From 071e28c869d3b0c5b3c1105da42f2a8e3ac4c1e2 Mon Sep 17 00:00:00 2001
From: Ronny Pfannschmidt <opensource@ronnypfannschmidt.de>
Date: Thu, 8 Sep 2022 13:08:57 +0200
Subject: [PATCH] home-environment: fix activation on new style profiles

When using the new style profiles we get conflicts when trying to
replace the old `home-path` derivation. To avoid this conflict we
delete the old `home-path` before the install.

Unfortunately, `nix profile` does not yet have a equivalent for
`nix-env --set` and we have to do this hackish workaround. See

  https://github.com/NixOS/nix/issues/6349

for the associated issue in Nix.

Fixes #2848

(cherry picked from commit ccc9164b76e4167873ed819f0fb014635453ec68)
---
 modules/home-environment.nix | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/modules/home-environment.nix b/modules/home-environment.nix
index 9c0a7a1cf..c52d8d9c7 100644
--- a/modules/home-environment.nix
+++ b/modules/home-environment.nix
@@ -592,22 +592,37 @@ in
         ''
       else
         ''
+          function nixReplaceProfile() {
+            local oldNix="$(which nix)"
+
+            nix profile list \
+              | { grep 'home-manager-path$' || test $? = 1; } \
+              | awk -F ' ' '{ print $4 }' \
+              | cut -d ' ' -f 4 \
+              | xargs -t $DRY_RUN_CMD nix profile remove $VERBOSE_ARG
+
+            $DRY_RUN_CMD $oldNix profile install $1
+          }
+
           if [[ -e "$nixProfilePath"/manifest.json ]] ; then
             INSTALL_CMD="nix profile install"
+            INSTALL_CMD_ACTUAL="nixReplaceProfile"
             LIST_CMD="nix profile list"
             REMOVE_CMD_SYNTAX='nix profile remove {number | store path}'
           else
             INSTALL_CMD="nix-env -i"
+            INSTALL_CMD_ACTUAL="$DRY_RUN_CMD nix-env -i"
             LIST_CMD="nix-env -q"
             REMOVE_CMD_SYNTAX='nix-env -e {package name}'
           fi
 
-          if ! $DRY_RUN_CMD $INSTALL_CMD ${cfg.path} ; then
+          if ! $INSTALL_CMD_ACTUAL ${cfg.path} ; then
             echo
             _iError $'Oops, Nix failed to install your new Home Manager profile!\n\nPerhaps there is a conflict with a package that was installed using\n"%s"? Try running\n\n    %s\n\nand if there is a conflicting package you can remove it with\n\n    %s\n\nThen try activating your Home Manager configuration again.' "$INSTALL_CMD" "$LIST_CMD" "$REMOVE_CMD_SYNTAX"
             exit 1
           fi
-          unset INSTALL_CMD LIST_CMD REMOVE_CMD_SYNTAX
+          unset -f nixReplaceProfile
+          unset INSTALL_CMD INSTALL_CMD_ACTUAL LIST_CMD REMOVE_CMD_SYNTAX
         ''
     );