A live Elm cache is required in offline mode

[dwayne]

When I add this patch and try to run elm-review in this version of elm2nix I get the following error:

example> I could not fetch all the data I need about these dependencies of your project:
example> - elm/browser 1.0.2
example> - elm/url 1.0.0
example>
example> Connect to the Internet so I can download and cache the data for future uses.
example> I will try to review the project anyway, but you might get unexpected results

I ran nix build .#reviewedExample -L --keep-failed and checked the Elm cache that I created and I noticed that both elm/browser 1.0.2 and elm/url 1.0.0 were missing docs.json.

I found an old Discourse post where this same issue was experienced but their solutions don't explain why the docs.json issue gets resolved so I did some investigation of my own.

When is docs.json created?

It is created during an elm make. See builder/src/Elm/Details.hs, in particular:

• call writeDocs
• writeDocs implementation

What ultimately calls writeDocs?

• load -> generate -> verifyApp -> verifyDependencies -> verifyDep -> build -> writeDocs
• load is used by make, repl, and reactor

A way forward

Here's what I've learned:

1. elm make generates various files in the Elm cache as it does its thing
2. One of them is docs.json
3. If I let elm make run before I run elm-review then the various files are populated in the Elm cache as required by elm-review
4. In addition, I need the lock file to include all dependencies from both elm.json and review/elm.json

When I follow 3 & 4, it works. See this commit.

What's a live Elm cache?

I'm calling a live Elm cache an Elm cache in which elm make was run at least once on it. All the reachable dependencies would have artifacts.dat, docs.json, and whatever other files that the compiler generates at build time.

What to do with this issue?

I found a solution to my original problem and will be moving forward with my work around but I'm not sure what you'd want to do with this information, if anything. Please feel free to close this issue if there's nothing that can be done by this project.

Out of curiosity, why is docs.json required?

[jfmengels]

Thank you for the detailed issue!

Yes, docs.json is available if you've run elm make on the project at least once. Otherwise, elm-review tries to download them itself (but that's not preferred).

I don't know why those files are not present. I'd love to resolve it nicely.
Are you using prepare-offline or preparing the dependencies somehow yourself? Also, are you reviewing a package or an application?
Could you perhaps figure out which versions of those 2 dependencies you have around in the scenario you gave? (could be no others, but I suspect there may be different ones that the CLI is not looking for somehow)

Out of curiosity, why is docs.json required?

docs.json contains a lot of information about the project: all the available modules, with their contents (functions, types, and their contents) and documentation. We for instance use this to know from which package a reference to SomeModule or SomeModule.someFunction comes from, potentially even looking at its type (we currently don't do that much, but we might later). Without this information, for a lot of things we're running blind. In practice, this mostly makes some dependencies look unused, but there could be other false results (false positives or negatives).

[dwayne]

I don't know why those files are not present. I'd love to resolve it nicely.
Are you using prepare-offline or preparing the dependencies somehow yourself?

They aren't present because I created the Elm cache from scratch and ran elm-review before running elm make.

• https://github.com/dwayne/elm2nix/blob/eb5c4ce05ca67a5c059728d3ac2684b7e29977c3/nix/prepare-elm-home-script.nix
• The preBuildPhases occur before the buildPhase

Also, are you reviewing a package or an application?

An application. This example in particular.

Could you perhaps figure out which versions of those 2 dependencies you have around in the scenario you gave? (could be no others, but I suspect there may be different ones that the CLI is not looking for somehow)

• The elm.json
• The review/elm.json

The versions that are put in the Elm cache are correct. They are elm/browser 1.0.2 and elm/url 1.0.0.