Build is broken when compiling with haddoc or hoogle

[a-stacey]

When building with haddock or hoogle the build hangs:

# haddock
haskell-src-exts-1.20.2: configure
haskell-src-exts-1.20.2: build
Progress 0/5
...


# hoogle
haskell-src-exts-1.20.2: configure
haskell-src-exts-1.20.2: build
Progress 0/4
...

Eventually it times out.

Command:
stack build --fast --file-watch --pedantic --haddock --ghc-options=-Wno-deprecations --exec "stack hoogle" --test --ta -j1

As far as I'm aware this issue is present for both @mas17k and myself which means that its not isolated to a particular platform (both Linux and MacOS).

Original Author: sta358

(Moved with github-migration-0.1.0.0 (package github-migration-0.1.0.0 revision df9f38b))

[paulsamways]

This issue relates to haddock issue: haskell/haddock#837

This has been fixed in a newer GHC, however updating to GHC 8.6 causes us to hit another haddock issue, haskell/haddock#979.