nixos/shells: avoid overriding the environment for child shells

A shared exported guard `__NIXOS_SET_ENVIRONMENT_DONE` is introduced that can
be used to prevent child shells from sourcing `system.build.setEnvironment`
the second time.

This fixes e.g. `nix run derivation` when run from e.g. ZSH through the console or
ssh. Before this Bash would resource the common environment resetting the `PATH`
environment variable.

We also export `system.build.setEnvironment` to `/etc/set-environment` making it
easy to reset the common environment with `. /etc/set-environment` when
needed and to grep for environment variables in `/etc` (which was the
motivation of #30418).

This reverts changes made in b00a3fc6fd82834114771f2115a2b032f0ebfe29
(the original #30418).

1 files changed, 3 insertions, 1 deletions

diff --git a/nixos/modules/programs/bash/bash.nix b/nixos/modules/programs/bash/bash.nix
index 69a1a482d07..e5f5c8d0943 100644
--- a/nixos/modules/programs/bash/bash.nix
+++ b/nixos/modules/programs/bash/bash.nix
@@ -126,7 +126,9 @@ in
     programs.bash = {
 
       shellInit = ''
-        ${config.system.build.setEnvironment.text}
+        if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+            . ${config.system.build.setEnvironment}
+        fi
 
         ${cfge.shellInit}
       '';