Add an easy abstract type interface

Can be used in place of the macro to give a pass CassetteoOverlay
behavior. The abstract type works by reading the appropriate binding
from the type parameter.

Requires JuliaLang/julia#47749

src/CassetteOverlay.jl

@@ -174,10 +174,15 @@ macro overlaypass(args...)
 
     nonoverlaytype = typeof(CassetteOverlay.nonoverlay)
 
+    if method_table !== :nothing
+        mthd_tbl = :($CassetteOverlay.method_table(::Type{$PassName}) = $(esc(method_table)))
+    else
+        mthd_tbl = nothing
+    end
+
     blk = quote
         $decl_pass
-
-        $CassetteOverlay.method_table(::Type{$PassName}) = $(esc(method_table))
+        $mthd_tbl
 
         @inline function (::$PassName)(f::Union{Core.Builtin,Core.IntrinsicFunction}, args...)
             @nospecialize f args
@@ -187,6 +192,10 @@ macro overlaypass(args...)
             @nospecialize args
             return f(args...)
         end
+        @inline function (self::$PassName)(::typeof(Core._apply_iterate), iterate, f, args...)
+            @nospecialize args
+            return Core.Compiler._apply_iterate(iterate, self, (f,), args...)
+        end
 
         @generated function (pass::$PassName)($(esc(:fargs))...)
             src = $overlay_generator(pass, fargs)
@@ -222,4 +231,18 @@ macro overlaypass(args...)
     return Expr(:toplevel, blk.args...)
 end
 
+abstract type AbstractBindingOverlay{M, S} <: OverlayPass; end
+function method_table(::Type{<:AbstractBindingOverlay{M, S}}) where {M, S}
+    @assert isconst(M, S)
+    return getglobal(M, S)::Core.MethodTable
+end
+@overlaypass AbstractBindingOverlay nothing
+
+struct Overlay{M, S} <: AbstractBindingOverlay{M, S}; end
+function Overlay(mt::Core.MethodTable)
+    @assert isconst(mt.module, mt.name)
+    @assert getglobal(mt.module, mt.name) === mt
+    return Overlay{mt.module, mt.name}()
+end
+
 end # module CassetteOverlay

test/abstract.jl

@@ -0,0 +1,23 @@
+module abstract
+
+using CassetteOverlay, Test
+@MethodTable SinTable
+mutable struct CosCounter <: CassetteOverlay.AbstractBindingOverlay{@__MODULE__, :SinTable}
+    ncos::Int
+end
+
+function (c::CosCounter)(::typeof(cos), args...)
+    c.ncos += 1
+    return cos(args...)
+end
+
+@overlay SinTable sin(x::Union{Float32,Float64}) = cos(x);
+
+let pass! = CosCounter(0)
+    pass!(42) do a
+        sin(a) * cos(a)
+    end
+    @test pass!.ncos == 2
+end
+
+end

test/runtests.jl

@@ -4,4 +4,5 @@ using Test
     @testset "simple" include("simple.jl")
     @testset "math" include("math.jl")
     @testset "misc" include("misc.jl")
+    @testset "abstract" include("abstract.jl")
 end