nix ghc/haskell repo compilation failure

gistfile1.txt

echo 'export LD_LIBRARY_PATH="/build/ghc-8.4.4/libraries/process/dist-install/build:/build/ghc-8.4.4/libraries/directory/dist-install/build:/build/ghc-8.4.4/libraries/unix/dist-install/build:/build/ghc-8.4.4/libraries/filepath/dist-install/build:/build/ghc-8.4.4/libraries/time/dist-install/build:/build/ghc-8.4.4/libraries/bytestring/dist-install/build:/build/ghc-8.4.4/libraries/deepseq/dist-install/build:/build/ghc-8.4.4/libraries/array/dist-install/build:/build/ghc-8.4.4/libraries/base/dist-install/build:/build/ghc-8.4.4/libraries/integer-gmp/dist-install/build:/nix/store/38j1yww2crj0zpsn4lnkjcpgd4rjlsyv-gmp-6.1.2/lib:/build/ghc-8.4.4/libraries/ghc-prim/dist-install/build:/build/ghc-8.4.4/rts/dist/build${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"' >> inplace/bin/runghc
cat utils/runghc/runghc.wrapper                                     >> inplace/bin/runghc
chmod +x                                                     inplace/bin/runghc
/nix/store/gahx1w92ldx16a3nacdhi4z050ikzii1-python3.7-sphinx-1.8.3/bin/sphinx-build -b html -d docs/users_guide/.doctrees-html -D latex_paper_size=letter docs/users_guide docs/users_guide/build-html/users_guide
Running Sphinx v1.8.3

Extension error:
The 'ghc-flag' directive is already registered to domain std
make[1]: *** [docs/users_guide/ghc.mk:16: docs/users_guide/build-html/users_guide/index.html] Error 2
make: *** [Makefile:127: all] Error 2
builder for '/nix/store/hc37mvicvrpaxibnwis4b9ah218wazqb-ghc-8.4.4.drv' failed with exit code 2
cannot build derivation '/nix/store/7xcgfysmw4dsv3ijzagqjw7nrihmj23f-my-app-0.1.0.0.drv': 1 dependencies couldn't be built
error: build of '/nix/store/7xcgfysmw4dsv3ijzagqjw7nrihmj23f-my-app-0.1.0.0.drv' failed