Syntax `^:` causes Emacs to freeze.

[ZachFontenot]

This happened to me about a half a year ago on Arch Linux with obviously older Emacs and older clojure-mode. Both using Prelude. I wasn't able to reproduce merely with clojure-mode, so steps include downloading prelude.

Expected behavior

Adding ^: to def and defn don't freeze emacs

Actual behavior

^: freezes emacs

Steps to reproduce the problem

Download Prelude Emacs. Open either a clj or cljs file. Type (def ^:something) or (defn ^:something) or even just (def ^:)/(defn ^:). I've reliably been able to reproduce if it doesn't happen initially by typing (defn ^:something) and then M-backspace to delete back to the colon. Will include a screen shot of cpu profiler.

I know a screenshot is not necessarily the best, but I'm having trouble logging it otherwise.

Environment & Version information

clojure-mode version

clojure-mode (version 5.13.0)

Emacs version

GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin19.6.0, NS appkit-1894.60 Version 10.15.7 (Build 19H114))
of 2021-04-24

Operating system

MacOSX 10.15.7 Catalina

[ZachFontenot]

Also, it seems that after this happens and I quit via ctrl-g Emacs still consumes high cpu

[vemv]

It might be interesting to try reproducing this on CI.

For example one could have unit tests for these inputs. Having the build green would be a pretty good signal. Then if possible one could check if CPU was increased in said CI environment

If the issue can't be reproduced, perhaps flycheck or company-mode (per your screenshot) are making an assumption that isn't true. Maybe a race condtion? Given there's a timer involved.

[vemv]

Released as clojure-mode 5.15.0, which will be available within a couple hours