Forcing globally installed elm-format

[krksgbr]

Hi!
In our project, elm-format is installed as a nix package. This means that in nix-shell we need to be able to run the instance of elm-format provided by nix instead of the one installed by prettier-plugin-elm as a dependency. We'd like to have a way of configuring this behavior. Not sure what the best way would be for passing in configuration, maybe through an environment variable: PRETTIER_PLUGIN_ELM_PREFER_LOCAL=false? Currently we solve this problem through a fork, but it would be nice to have this supported in the official package. Would you accept a PR for this?

[kachkaev]

Hi @krksgbr! I see what you're after.

How about an env variable called PRETTIER_PLUGIN_ELM_CUSTOM_PATH_TO_ELM_FORMAT? When it's set to something, we do this:

prettier-plugin-elm/src/util.ts

Lines 19 to 26 in bbf66dc

	export const formatTextWithElmFormat = (text: string): string => {
	return execa.sync("elm-format", ["--stdin", "--elm-version=0.19"], {
	input: text,
	preferLocal: true,
	localDir: __dirname,
	stripEof: false,
	}).stdout;
	};

↓

export const formatTextWithElmFormat = (text: string): string => {
  const customPathToElmFormat = process.env.PRETTIER_PLUGIN_ELM_CUSTOM_PATH_TO_ELM_FORMAT;
  return execa.sync(customPathToElmFormat || "elm-format", ["--stdin", "--elm-version=0.19"], {
    input: text,
    preferLocal: !!customPathToElmFormat,
    localDir: __dirname,
    stripEof: false,
  }).stdout;
};

What you'll then be able to do is:

export PRETTIER_PLUGIN_ELM_CUSTOM_PATH_TO_ELM_FORMAT=elm-format
prettier --write "**/*.elm"

export PRETTIER_PLUGIN_ELM_CUSTOM_PATH_TO_ELM_FORMAT=/path/to/non-global/elm-format
prettier --write "**/*.elm"

I'm happy to consider a PR that introduces this. It'd be great if you could add test coverage to the change. Upgrading dependencies could be also worth it given the opportunity.

---

UPD: Looks like cache must be made aware of the value too.

[krksgbr]

Awesome:)
Will try and send you a PR today.

[kachkaev]

Cool. I won't be able to release at least for another week and a half, so no rush 😉

[krksgbr]

Hey @kachkaev!

In the meantime, I've had a discussion about this with @knuton. After a bit more careful consideration we came to the conclusion that the implementation proposed above would not be as useful for us as I initially thought.

Two issues we have with it are:

• It would lead to surprising behavior if one doesn't know about having to set the environment variable.
• We're transitioning to the use of Lorri (nix-shell replacement for project development), and in the short-term, it will become a bit of a hassle to set environment variables involving nix paths because some functionality is still missing in Lorri.

What do you think of giving preference to the global installation of elm-format and falling back to the one installed by the plugin when it is not found? I feel like it would be closer to the behavior specified in the elm-format plugin development guidelines.

Specifically:

If the path to elm-format has not [been] explicitly specified by the user, the plugin should automatically find elm-format if it is located on the $PATH or in /usr/local/bin/

[kachkaev]

I see. Let’s then close this issue and reopen it if you have further thoughts.