mpich: deprecate stringly-typed withPm

nixos/doc/manual/release-notes/rl-2405.section.md

@@ -171,5 +171,7 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
   replaces the need for the `extraPackages` option, this option will be
   deprecated in future releases.
 
+- The `mpich` package expression now requires `withPm` to be a list, e.g. `"hydra:gforker"` becomes `[ "hydra" "gforker" ]`.
+
 - QtMultimedia has changed its default backend to `QT_MEDIA_BACKEND=ffmpeg` (previously `gstreamer` on Linux or `darwin` on MacOS).
   The previous native backends remain available but are now minimally maintained. Refer to [upstream documentation](https://doc.qt.io/qt-6/qtmultimedia-index.html#ffmpeg-as-the-default-backend) for further details about each platform.

pkgs/development/libraries/mpich/default.nix

@@ -13,11 +13,7 @@
 } :
 
 let
-  processManagers = if builtins.isList withPm then
-    withPm
-  else
-    builtins.filter builtins.isString (builtins.split ":" withPm);
-  withPm' = if processManagers != [ ] then builtins.concatStringsSep ":" processManagers else "no";
+  withPmStr = if withPm != [ ] then builtins.concatStringsSep ":" withPm else "no";
 in
 
 assert (ch4backend.pname == "ucx" || ch4backend.pname == "libfabric");
@@ -35,7 +31,7 @@ stdenv.mkDerivation  rec {
 
   configureFlags = [
     "--enable-shared"
-    "--with-pm=${withPm'}"
+    "--with-pm=${withPmStr}"
   ] ++ lib.optionals (lib.versionAtLeast gfortran.version "10") [
     "FFLAGS=-fallow-argument-mismatch" # https://github.com/pmodels/mpich/issues/4300
     "FCFLAGS=-fallow-argument-mismatch"
@@ -60,7 +56,7 @@ stdenv.mkDerivation  rec {
 
   meta = with lib; {
     # As far as we know, --with-pmix silently disables all of `--with-pm`
-    broken = pmixSupport && processManagers != [ ];
+    broken = pmixSupport && withPm != [ ];
 
     description = "Implementation of the Message Passing Interface (MPI) standard";