From 9deef256a2301a6a741bafbaa02b4201afe9d0c8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aleix=20Bon=C3=A9?= <aleix.boneribo@bsc.es>
Date: Tue, 28 Oct 2025 16:27:26 +0100
Subject: [PATCH] Add quickShell to build devshells quickly

---
 overlay.nix                  |  1 +
 pkgs/quick-shell/default.nix | 76 ++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+)
 create mode 100644 pkgs/quick-shell/default.nix

diff --git a/overlay.nix b/overlay.nix
index 3b02ae30..f9484128 100644
--- a/overlay.nix
+++ b/overlay.nix
@@ -19,6 +19,7 @@ let
     cudainfo = prev.callPackage ./pkgs/cudainfo/default.nix { };
     #extrae = callPackage ./pkgs/extrae/default.nix { }; # Broken and outdated
     gpi-2 = callPackage ./pkgs/gpi-2/default.nix { };
+    quickShell = import ./pkgs/quick-shell/default.nix { pkgs = final; };
     intelPackages_2023 = callPackage ./pkgs/intel-oneapi/2023.nix { };
     jemallocNanos6 = callPackage ./pkgs/nanos6/jemalloc.nix { };
     # FIXME: Extend this to all linuxPackages variants. Open problem, see:
diff --git a/pkgs/quick-shell/default.nix b/pkgs/quick-shell/default.nix
new file mode 100644
index 00000000..e0a1c907
--- /dev/null
+++ b/pkgs/quick-shell/default.nix
@@ -0,0 +1,76 @@
+{ pkgs }:
+
+# This builds devshells using passthru to populate packages and inputsFrom
+# lazily.
+#
+# Packages prefixed with @ are added to inputsFrom and the rest are
+# added to packages. This makes it possible to obtain a devshell with combining
+# inputsFrom and packages from the comand line:
+#
+# $ nix develop .#quickShell.@nosv.clang-tools.ovni.@tampi
+#
+# is equivalent to:
+#
+#   with pkgs; mkShell {
+#     packages = [ clang-tools ovni ];
+#     inputsFrom = [ nosv tampi ];
+#   }
+#
+
+let
+  inherit (builtins) attrNames getAttr listToAttrs;
+  inherit (pkgs) lib;
+
+  # list of all packages' names
+  names = attrNames pkgs;
+
+  # generate a attributes containing the selected packages + all the available
+  # packages in names ("" -> packages and "@" -> inputsFrom)
+  go =
+    selected:
+    let
+      mkAttrs =
+        isInputs:
+        (map (
+          name:
+          let
+            pkg = getAttr name pkgs;
+          in
+          {
+            name = (if isInputs then "@" else "") + name;
+            value = go (
+              if isInputs then
+                {
+                  inherit (selected) packages;
+                  inputsFrom = selected.inputsFrom ++ [ pkg ];
+                }
+              else
+                {
+                  inherit (selected) inputsFrom;
+                  packages = selected.packages ++ [ pkg ];
+                }
+            );
+          }
+        ) names);
+
+      attrs = listToAttrs ((mkAttrs true) ++ (mkAttrs false));
+
+      drv = pkgs.mkShell {
+        inherit (selected) inputsFrom packages;
+        name = # build a label from inputsFrom
+          if (selected.inputsFrom == [ ]) then
+            "nix-quick-shell"
+          else
+            lib.concatStringsSep "-" (map (v: v.pname or v.name or "unknown") selected.inputsFrom);
+      };
+    in
+    drv.overrideAttrs {
+      passthru = attrs // {
+        _passthru = drv.passthru;
+      };
+    };
+in
+go {
+  inputsFrom = [ ];
+  packages = [ ];
+}