diagrams library not present in lts-11.0

[kostmo]

What is the best way to find out what resulted in dropping the diagrams library from the new LTS series?

E.g. is there a specific command we can run locally to observe a build breakage (and therefore possibly contribute a fix)?

[DanBurton]

In LTS 11, we upgraded to lens-4.16, but diagrams-lib requires lens < 4.16.

It can take some getting used to in order to figure out that this was the reason, but the simplest method I can recommend is:

stack unpack diagrams
cd diagrams-1.4
echo 'resolver: lts-11.0' > stack.yaml
stack build

Note the missing dependencies, and repeat the process for each of those in turn to see why they were excluded.

Eventually you get

In the dependencies for diagrams-lib-1.4.2:
    diagrams-solve must match >=0.1 && <0.2, but the stack configuration has
                   no specified version (latest matching version is 0.1.1)
    dual-tree must match >=0.2 && <0.3, but the stack configuration has no
              specified version (latest matching version is 0.2.1)
    lens-4.16 from stack configuration does not match >=4.6 && <4.16 (latest
              matching version is 4.15.4)

[DanBurton]

A good way to find out why something has been removed is usually to grep it in Stackage's build-constraints.yaml file. In most cases there will be a comment pointing you in the right direction. However there were many removals in order to get LTS 11 out the door so I'm not confident that they were all well commented.

[DanBurton]

Once diagrams is ready for inclusion in LTS 11, please open an issue on https://github.com/fpco/lts-haskell/issues. Thanks!