((doom-print-indent (+ (if t doom-print-indent-increment 0) doom-print-indent))) (doom-compile-clean) (let ((straight-r...
(if (not (or auto-accept-p (y-or-n-p "Proceed with upgrade?"))) (ignore (doom-print (doom-print--format (doom-print--class '...
(cond ((and (null this-rev) (null new-rev)) (error "Failed to get revisions for %s" target-remote)) ((equal this-rev new-rev...
! Wrote extended backtrace to ~/emacs.d/.local/logs/cli.doom.220731015104.962288.error
And from that point on doom upgrade will no longer work; always throwing up Failed to fetch from upstream errors and failing to upgrade. A git pull alone may not be enough to recover from this.
To spare you the pain of nuking your Doom install and reinstalling everything, an easy workaround is to first reset to a safe commit (like a9866e3) before upgrading manually:
Another heads up: the next few weeks will be a little unstable while the rewritten CLI trickles in. In particular, there is one more breaking change coming up sometime in August that will require a reinstall of all your packages (thanks to a rewritten package manager) and an update to your doom! block (thanks to Doom’s modules being moved out to its own repo, plus a new syntax for pulling in remote module libraries from your doom! block).
I’ll post an announcement like this one when it happens.
Yes, once done and stable, doom upgrade will be that upgrade path. The manual method exists only for emergencies (and may change, but will always be documented in the output of doom help upgrade). 
If, by then, you’ve updated beyond b9933e6 then it may work. But if you haven’t, then no. The manual update is required.
The problem right now is that I’m adding all of doom upgrade's safety and automatic migration mechanics between now and the v3.0 release, but that doesn’t help folks upgrading to v3.0 (and the changes aren’t backwards compatible), so a manual update will likely be necessary once more. I’ll go into more detail once in the announcement for that release though.
There will be one more method after the v3 release, where you can pin Doom in your doom! block, and doom sync will up/downgrade itself as desired, but I’ll share more on that another time. ↩︎
Is this still an issue? I haven’t upgraded my Doom Emacs since July since I’m afraid that it might break if I do. The OP says the a new announcement would be released within a few weeks, but it seems to have been a few months, and no new announcements have been made regarding this problem.