SubArrays cause an illegal naming error

[tyleransom]

If I try to save a SubArray (created from the @views macro) to a MAT file, I get an illegal naming error. Consider the following MWE using MAT.jl v0.10.1:

using Random, MAT

Random.seed!(1234)
a = rand(5)
@show a
@show typeof(a)
@views a = a[[1,3,4,2,5]]
@show a
@show typeof(a)

matwrite("test.mat", Dict("a" => a))

This returns the following:

julia> include("MWE.jl")
a = [0.5908446386657102, 0.7667970365022592, 0.5662374165061859, 0.4600853424625171, 0.7940257103317943]
typeof(a) = Array{Float64,1}
a = [0.5908446386657102, 0.5662374165061859, 0.4600853424625171, 0.7667970365022592, 0.7940257103317943]
typeof(a) = SubArray{Float64,1,Array{Float64,1},Tuple{Array{Int64,1}},false}
ERROR: LoadError: Invalid variable name or key "1": variable names must start with a letter and contain only alphanumeric characters and underscore
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] check_valid_varname at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:290 [inlined]
 [3] check_struct_keys(::Array{String,1}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:507
 [4] m_write(::MAT.MAT_HDF5.MatlabHDF5File, ::HDF5.Group, ::String, ::Tuple{Array{Int64,1}}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:533
 [5] m_write(::MAT.MAT_HDF5.MatlabHDF5File, ::HDF5.File, ::String, ::Array{String,1}, ::Array{Any,1}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:518
 [6] m_write(::MAT.MAT_HDF5.MatlabHDF5File, ::HDF5.File, ::String, ::SubArray{Float64,1,Array{Float64,1},Tuple{Array{Int64,1}},false}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:533
 [7] write(::MAT.MAT_HDF5.MatlabHDF5File, ::String, ::SubArray{Float64,1,Array{Float64,1},Tuple{Array{Int64,1}},false}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT_HDF5.jl:546
 [8] matwrite(::String, ::Dict{String,SubArray{Float64,1,Array{Float64,1},Tuple{Array{Int64,1}},false}}; compress::Bool) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT.jl:157
 [9] matwrite(::String, ::Dict{String,SubArray{Float64,1,Array{Float64,1},Tuple{Array{Int64,1}},false}}) at /hpc/home/tmr17/.julia/packages/MAT/f523T/src/MAT.jl:148
 [10] top-level scope at /hpc/group/econ/tmr17/DropoutRR/Simulations/BackwardSimMay2020/MWE.jl:11
 [11] include(::String) at ./client.jl:439
 [12] top-level scope at REPL[1]:1
in expression starting at /hpc/group/econ/tmr17/DropoutRR/Simulations/BackwardSimMay2020/MWE.jl:11