Use nix --accept-flake-config option rather than yes | in CI tests (#1626)

https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-accept-flake-config

Author: yvan-sraka

.buildkite/pipeline.yml

@@ -41,7 +41,7 @@ steps:
 
   - label: 'Check that the haskell.nix roots do not require IFDs'
     command:
-      - yes | nix build .#roots.x86_64-linux --option allow-import-from-derivation false
+      - nix build .#roots.x86_64-linux --accept-flake-config --option allow-import-from-derivation false
     agents:
       system: x86_64-linux
 

scripts/update-external.nix

@@ -35,5 +35,7 @@ in
 
     cd ..
 
-    yes | nix --experimental-features 'nix-command flakes' flake lock --update-input ${name}
+    nix flack lock --accept-flake-config \
+                   --experimental-features 'nix-command flakes' \
+                   --update-input ${name}
   ''

test/nix.conf

@@ -20,16 +20,7 @@ printf "*** Cleaning package build directories..." >& 2
 rm -rvf */cabal.project.local */.ghc.environment* */dist */dist-newstyle */.stack-work
 echo >& 2
 
-# This was needed is first place to make hix template / flake devShell examples
-# not require interactive user confirmation. Because the IOG nix cache settings
-# are defined in the `nixConfig` flake attribute.
-if [ ! -z ${CI+x} ]; then
-  printf "*** Set custom nix.conf for CI ..." >& 2
-  export XDG_CONFIG_HOME=$HOME/.config
-  mkdir -p $XDG_CONFIG_HOME/nix
-  cp ./nix.conf $XDG_CONFIG_HOME/nix
-  echo >& 2
-fi
+alias nix="nix --accept-flake-config"
 
 printf "*** Running the nix-build tests...\n" >& 2
 nix build $NIX_BUILD_ARGS \