Thanks!

Ohh thanks a lot! Since this issue also exists on release-20.03 I backported your patch as a438aed.

This PR didn't fix Zsh completion, which still complains with:

$ tig -- WARNING: this script is deprecated, please see git-completion.zsh
/nix/store/g92x5762p69g82fwx722gfqf15n4x0rr-tig-2.5.1/share/bash-completion/completions/tig:99: command not found: __git_complete

When using Zsh, git-completion.bash needs to be sourced by tig-completion.zsh with GIT_SOURCING_ZSH_COMPLETION=y.

A better patch would be not to source Git completion from tig-completion.bash when the shell is Zsh

+ # fixes tig-completion __git-complete dependency
+ sed -i '1s;^;[[ -z $ZSH_VERSION ]] && source ${git}/share/bash-completion/completions/git\n;' contrib/tig-completion.bash
+

And substitute git-completion.bash also in tig-completion.zsh (which this PR missed), so it can be source properly from tig-completion.zsh instead of using the patched source command at the top of tig-completion.bash.

     substituteInPlace contrib/tig-completion.zsh \
-      --replace 'e=$(dirname ''${funcsourcetrace[1]%:*})/tig-completion.bash' "e=$out/etc/bash_completion.d/tig-completion.bash"
+      --replace 'e=$(dirname ''${funcsourcetrace[1]%:*})/tig-completion.bash' "e=$out/share/bash-completion/completions/tig" \
+      --replace 'e=$(dirname ''${funcsourcetrace[1]%:*})/git-completion.bash' 'e=${git}/share/bash-completion/completions/git'

Not sure if the syntax is right (I just edited the files manually), but the point is clear I think. Both tig-completion.bash and git-completion.bash should be replaced in tig-completion.zsh.

I have no idea how to setup Nix to create and test the patch, that's why I am commenting here.