Better error messages for "invariant violated: multiple results when describing installed package"

[akurilin]

When running stack install below with a custom snapshot, I get the error that I pasted below. It'd be great if the error was more explicit about what exactly went wrong, and perhaps suggestions as far as how to move forward:

$ stack install fr                                                                                                                                                                                                          
yesod-persistent-1.4.0.3: configure
yesod-persistent-1.4.0.3: build
kan-extensions-4.2.3: configure
kan-extensions-4.2.3: build
yesod-persistent-1.4.0.3: copy/register
yesod-form-1.4.4.1: configure
yesod-form-1.4.4.1: build
kan-extensions-4.2.3: copy/register
lens-4.12.3: configure
lens-4.12.3: build
pointed-4.2.0.2: configure
pointed-4.2.0.2: build
pointed-4.2.0.2: copy/register
vector-instances-3.3.1: configure
vector-instances-3.3.1: build
vector-instances-3.3.1: copy/register
mono-traversable-0.9.3: configure
mono-traversable-0.9.3: build
yesod-form-1.4.4.1: copy/register
lens-4.12.3: copy/register
mono-traversable-0.9.3: copy/register
Progress: 7/18singleBuild: invariant violated: multiple results when describing installed package

The code that throws this is here: https://github.com/commercialhaskell/stack/blob/master/src/Stack/Build/Execute.hs#L1110

Also, any advice on how to move past this?

[borsboom]

The "invariant violated" part of that messages means Stack hit a condition that it didn't expect should ever happen and doesn't know how to deal with. In other words: this is a crashing bug, not a bad error message. The reason this shouldn't happen is that Stack unregisters local packages before rebuilding them, meaning there should only ever be a single version of any package in the local package database, but you've hit a condition where, for some reason, there is more than one.

Would you mind sending me the output of stack exec ghc-pkg dump?

First thing I'd try to get past it is rename your .stack-work out of the way, since the problem is likely due to a strange condition within that directory.

[akurilin]

@borsboom - happen to have an email I can forward that to? Probably has some internal info in there I shouldn't be sharing.

[borsboom]

Sure, you can send it to manny@fpcomplete.com.

[meteficha]

Assuming this condition was caused by a misuse of the custom snapshot feature, perhaps the error message could be expanded to include something like: "If you're using custom snapshots, you may have violated one of stack's invariants and may need to wipe your ~/.stack/snapshots cache directory."

[borsboom]

So it looks like there are two versions of yesod-form in your snapshot database: yesod-form-1.4.5 and yesod-form-1.4.4.1 (probably the one just registered). It is possible that you modified your custom snapshot and changed the version number?

[akurilin]

That's very possible, maybe that's the source of the issue. Up to you folks whether you want to surface the specific error to the user more explicitly.

[hesselink]

We also ran into this, and we're also using custom snapshots. I found that I changed the version of a package in the snapshot without renaming the snapshot. So perhaps a message to that effect would be a good idea.

As for fixing it, for us just re-running the original stack command that caused it fixed the problem.

[mgsloan]

This should be resolved in this experimental branch https://github.com/commercialhaskell/stack/tree/863-extensible-snapshots , as a side effect of the work on #863

[Blaisorblade]

Replaced old label in-progress with "in progress" (see #1491 (comment)).

[snoyberg]

I'd be very interested to hear if the #3249 PR for extensible snapshots addresses this, the fact that we cache the snapshot information by a unique hash of the contents of the file would hopefully fix it.

[chris-martin]

I just ran into this using Stack 1.4.0, for what it's worth.

[mpilgrem]

I am closing this issue given the passage of time and because the form of the bug report is different in Stack 2.13.1.