Move FileIO support into extension

Project.toml

@@ -15,9 +15,13 @@ UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 MPIPreferences = "3da0fdf6-3ccc-4f1b-acd9-58baa6c99267"
 
 [weakdeps]
+FileIO = "5789e2e9-d7fb-5bc7-8068-2c6fae9b9549"
 MPI = "da04e1cc-30fd-572f-bb4f-1f8673147195"
+OrderedCollections = "bac558e1-5e72-5ebc-8fee-abe8a469f55d"
 
 [extensions]
+FileIOExt = "FileIO"
+OrderedCollectionsFileIOExt = ["FileIO", "OrderedCollections"]
 MPIExt = "MPI"
 
 [compat]

src/fileio.jl → ext/FileIOExt.jl

@@ -1,4 +1,12 @@
-import .FileIO
+module FileIOExt
+
+import HDF5: File, Group, h5open, fileio_save, fileio_load, _infer_track_order
+@static if isdefined(Base, :get_extension)
+    import FileIO
+else
+    import ..FileIO
+    import Requires: @require
+end
 
 function loadtodict!(d::AbstractDict, g::Union{File,Group}, prefix::String="")
     for k in keys(g)
@@ -14,10 +22,10 @@ end
 _infer_track_order(track_order::Union{Nothing,Bool}, dict::AbstractDict) =
     something(track_order, false)
 
-@require OrderedCollections = "bac558e1-5e72-5ebc-8fee-abe8a469f55d" begin
-    _infer_track_order(
-        track_order::Union{Nothing,Bool}, dict::OrderedCollections.OrderedDict
-    ) = something(track_order, true)
+@static if !isdefined(Base, :get_extension)
+    @require OrderedCollections = "bac558e1-5e72-5ebc-8fee-abe8a469f55d" include(
+        "OrderedCollectionsFileIOExt.jl"
+    )
 end
 
 # load with just a filename returns a flat dictionary containing all the variables
@@ -75,3 +83,5 @@ function fileio_save(
         end
     end
 end
+
+end

ext/OrderedCollectionsFileIOExt.jl

@@ -0,0 +1,16 @@
+module OrderedCollectionsFileIOExt
+
+import HDF5: _infer_track_order
+@static if isdefined(Base, :get_extension)
+    import OrderedCollections
+else
+    import ..OrderedCollections
+end
+
+function _infer_track_order(
+    track_order::Union{Nothing,Bool}, dict::OrderedCollections.OrderedDict
+)
+    return something(track_order, true)
+end
+
+end

src/HDF5.jl

@@ -107,6 +107,11 @@ Returns `true` if the HDF5 libraries were compiled with ros3 support
 """
 has_ros3() = HAS_ROS3[]
 
+# Functions implemented by extensions
+function _infer_track_order end
+function fileio_save end
+function fileio_load end
+
 function __init__()
     # HDF5.API.__init__() is run first
     #
@@ -118,7 +123,11 @@ function __init__()
     ASCII_ATTRIBUTE_PROPERTIES.char_encoding = :ascii
     UTF8_ATTRIBUTE_PROPERTIES.char_encoding = :utf8
 
-    @require FileIO = "5789e2e9-d7fb-5bc7-8068-2c6fae9b9549" include("fileio.jl")
+    @static if !isdefined(Base, :get_extension)
+        @require FileIO = "5789e2e9-d7fb-5bc7-8068-2c6fae9b9549" include(
+            "../ext/FileIOExt.jl"
+        )
+    end
 
     @require H5Zblosc = "c8ec2601-a99c-407f-b158-e79c03c2f5f7" begin
         set_blosc!(p::Properties, val::Bool) =