The build is unreachable.

Build log

> /tmp/stackage-build2451$ stack unpack pure-zlib-0.6.4@sha256:1ec97bd76f0b56f3183a3fec9e06ba7caaf145584ed6af3ec9d57eb10d474c52
Unpacked pure-zlib-0.6.4 to /tmp/stackage-build2451/pure-zlib-0.6.4/
> /tmp/stackage-build2451/pure-zlib-0.6.4$ 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-build2451/pure-zlib-0.6.4$ ./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/pure-zlib-0.6.4 --htmldir=/home/circleci/project/builds/nightly/doc/pure-zlib-0.6.4 --haddockdir=/home/circleci/project/builds/nightly/doc/pure-zlib-0.6.4
Configuring pure-zlib-0.6.4...
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ./Setup build
Preprocessing library for pure-zlib-0.6.4..
Building library for pure-zlib-0.6.4..
[1 of 6] Compiling Codec.Compression.Zlib.Adler32 ( src/Codec/Compression/Zlib/Adler32.hs, dist/build/Codec/Compression/Zlib/Adler32.o )
[2 of 6] Compiling Codec.Compression.Zlib.HuffmanTree ( src/Codec/Compression/Zlib/HuffmanTree.hs, dist/build/Codec/Compression/Zlib/HuffmanTree.o )
[3 of 6] Compiling Codec.Compression.Zlib.OutputWindow ( src/Codec/Compression/Zlib/OutputWindow.hs, dist/build/Codec/Compression/Zlib/OutputWindow.o )
[4 of 6] Compiling Codec.Compression.Zlib.Monad ( src/Codec/Compression/Zlib/Monad.hs, dist/build/Codec/Compression/Zlib/Monad.o )
[5 of 6] Compiling Codec.Compression.Zlib.Deflate ( src/Codec/Compression/Zlib/Deflate.hs, dist/build/Codec/Compression/Zlib/Deflate.o )

src/Codec/Compression/Zlib/Deflate.hs:107:11: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In a multi-way if alternative:
        Guards do not cover entire pattern space
    |
107 |        if | code <= 15 ->
    |           ^^^^^^^^^^^^^^^...
[6 of 6] Compiling Codec.Compression.Zlib ( src/Codec/Compression/Zlib.hs, dist/build/Codec/Compression/Zlib.o )
Preprocessing executable 'deflate' for pure-zlib-0.6.4..
Building executable 'deflate' for pure-zlib-0.6.4..
[1 of 1] Compiling Main             ( Deflate.hs, dist/build/deflate/deflate-tmp/Main.o )
Linking dist/build/deflate/deflate ...
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ./Setup copy
Installing library in /home/circleci/project/builds/nightly/lib/x86_64-linux-ghc-8.7.20181114/pure-zlib-0.6.4-HVSdgOmEe4h1iGpMdfJMKt
Installing executable deflate in /home/circleci/project/builds/nightly/bin
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ghc -clear-package-db -global-package-db -package-db=/home/circleci/project/builds/nightly/pkgdb Setup
> /tmp/stackage-build2451/pure-zlib-0.6.4$ ./Setup register
Registering library for pure-zlib-0.6.4..