I've been using LSP for most programming languages for a while now. HLS is
really very good now, but I've found that it doesn't warn on quite all things
I'd like it to so I find myself having to swap between the
'haskell-ghc checkers. However, since flycheck supports chaining checkers I
thought there must be a way to have both checkers active at the same time.
The naive approach didn't work due to load order of things in Spacemacs so I had to experiment a bit to find something that works.
The first issue was to make sure that HLS is available at all. I use
together with direnv extensively and I had noticed that
lsp-mode tried to load
direnv had put it in the
$PATH. I think the
'lsp-beforeinitialize-hook is the hook to use for this:
(add-hook 'lsp-before-initialize-hook #'direnv-update-environment))
I made a several attempt to chain the checkers but kept on getting
errors due to the
'lsp checker not being defined yet. Another problem
I ran into was that the checkers were chained too late, resulting in
having to manually run
flycheck-buffer on the first file I opened.
(Deferred loading is a brilliant thing, but make some things really
difficult to debug.) After quite a bit of experimenting and reading the
description of various hooks I did find something that works:
(with-eval-after-load 'lsp-mode (defun magthe:lsp-next-checker () (flycheck-add-next-checker 'lsp '(warning . haskell-ghc))) (add-hook 'lsp-lsp-haskell-after-open-hook #'magthe:lsp-next-checker))
Of course I have no idea if this is the easiest or most elegant solution but it does work for my testcases:
- Open a file in a project,
SPC p l- choose project - choose a Haskell file.
- Open a project,
SPC p lfollowed by
C-d, and then open a Haskell file.
Suggestions for improvements are more than welcome, of course.