[Backport release-26.05] nixos/nixpkgs: add zstd flavored nixexprs tarballs (#539631)

doc/release-notes/rl-2611.section.md

@@ -4,7 +4,17 @@
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
-- Create the first release note entry in this section!
+- The {file}`nixexprs.tar.xz` tarball will be discontinued together with Nixpkgs
+  27.05 after 2027-12-31. Migrate to the {file}`nixexprs.tar.zst` tarball
+  instead.
+
+  This affects for example users who pull Nixpkgs as a flake input from
+  https://channels.nixos.org:
+
+  ```diff
+  -nixpkgs.url = "https://channels.nixos.org/nixos-26.05/nixexprs.tar.xz";
+  +nixpkgs.url = "https://channels.nixos.org/nixos-26.05/nixexprs.tar.zst";
+  ```
 
 ## Backward Incompatibilities {#sec-nixpkgs-release-26.11-incompatibilities}
 

nixos/doc/manual/release-notes/rl-2611.section.md

@@ -4,7 +4,17 @@
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
-- Create the first release note entry in this section!
+- The {file}`nixexprs.tar.xz` tarball will be discontinued together with Nixpkgs
+  27.05 after 2027-12-31. Migrate to the {file}`nixexprs.tar.zst` tarball
+  instead.
+
+  This affects for example users who pull Nixpkgs as a flake input from
+  https://channels.nixos.org:
+
+  ```diff
+  -nixpkgs.url = "https://channels.nixos.org/nixos-26.05/nixexprs.tar.xz";
+  +nixpkgs.url = "https://channels.nixos.org/nixos-26.05/nixexprs.tar.zst";
+  ```
 
 ## New Modules {#sec-release-26.11-new-modules}
 

nixos/lib/make-channel.nix

@@ -18,7 +18,10 @@ pkgs.releaseTools.makeSourceTarball {
   officialRelease = false; # FIXME: fix this in makeSourceTarball
   inherit version versionSuffix;
 
-  buildInputs = [ pkgs.nix ];
+  buildInputs = with pkgs; [
+    nix
+    zstd
+  ];
 
   distPhase = ''
     rm -rf .git
@@ -32,6 +35,35 @@ pkgs.releaseTools.makeSourceTarball {
     NIX_STATE_DIR=$TMPDIR nix-env -f ../$releaseName/default.nix -qaP --meta --show-trace --xml \* > /dev/null
     cd ..
     chmod -R u+w $releaseName
-    tar cfJ $out/tarballs/$releaseName.tar.xz $releaseName
+
+    # The compression tasks are shortlived; use all available CPUs (-T0) to
+    # prioritize fast channel advancement.
+    XZ_OPT="-T0" tar \
+      --create \
+      --file=$out/tarballs/$releaseName.tar.xz \
+      --xz \
+      --absolute-names \
+      --owner=0 \
+      --group=0 \
+      --numeric-owner \
+      --format=gnu \
+      --sort=name \
+      --mtime="@$SOURCE_DATE_EPOCH" \
+      --hard-dereference \
+      $releaseName
+
+    tar \
+      --create \
+      --file="$out/tarballs/$releaseName.tar.zst" \
+      --use-compress-program="zstd -19 -T0" \
+      --absolute-names \
+      --owner=0 \
+      --group=0 \
+      --numeric-owner \
+      --format=gnu \
+      --sort=name \
+      --mtime="@$SOURCE_DATE_EPOCH" \
+      --hard-dereference \
+      $releaseName
   '';
 }

pkgs/top-level/make-tarball.nix

@@ -24,6 +24,7 @@ pkgs.releaseTools.sourceTarball {
     jq
     lib-tests
     brotli
+    zstd
   ];
 
   configurePhase = ''
@@ -63,6 +64,9 @@ pkgs.releaseTools.sourceTarball {
   #   Some context: https://github.com/NixOS/infra/issues/438
   distPhase = ''
     mkdir -p $out/tarballs
+
+    # The compression tasks are shortlived; use all available CPUs (-T0) to
+    # prioritize fast channel advancement.
     XZ_OPT="-T0" tar \
       --create \
       --xz \
@@ -79,5 +83,22 @@ pkgs.releaseTools.sourceTarball {
       --mode=ug+w \
       --hard-dereference \
       $src $(pwd)/{.version-suffix,.git-revision}
+
+    tar \
+      --create \
+      --use-compress-program="zstd -19 -T0" \
+      --file=$out/tarballs/$releaseName.tar.zst \
+      --absolute-names \
+      --transform="s|^$src|$releaseName|g" \
+      --transform="s|^$(pwd)|$releaseName|g" \
+      --owner=0 \
+      --group=0 \
+      --numeric-owner \
+      --format=gnu \
+      --sort=name \
+      --mtime="@$SOURCE_DATE_EPOCH" \
+      --mode=ug+w \
+      --hard-dereference \
+      $src $(pwd)/{.version-suffix,.git-revision}
   '';
 }