singularity-tools: deprecate build helpers mkLayer and shellScript

Deprecate singularity-tools.mkLayer and singularity-tools.shellScript,
for they are no longer related to image building.

Use writers.writeBash instead of singularity-tools.shellScript.

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -126,6 +126,8 @@
 
 - `singularity-tools` have the `storeDir` argument removed from its override interface and use `builtins.storeDir` instead.
 
+- Two build helpers in `singularity-tools`, i.e., `mkLayer` and `shellScript`, are deprecated, as they are no longer involved in image-building. Maintainers will remove them in future releases.
+
 - The `budgie` and `budgiePlugins` scope have been removed and their packages
   moved into the top level scope (i.e., `budgie.budgie-desktop` is now
   `budgie-desktop`)

pkgs/build-support/singularity-tools/default.nix

@@ -5,8 +5,10 @@
   runCommand,
   vmTools,
   writeClosure,
+  writers,
   writeScript,
   # Native build inputs
+  buildPackages,
   e2fsprogs,
   util-linux,
   # Build inputs
@@ -19,27 +21,37 @@ let
   defaultSingularity = singularity;
 in
 rec {
+  # TODO(@ShamrockLee): Remove after Nixpkgs 24.11 branch-off.
   shellScript =
-    name: text:
-    writeScript name ''
-      #!${runtimeShell}
-      set -e
-      ${text}
-    '';
+    lib.warn
+      "`singularity-tools.shellScript` is deprecated. Use `writeScript`, `writeShellScripts` or `writers.writeBash` instead."
+      (
+        name: text:
+        writeScript name ''
+          #!${runtimeShell}
+          set -e
+          ${text}
+        ''
+      );
 
+  # TODO(@ShamrockLee): Remove after Nixpkgs 24.11 branch-off.
   mkLayer =
-    {
-      name,
-      contents ? [ ],
-      # May be "apptainer" instead of "singularity"
-      projectName ? (singularity.projectName or "singularity"),
-    }:
-    runCommand "${projectName}-layer-${name}" { inherit contents; } ''
-      mkdir $out
-      for f in $contents ; do
-        cp -ra $f $out/
-      done
-    '';
+    lib.warn
+      "`singularity-tools.mkLayer` is deprecated, as it is no longer used to implement `singularity-tools.buildImages`."
+      (
+        {
+          name,
+          contents ? [ ],
+          # May be "apptainer" instead of "singularity"
+          projectName ? (singularity.projectName or "singularity"),
+        }:
+        runCommand "${projectName}-layer-${name}" { inherit contents; } ''
+          mkdir $out
+          for f in $contents ; do
+            cp -ra $f $out/
+          done
+        ''
+      );
 
   buildImage =
     {
@@ -53,8 +65,14 @@ rec {
     }:
     let
       projectName = singularity.projectName or "singularity";
-      runAsRootFile = shellScript "run-as-root.sh" runAsRoot;
-      runScriptFile = shellScript "run-script.sh" runScript;
+      runAsRootFile = buildPackages.writers.writeBash "run-as-root.sh" ''
+        set -e
+        ${runAsRoot}
+      '';
+      runScriptFile = writers.writeBash "run-script.sh" ''
+        set -e
+        ${runScript}
+      '';
       result = vmTools.runInLinuxVM (
         runCommand "${projectName}-image-${name}.sif"
           {