use an extension instead of Requires on 1.9 (#549)

Author: KristofferC

Project.toml

@@ -16,6 +16,12 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 WoodburyMatrices = "efce3f68-66dc-5838-9240-27a6d6f5f9b6"
 
+[weakdeps]
+Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
+
+[extensions]
+InterpolationsUnitfulExt = "Unitful"
+
 [compat]
 Adapt = "2, 3"
 AxisAlgorithms = "0.3, 1"
@@ -24,6 +30,7 @@ OffsetArrays = "0.10, 0.11, 1.0.1"
 Ratios = "0.3, 0.4"
 Requires = "1.1"
 StaticArrays = "0.12, 1"
+Unitful = "1"
 WoodburyMatrices = "0.4, 0.5"
 julia = "1.3"
 

ext/InterpolationsUnitfulExt.jl

@@ -0,0 +1,11 @@
+module InterpolationsUnitfulExt
+
+if !isdefined(Base, :get_extension)
+    import ..Unitful, ..Interpolations
+else
+    import Unitful, Interpolations
+end
+
+Interpolations.tweight(A::AbstractArray{T}) where T <: Unitful.Quantity = Interpolations.tweight(Unitful.ustrip(A))
+
+end

src/Interpolations.jl

@@ -38,7 +38,7 @@ export
 
 using LinearAlgebra, SparseArrays
 using StaticArrays, WoodburyMatrices, Ratios, AxisAlgorithms, OffsetArrays
-using ChainRulesCore, Requires
+using ChainRulesCore
 
 using Base: @propagate_inbounds, HasEltype, EltypeUnknown, HasLength, IsInfinite,
     SizeUnknown, Indices
@@ -450,8 +450,14 @@ if VERSION >= v"1.6"
     include("gpu_support.jl")
 end
 
+if !isdefined(Base, :get_extension)
+using Requires
+end
+
+@static if !isdefined(Base, :get_extension)
 function __init__()
-    @require Unitful="1986cc42-f94f-5a68-af5c-568840ba703d" include("requires/unitful.jl")
+    @require Unitful="1986cc42-f94f-5a68-af5c-568840ba703d" include("../ext/InterpolationsUnitfulExt.jl")
+end
 end
 
 end # module