Report all missing packages together

[hdgarrood]

If there are a number of packages which are listed as dependencies in my spago.dhall but which do not exist in my package set, spago reports these one by one. For example:

$ spago build
spago: Package `fixed-precision` does not exist in package set
# Add `fixed-precision` ...
$ spago build
spago: Package `reflection` does not exist in package set
# Add `reflection` ...
$ spago build
...

I think it would be better to report all missing packages together, if possible. Of course it won't always be possible to do so: suppose package A depends on package B, and package B depends on C, and I add A as an addition without adding B or C; in this case we might not know that C is missing until we add B.

For a minimal reproduction example, run spago init in an empty directory, and modify the spago.dhall file as follows:

{-
Welcome to a Spago project!
You can edit this file as you like.
-}
{ name =
    "my-project"
, dependencies =
    [ "effect", "console", "psci-support", "blah", "what" ]
, packages =
    ./packages.dhall
}

and then run spago build. The error you receive is:

spago: Package `blah` does not exist in package set

However, it would be nicer to get something like

spago: The following packages do not exist in your package set:
  - blah
  - what

[f-f]

Nice report, thanks 🙂

Agreed that this is not good behaviour and reporting all errors at the same time is much better. The fix should be quite fine: on line 101 instead of calling die we should accumulate the missing packages in the fold and then die at the end if any:
https://github.com/spacchetti/spago/blob/05815ce7a7f2cbf0767a421e2ebf6b028385e69d/app/Spago/Packages.hs#L88-L104