chore: Nix: print cumulative and per-line execution time on CI

.github/workflows/nix-ci.yml

@@ -14,7 +14,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     defaults:
       run:
-        shell: nix --experimental-features "nix-command flakes" shell .#nix -c bash -euo pipefail {0}
+        # Can't use `nix-shell` without configured nixpkgs path on macOS
+        shell: nix -v --experimental-features "nix-command flakes" run .#ciShell -- bash -euxo pipefail {0}
     strategy:
       matrix:
         include:

flake.nix

@@ -58,6 +58,12 @@
         temci = (import temci {}).override { doCheck = false; };
         nix = nix-pinned;
         nixpkgs = nixpkgs.legacyPackages.${system};
+        ciShell = writeShellScriptBin "ciShell" ''
+          set -o pipefail
+          export PATH=${nix-pinned}/bin:${moreutils}/bin:$PATH
+          # prefix lines with cumulative and individual execution time
+          "$@" |& ts -i "(%.S)]" | ts -s "[%M:%S"
+        '';
       };
 
       defaultPackage = packages.lean;