[This is not a bug in the port per se, apologies if I am not reporting it in the right place.] devel/hs-git-annex is not available from the pkg repositories anymore (both latest and quarterly, at least for amd64), but https://www.freshports.org/devel/hs-git-annex/ does not list any problem with the port. Unfortunately I cannot confirm that the port actually builds, my machine being very limited resource-wise.
git-annex depends on esqueleto package, which doesn't build with current GHC. So, we have to wait for new esqueleto release to make git-annex available.
It looks like esqueleto was removed as a dependency in http://git-annex.branchable.com/news/version_7.20181121/.
It has and building git annex with stack is possible if you use the system GHC (their prepackaged GHC isn't ino64 compatible).
A commit references this bug: Author: arrowd Date: Thu May 9 14:39:35 UTC 2019 New revision: 501101 URL: https://svnweb.freebsd.org/changeset/ports/501101 Log: Introduce USES=cabal and use it to build Haskell applications. PR: 230186 Reviewed by: mat, tcberner Approved by: tcberner (mentor) Differential Revision: https://reviews.freebsd.org/D19730 Changes: head/Mk/Uses/cabal.mk head/Mk/bsd.options.mk head/converters/hs-aeson-pretty/Makefile head/converters/hs-aeson-pretty/distinfo head/converters/hs-aeson-pretty/pkg-descr head/devel/hs-ShellCheck/Makefile head/devel/hs-ShellCheck/distinfo head/devel/hs-alex/Makefile head/devel/hs-alex/distinfo head/devel/hs-bytestring-nums/Makefile head/devel/hs-bytestring-nums/distinfo head/devel/hs-c2hs/Makefile head/devel/hs-c2hs/distinfo head/devel/hs-c2hs/files/ head/devel/hs-cabal-install/Makefile head/devel/hs-cabal-install/distinfo head/devel/hs-cpphs/Makefile head/devel/hs-cpphs/distinfo head/devel/hs-darcs/Makefile head/devel/hs-darcs/distinfo head/devel/hs-darcs/files/patch-darcs.cabal head/devel/hs-ghc-events/Makefile head/devel/hs-ghc-events/distinfo head/devel/hs-git-annex/Makefile head/devel/hs-git-annex/distinfo head/devel/hs-git-annex/files/patch-Build__Configure.hs head/devel/hs-git-annex/files/patch-Build__DesktopFile.hs head/devel/hs-git-annex/files/patch-Command_Multicast.hs head/devel/hs-git-annex/files/patch-Utility_QuickCheck.hs head/devel/hs-git-annex/files/patch-clock-0.7.2_clock.cabal head/devel/hs-git-annex/files/patch-git-annex.cabal head/devel/hs-haddock/Makefile head/devel/hs-haddock/distinfo head/devel/hs-happy/Makefile head/devel/hs-happy/distinfo head/devel/hs-happy/files/ head/devel/hs-happy/files/patch-happy.cabal head/devel/hs-hasktags/Makefile head/devel/hs-hasktags/distinfo head/devel/hs-hlint/Makefile head/devel/hs-hlint/distinfo head/devel/hs-hoogle/Makefile head/devel/hs-hoogle/distinfo head/devel/hs-hspec-discover/Makefile head/devel/hs-hspec-discover/distinfo head/devel/hs-mueval/Makefile head/devel/hs-mueval/distinfo head/devel/hs-shake/Makefile head/devel/hs-shake/distinfo head/devel/hs-threadscope/Makefile head/devel/hs-threadscope/distinfo head/devel/hs-threadscope/files/ head/devel/hs-threadscope/files/patch-gtk2hs-buildtools-0.13.5.0_c2hs_toplevel_C2HSConfig.hs head/devel/hs-threadscope/files/patch-threadscope.cabal head/devel/stack/Makefile head/devel/stack/distinfo head/devel/stack/files/ head/devel/stack/files/patch-ino64-support head/devel/stack/files/patch-uname head/games/Makefile head/games/hedgewars/Makefile head/games/hedgewars-server/ head/games/hedgewars-server/Makefile head/games/hedgewars-server/distinfo head/games/hedgewars-server/pkg-descr head/games/hs-scroll/Makefile head/games/hs-scroll/distinfo head/games/hs-scroll/files/ head/games/hs-scroll/files/patch-lib_UI_NCurses.chs head/lang/ghc/bsd.hackage.mk head/lang/hs-brainfuck/Makefile head/lang/hs-brainfuck/distinfo head/lang/hs-unlambda/Makefile head/lang/hs-unlambda/distinfo head/math/hs-Agda/Makefile head/print/hs-hscolour/Makefile head/print/hs-hscolour/distinfo head/textproc/cgrep/Makefile head/textproc/cgrep/distinfo head/textproc/hs-lhs2tex/Makefile head/textproc/hs-lhs2tex/distinfo head/textproc/hs-pandoc/Makefile head/textproc/hs-pandoc/distinfo head/textproc/hs-pandoc/files/ head/textproc/hs-pandoc-citeproc/Makefile head/textproc/hs-pandoc-citeproc/distinfo head/textproc/hs-yaml/Makefile head/textproc/hs-yaml/distinfo head/textproc/hs-yaml/pkg-descr head/www/hs-DAV/Makefile head/www/hs-DAV/distinfo head/www/hs-hjsmin/Makefile head/www/hs-hjsmin/distinfo head/www/hs-wai-app-static/Makefile head/www/hs-wai-app-static/distinfo head/www/hs-yesod-bin/Makefile head/www/hs-yesod-bin/distinfo head/www/hs-yesod-bin/files/patch-yesod-bin.cabal head/x11/hs-xmobar/Makefile head/x11/hs-xmobar/distinfo head/x11/hs-xmobar/files/extra-patch-hinotify.cabal head/x11/hs-xmobar/pkg-plist
The port has been updated as part of https://reviews.freebsd.org/D19730