deal with vendor=cray but no gtl

lib/MPIPreferences/Project.toml

@@ -1,7 +1,7 @@
 name = "MPIPreferences"
 uuid = "3da0fdf6-3ccc-4f1b-acd9-58baa6c99267"
 authors = []
-version = "0.1.9"
+version = "0.1.10"
 
 [deps]
 Libdl = "8f399da3-3557-5675-b5ff-fb832c97cbdb"

lib/MPIPreferences/src/MPIPreferences.jl

@@ -170,11 +170,14 @@ function use_system_binary(;
     preloads = []
     preloads_env_switch = nothing
     cclibs = []
-    if vendor === nothing
+    if isnothing(vendor)
     elseif vendor == "cray"
         cray_pe = CrayParser.analyze_cray_cc()
         library_names = [cray_pe.libmpi]
-        preloads = [cray_pe.libgtl]
+        # if there is no preload, then set preloads to "nothing" instead of
+        # "[nothing]" -- the later of which would cause an error when trying to
+        # dump as toml
+        preloads = isnothing(cray_pe.libgtl) ? nothing : [cray_pe.libgtl]
         preloads_env_switch = cray_pe.gtl_env_switch
         cclibs = cray_pe.cclibs
     else

lib/MPIPreferences/src/parse_cray_cc.jl

@@ -6,38 +6,59 @@ reduce(f::Function)::Function = Base.Fix1(Base.reduce, f)
 
 struct CrayPE
     libmpi::String
-    libgtl::String
+    libgtl::Union{String, Nothing}
     cclibs::Vector{String}
     gtl_env_switch::String
-
-    CrayPE(mpi_dl::T, gtl_dl::T, cclibs::Vector{T}) where T <:AbstractString = new(
+
+    CrayPE(
+        mpi_dl::T,
+        gtl_dl::T,
+        cclibs::Vector{T}
+    ) where T <:AbstractString = new(
         "lib" * mpi_dl * ".so", # Assuming Linux -- CrayPE is only avaialbe for linux anyway
         "lib" * gtl_dl * ".so",
         cclibs,
         "MPICH_GPU_SUPPORT_ENABLED"
     )
+    CrayPE(
+        mpi_dl::T,
+        gtl_dl::Nothing,
+        cclibs::Vector{T}
+    ) where T <:AbstractString = new(
+        "lib" * mpi_dl * ".so", # Assuming Linux -- CrayPE is only avaialbe for linux anyway
+        nothing,
+        cclibs,
+        "MPICH_GPU_SUPPORT_ENABLED"
+    )
 end
 
 const libmpi_prefix = "mpi_"
 const libgtl_prefix = "mpi_gtl_"
 
+function only_or_nothing(iter)
+    if length(iter) == 0
+        return nothing
+    end
+    only(iter)
+end
+
 function cray_mpi(libs)
     x = libs |>
-        filter(x-> startswith(x, libmpi_prefix)) |> 
+        filter(x-> startswith(x, libmpi_prefix)) |>
         filter(x->!startswith(x, libgtl_prefix))
     return only(x)
 end
 
 function cray_gtl(libs)
     x = libs |>
-        filter(x->startswith(x, libmpi_prefix)) |> 
+        filter(x->startswith(x, libmpi_prefix)) |>
         filter(x->startswith(x, libgtl_prefix))
-    return only(x)
+    return only_or_nothing(x)
 end
 
 function other_libs(libs)
     x = libs |>
-        filter(x->!startswith(x, libmpi_prefix)) |> 
+        filter(x->!startswith(x, libmpi_prefix)) |>
         filter(x->!startswith(x, libgtl_prefix))
     return x
 end