If an error occurs while initializing or configuring a package, this
will not stop your Emacs from loading. Instead, use-package
captures the error and reports it in a special *Warnings* popup
buffer, so that you can debug the situation in an otherwise functional
Emacs.
If you are having trouble when starting Emacs, you can pass Emacs the ‘--debug-init’ command line flag. See Initial Options in GNU Emacs Manual. To get even more information when using that flag, add the following to your init file (these options are documented below):
(when init-file-debug
(setq use-package-verbose t
use-package-expand-minimally nil
use-package-compute-statistics t
debug-on-error t))
Since use-package is a macro, the first step when you need to
dig deeper is usually to see what Emacs Lisp code your declaration
expands to. You can either use the command M-x pp-macroexpand-last-sexp, or wrap the use-package declaration in
macroexpand and evaluate it. It is a good idea to include
their output in any bugs you file for use-package.