Emacs freezes when opening Haskell files

[jgertm]

Description

When opening a Haskell file via projectile-find-file or helm-find-files, Emacs freezes for about 10 seconds before displaying the new buffer and responding to control inputs.

Reproduction guide 🪲

• Start Emacs
• Navigate to a Stack project
• Highlight source file
• Press enter
• Wait
• Buffer becomes available for editing after approximately 10 seconds

Observed behaviour: 👀 💔

• Emacs freezes before showing the file
• htop shows a stack invocation to take up lots of time. (How do I record the output of (h)top?)

Expected behaviour: ❤️ 😄

• File opens and is available for editing immediately

System Info 💻

• OS: gnu/linux (NixOS)
• Emacs: 25.3.1
• Spacemacs: 0.200.9
• Spacemacs branch: master (rev. 0e06bba)
• Graphic display: t
• Distribution: spacemacs
• Editing style: vim
• Completion: helm
• Layers:

(agda asciidoc
      (auto-completion :variables auto-completion-return-key-behavior 'complete auto-completion-tab-key-behavior 'cycle auto-completion-enable-snippets-in-popup t auto-completion-enable-help-tooltip t auto-completion-enable-sort-by-usage t)
      (clojure :variables cider-font-lock-dynamically
               '(macro core deprecated function)
               cljr-suppress-middleware-warnings t cider-inject-dependencies-at-jack-in t cider-cljs-lein-repl "(do (use 'figwheel-sidecar.repl-api) (start-figwheel!) (cljs-repl))")
      colors
      (csv :variables csv-separators
           '(";" ",")
           csv-field-quotes
           '("\""))
      dash docker emacs-lisp erlang evil-cleverparens evil-commentary
      (evil-snipe :variables evil-snipe-enable-alternate-f-and-t-behaviors t)
      (forth :variables forth-executable "gforth")
      games
      (git :variables magit-push-arguments
           '("--set-upstream")
           magit-diff-section-arguments
           '("--ignore-space-change" "-M" "-C")
           magit-diff-refine-hunk 'all magit-log-arguments
           '("--graph" "--color" "--decorate" "--stat" "-n64")
           magit-rebase-arguments
           '("--autostash"))
      github graphviz
      (haskell :variables haskell-completion-backend 'dante haskell-ask-also-kill-buffers nil haskell-process-suggest-add-package nil haskell-process-suggest-language-pragmas t haskell-process-suggest-remove-import-lines nil haskell-stylish-on-save t)
      helm html ibuffer
      (latex :variables latex-enable-auto-fill t TeX-view-program-selection
             '(((output-dvi has-no-display-manager)
                "dvi2tty")
               ((output-dvi style-pstricks)
                "dvips and gv")
               (output-dvi "xdvi")
               (output-pdf "xdg-open")
               (output-html "xdg-open")))
      major-modes markdown nixos
      pandoc plantuml purescript python rebox restclient
      (rust :variables rust-enable-racer t)
      (shell :variables shell-default-shell 'ansi-term shell-default-term-shell "zsh")
      shell-scripts
      (spell-checking :variables spell-checking-enable-by-default nil enable-flyspell-auto-completion t)
      (sql :variables sql-capitalize-keywords t)
      syntax-checking themes-megapack
      (version-control :variables version-control-diff-tool 'git-gutter+ vc-follow-symlinks t)
      vimscript yaml)

• System configuration features: XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS NOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

[CeleritasCelery]

see if some of the suggestions in #4730 help

[DavidM-D]

I had this issue, a workaround is to run stack build on the project you're trying to open before you try to edit the file.

The haskell plugin was trying to download a new version of GHC in the background, hence the slow file opening.