Opening a specific literate haskell file causes emacs process to hang

[bhrgunatha]

emacs: GNU Emacs 27.2 - Arch linux official package
haskell-mode: haskell-mode-20210429.117 - installed from melpa and updated today.

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Following along Graham Hutton's emacs videos I tried to open up his literate sudoku file and emacs immediately becomes unresponsive and hangs - no screen refresh, no response to keyboard - even mashing ESC or C-g has no effect.

Looking at the active processes emacs is maxed out at 25% on my quad core machine. Seems to be stuck in an infinite loop

I've pared down my config to the simplest case but I still get the same result.

(use-package haskell-mode
  :commands haskell-mode)

It's OK with a minimal literate file :

Some text at the start of the file.

> module Test where
> f v = 2 * v

I haven;t tried to find any other more complex literate files but I DO remember looking at a literate version of the original by Richard Bird some months ago and haskell-mode was handling that as expected.

Sorry I don't have firm dates or version numbers for when it stopped working.

[purcell]

Thanks for reporting this. I can confirm it. It seems to have been caused by 4ea8774ee29e230f04c28423d2abba33ba072f42, which was a fix contributed by @goose121 in #1740 to address issue #1594. I don't know why it causes the issue (though we have a reproducible case), but in the meantime I have reverted that commit.