ucc: CUDA fixups

pkgs/by-name/uc/ucc/package.nix

@@ -1,4 +1,4 @@
-{
+inputs@{
   autoconf,
   automake,
   config,
@@ -15,6 +15,7 @@
   enableSse42 ? stdenv.hostPlatform.sse4_2Support,
 }:
 let
+  inherit (lib.attrsets) getLib;
   inherit (lib.lists) optionals;
   inherit (lib.strings) concatStringsSep;
 
@@ -22,15 +23,21 @@ let
     cuda_cccl
     cuda_cudart
     cuda_nvcc
+    cuda_nvml_dev
     cudaFlags
+    nccl
     ;
+
+  stdenv = throw "Use effectiveStdenv instead";
+  effectiveStdenv = if enableCuda then cudaPackages.backendStdenv else inputs.stdenv;
 in
-stdenv.mkDerivation (finalAttrs: {
+effectiveStdenv.mkDerivation (finalAttrs: {
   __structuredAttrs = true;
-  # TODO: When strictDeps is enabled, the CUDA build fails during configurePhase because it can't find all the CUDA
-  # dependencies. As such, we hold off on enabling strictDeps until CUDA compilation works.
-  # https://github.com/openucx/ucc/blob/0c0fc21559835044ab107199e334f7157d6a0d3d/config/m4/cuda.m4
-  strictDeps = false;
+  # TODO(@connorbaker):
+  # When strictDeps is enabled, `cuda_nvcc` is required as the argument to `--with-cuda` in `configureFlags` or else
+  # configurePhase fails with `checking for cuda_runtime.h... no`.
+  # This is odd, especially given `cuda_runtime.h` is provided by `cuda_cudart.dev`, which is already in `buildInputs`.
+  strictDeps = true;
 
   pname = "ucc";
   version = "1.3.0";
@@ -55,7 +62,7 @@ stdenv.mkDerivation (finalAttrs: {
       substituteInPlace "$comp" \
         --replace-quiet \
           "/bin/bash" \
-          "${stdenv.shell}"
+          "${effectiveStdenv.shell}"
     done
   '';
 
@@ -70,8 +77,20 @@ stdenv.mkDerivation (finalAttrs: {
     ++ optionals enableCuda [
       cuda_cccl
       cuda_cudart
+      cuda_nvml_dev
+      nccl
     ];
 
+  # NOTE: With `__structuredAttrs` enabled, `LDFLAGS` must be set under `env` so it is assured to be a string;
+  # otherwise, we might have forgotten to convert it to a string and Nix would make LDFLAGS a shell variable
+  # referring to an array!
+  env.LDFLAGS = builtins.toString (
+    optionals enableCuda [
+      # Fake libnvidia-ml.so (the real one is deployed impurely)
+      "-L${getLib cuda_nvml_dev}/lib/stubs"
+    ]
+  );
+
   preConfigure = ''
     ./autogen.sh
   '';
@@ -81,7 +100,7 @@ stdenv.mkDerivation (finalAttrs: {
     ++ optionals enableSse42 [ "--with-sse42" ]
     ++ optionals enableAvx [ "--with-avx" ]
     ++ optionals enableCuda [
-      "--with-cuda=${cuda_cudart}"
+      "--with-cuda=${cuda_nvcc}"
       "--with-nvcc-gencode=${concatStringsSep " " cudaFlags.gencode}"
     ];