Make Semantic fast

[tuhdo]

Limit the parsing scope to file, local and project. The choices are listed in semanticdb-find-default-throttle variable.

[syl20bnr]

Thank you ! 👍
Cherry-picked into develop branch, you can safely delete your branch.

[braham-snyder]

This alone didn't quite work for me, due to a mode-local default for emacs-lisp-mode in my /usr/local/Cellar/emacs-plus/25.2/share/emacs/25.2/lisp/cedet/semantic/db-el.el.gz that kept resetting my semanticdb-find-default-throttle to include omniscience:

(defvar-mode-local emacs-lisp-mode semanticdb-find-default-throttle
  '(project omniscience)
  "Search project files, then search this omniscience database.
It is not necessary to do system or recursive searching because of
the omniscience database.")

This resets the mode-local version to the global, for what it's worth:

(use-package semantic
  :config
  (setq-mode-local emacs-lisp-mode
                   semanticdb-find-default-throttle
                   (default-value 'semanticdb-find-default-throttle)))

which might or might not result in some missing semantic functionality, but I was really just looking for stickyfunc-mode, which this appears to suffice for.

Lastly, just for those curious, I found that snippet in db-el.el.gz from the semantic directory (find-variable semanticdb-find-default-throttle to find the directory) then spacemacs/search-ag with input -z semanticdb-find-default-throttle (if you happen to .[git]ignore .gz files, you'll also need -u). Note also that -- as of writing -- rg does not suffice here: it cannot search compressed files.

[quicknir]

Can this be re-opened, and @braham-snyder 's suggested change be merged into spacemacs proper somehow? Right now, it's still the case that by default in a vanilla spacemacs setup with only semantic added, performance in emacs-lisp mode is simply terrible. Surely this isn't ok?