The build is unreachable.
Build log
> /tmp/stackage-build2455$ stack unpack xmlgen-0.6.2.2@sha256:934b45cf548f1356da051c1d87c327f9444d47a66376929faf47fe935b0999e5
Unpacked xmlgen-0.6.2.2 to /tmp/stackage-build2455/xmlgen-0.6.2.2/
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
[1 of 1] Compiling Main ( Setup.hs, Setup.o )
Linking Setup ...
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ./Setup configure --package-db=clear --package-db=global --package-db=/home/circleci/project/builds/nightly/pkgdb --libdir=/home/circleci/project/builds/nightly/lib --bindir=/home/circleci/project/builds/nightly/bin --datadir=/home/circleci/project/builds/nightly/share --libexecdir=/home/circleci/project/builds/nightly/libexec --sysconfdir=/home/circleci/project/builds/nightly/etc --docdir=/home/circleci/project/builds/nightly/doc/xmlgen-0.6.2.2 --htmldir=/home/circleci/project/builds/nightly/doc/xmlgen-0.6.2.2 --haddockdir=/home/circleci/project/builds/nightly/doc/xmlgen-0.6.2.2
Configuring xmlgen-0.6.2.2...
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ./Setup build
Preprocessing library for xmlgen-0.6.2.2..
Building library for xmlgen-0.6.2.2..
[1 of 1] Compiling Text.XML.Generator ( src/Text/XML/Generator.hs, dist/build/Text/XML/Generator.o )
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ./Setup copy
Installing library in /home/circleci/project/builds/nightly/lib/x86_64-linux-ghc-8.7.20181122/xmlgen-0.6.2.2-1gbelqLK10K6Umqfe1y3vD
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2455/xmlgen-0.6.2.2$ ./Setup register
Registering library for xmlgen-0.6.2.2..