Changing resolver from lts-5.11 to lts-6.1 triggers "Missing build tools" error

[chreekat]

Snowdrift at eabedbd builds fine. If I change to using lts-6.1, however, I get the error that mentions #595 (reproduced below).

$ stack build
No packages found in snapshot which provide a "hsc2hs" executable,
which is a build-tool dependency of "skein". Missing build-tools may be
caused by dependencies of the build-tool being overridden by
extra-deps. This should be fixed soon - see this issue
https://github.com/commercialhaskell/stack/issues/595

No packages found in snapshot which provide a "hsc2hs" executable,
which is a build-tool dependency of "postgresql-libpq" Missing
build-tools may be caused by dependencies of the build-tool being
overridden by extra-deps. This should be fixed soon - see this issue
https://github.com/commercialhaskell/stack/issues/595

While constructing the BuildPlan the following exceptions were
encountered:

--  Failure when adding dependencies:
      hjsmin: needed (>=0.1 && <0.2), 0.2.0.1 found (latest applicable is 0.1.5.3)
    needed for package Snowdrift-0.1.4 with flags:
      dev: True

[sigrlami]

Noticed this in docker when moved from 5.15 to 6.5, local build doesn't bring this error

[chreekat]

Update: the error about hsc2hs is spurious. There's nothing wrong with it. The actual error preventing the build was at the bottom: Snowdrift.cabal needed to relax its restriction on hjsmin.

I think the issue still stands, but it is about spurious errors.

[mgsloan]

I've fixed this - it now checks if the tool is on the PATH before warning.