added macro example

example/cool_example.jl

@@ -1,14 +1,47 @@
-cd(@__DIR__)
+#=
+You should be able run this script from any directory with any project settings.
+=#
+
 using Pkg
-# run Pkg.instantiate() the first time you run this code
-Pkg.activate("")
+
+cd(@__DIR__)
+
+# activates the project in the script's directory
+Pkg.activate(".")
+
+# adds the local PackageExtensionsExample package to the script project (don't use Pkg.add here)
+Pkg.develop(path="../")
+
+###################################################################################################
 using PackageExtensionsExample
+
 # cool function should have no methods until Distributions is loaded 
 @assert length(methods(cool_function)) == 0
 
+try
+   cool_function()
+catch e
+   @assert e isa MethodError
+end
+
+# calling @cool_macro here throws a LoadError at the module level
+# @cool_macro
+
+@assert !isdefined(PackageExtensionsExample,:MyExtType)
+
+
+###################################################################################################
 using Distributions 
 # cool function should have 1 method now that Distributions is loaded 
 @assert length(methods(cool_function)) == 1
 
 cool_function()
-# should print "calling cool_function()"
+# should print "calling cool_function()"
+
+@cool_macro
+# should print "calling cool_macro()"
+
+@assert isdefined(PackageExtensionsExample,:MyExtType)
+
+println(PackageExtensionsExample.MyExtType())
+# should show message containing "hello from DistributionsExt"

ext/DistributionsExt.jl

@@ -2,8 +2,13 @@ module DistributionsExt
 
     using PackageExtensionsExample
     using StatsBase
-    import PackageExtensionsExample: cool_function
+    import PackageExtensionsExample: cool_function, @cool_macro
     import Distributions: logpdf
+    export MyExtType
+
+    @kwdef struct MyExtType 
+        msg = "hello from DistributionsExt"
+    end
 
 
     function logpdf(d::MyType)
@@ -15,4 +20,21 @@ module DistributionsExt
         println("calling cool_function()")
     end
 
+    macro cool_macro()
+        :(println("calling cool_macro()"))
+    end
+
+    # this installs exported symbols such as MyExtType to the parent module. Using println instead of @info can save 300ms on compilation.
+    function __init__()
+        # The @spawn is a hack to work around the new mechanisms in Julia 1.11 (in 1.10 you don't need it). This is probably not 100% safe, not knowing if the module loading code being touched is thread safe. It shows what's happening until a better solution is found.
+        Threads.@spawn begin
+            sleep(0.001)
+            Core.eval(PackageExtensionsExample, 
+            quote
+                println("Exporting symbols from DistributionsExt to PackageExtensionsExample")
+                ext = Base.get_extension(PackageExtensionsExample, :DistributionsExt)
+                using .ext
+            end)
+        end
+    end
 end

src/PackageExtensionsExample.jl

@@ -2,8 +2,11 @@ module PackageExtensionsExample
 
     export MyType 
     export cool_function
+    export @cool_macro
 
     struct MyType end
 
     function cool_function end
+
+    macro cool_macro end
 end