follow https://pkgdocs.julialang.org/dev/creating-packages/#Conditional-loading-of-code-in-packages-(Extensions)

Author: vpuri3

Project.toml

@@ -19,6 +19,12 @@ StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
 Tricks = "410a4b4d-49e4-4fbc-ab6d-cb71b17b3775"
 VertexSafeGraphs = "19fa3120-7c27-5ec5-8db8-b0b0aa330d6f"
 
+[weakdeps]
+Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
+
+[extensions]
+SparseDiffToolsZygote = "Zygote"
+
 [compat]
 Adapt = "3.0"
 ArrayInterface = "6, 7"

src/SparseDiffTools.jl

@@ -68,16 +68,16 @@ Base.@pure __parameterless_type(T) = Base.typename(T).wrapper
 parameterless_type(x) = parameterless_type(typeof(x))
 parameterless_type(x::Type) = __parameterless_type(x)
 
-#if !isdefined(Base, :get_extension)
+if !isdefined(Base, :get_extension)
     using Requires
-#end
+end
 
 function __init__()
-    #@static if !isdefined(Base, :get_extension)
+    @static if !isdefined(Base, :get_extension)
         @require Zygote="e88e6eb3-aa80-5325-afca-941959d7151f" begin
             include("../ext/SparseDiffToolsZygote.jl")
         end
-    #end
+    end
 end
 
 end # module