dub-to-nix: fetch submodules for git dependencies (#548514)

pkgs/build-support/dlang/builddubpackage/import-dub-lock.nix

@@ -41,6 +41,7 @@ let
       src = fetchgit {
         url = repository;
         rev = version;
+        fetchSubmodules = true; # this is the default, but let's be explicit
         inherit sha256;
       };
     };

pkgs/build-support/dlang/dub-to-nix/dub-to-nix.py

@@ -57,7 +57,7 @@ for pname in depsDict:
         repository = depDict["repository"]
         strippedRepo = repository[4:]
         eprint(f"Fetching {pname}@{version} ({strippedRepo})")
-        command = ["nix-prefetch-git", strippedRepo, version]
+        command = ["nix-prefetch-git", "--fetch-submodules", strippedRepo, version]
         rawRes = subprocess.run(command, check=True, text=True, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL).stdout
         sha256 = json.loads(rawRes)["sha256"]
         lockedDepsDict[pname] = {"version": version, "repository": strippedRepo, "sha256": sha256}