Add package extension to support InlineStrings in Arrow.jl (#66)

* Add package extension to support InlineStrings in Arrow.jl

Fixes apache/arrow-julia#196.

This utilizes the new package extension feature of Julia 1.9 to
add a conditional dependency on the ArrowTypes.jl package. With
ArrowTypes.jl, it adds the necessary overloads to allow round-
tripping of inline strings through the arrow format. Other language
implementations will read them as normal strings, but in the Julia
implementation, the additional type metadata signal that these strings
were originally inline strings and can be deserialized as such.

I'm explicitly not using the Requires.jl hack for backwards compat w/
older Julia versions because I like the idea of this being sort of a
"beta" feature for users already using 1.9 to see if there are any
unexpected issues that pop up for inline strings in the arrow format.

* Only test package extension on 1.9

Project.toml

@@ -7,6 +7,7 @@ version = "1.4.0"
 Parsers = "69de0a69-1ddd-5017-9359-2bf0b02dc9f0"
 
 [extras]
+Arrow = "69666777-d1a9-59fb-9406-91d4454c9d45"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Serialization = "9e88b42a-f829-5b0c-bbe9-9e923198166b"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
@@ -15,5 +16,11 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 Parsers = "2"
 julia = "1.6"
 
+[weakdeps]
+ArrowTypes = "31f734f8-188a-4ce0-8406-c8a06bd891cd"
+
+[extensions]
+ArrowTypesExt = "ArrowTypes"
+
 [targets]
-test = ["Test", "Random", "Serialization"]
+test = ["Arrow", "Test", "Random", "Serialization"]

ext/ArrowTypesExt.jl

@@ -0,0 +1,15 @@
+module ArrowTypesExt
+
+using ArrowTypes, InlineStrings
+
+for sz in (1, 4, 8, 16, 32, 64, 128, 256)
+    nm = Symbol(:InlineString, max(1, sz - 1))
+    arrow_nm = Symbol("JuliaLang.InlineStrings.", nm)
+    @eval begin
+        ArrowTypes.arrowname(::Type{$nm}) = $(Meta.quot(arrow_nm))
+        ArrowTypes.JuliaType(::Val{$(Meta.quot(arrow_nm))}) = $nm
+        ArrowTypes.fromarrow(::Type{$nm}, ptr::Ptr{UInt8}, len::Int) = $nm(ptr, len)
+    end
+end
+
+end

ext/tests.jl

@@ -0,0 +1,8 @@
+using Test, Arrow, InlineStrings
+
+@testset "basic Arrow.jl interop" begin
+    t = (x = inlinestrings(["a", "b", "sailor"]),)
+    t2 = Arrow.Table(Arrow.tobuffer(t))
+    @test isequal(t.x, t2.x)
+    @test t2.x[1] isa InlineString
+end

test/runtests.jl

@@ -562,3 +562,8 @@ end
     @test repr(String31["foo", "bar"]) == "String31[\"foo\", \"bar\"]"
     @test repr(InlineString[inline1"a", inline15"a"]) == "InlineString[String1(\"a\"), String15(\"a\")]"
 end
+
+# only test package extension on >= 1.9.0
+if VERSION >= v"1.9.0"
+include(joinpath(dirname(pathof(InlineStrings)), "../ext/tests.jl"))
+end