Add error hint for MethodErrors on LogDensityModel (#146)

Project.toml

@@ -1,9 +1,9 @@
 name = "AbstractMCMC"
 uuid = "80f14c24-f653-4e6a-9b94-39d6b0f70001"
-keywords = ["markov chain monte carlo", "probablistic programming"]
+keywords = ["markov chain monte carlo", "probabilistic programming"]
 license = "MIT"
 desc = "A lightweight interface for common MCMC methods."
-version = "5.2.0"
+version = "5.3.0"
 
 [deps]
 BangBang = "198e06fe-97b7-11e9-32a5-e1d131e6ad66"

src/AbstractMCMC.jl

@@ -88,4 +88,18 @@ include("stepper.jl")
 include("transducer.jl")
 include("logdensityproblems.jl")
 
+if isdefined(Base.Experimental, :register_error_hint)
+    function __init__()
+        Base.Experimental.register_error_hint(MethodError) do io, exc, argtypes, _
+            if Base.parentmodule(exc.f) == LogDensityProblems &&
+                any(a -> a <: LogDensityModel, argtypes)
+                print(
+                    io,
+                    "\n`AbstractMCMC.LogDensityModel` is a wrapper and does not itself implement the LogDensityProblems.jl interface. To use LogDensityProblems.jl methods, access the inner type with (e.g.) `logdensity(model.logdensity, params)` instead of `logdensity(model, params)`.",
+                )
+            end
+        end
+    end
+end
+
 end # module AbstractMCMC

test/logdensityproblems.jl

@@ -22,6 +22,15 @@
         @test model.logdensity === ℓ
 
         @test_throws ArgumentError AbstractMCMC.LogDensityModel(mylogdensity)
+
+        try
+            LogDensityProblems.logdensity(model, ones(10))
+        catch exc
+            @test exc isa MethodError
+            if isdefined(Base.Experimental, :register_error_hint)
+                @test occursin("is a wrapper", sprint(showerror, exc))
+            end
+        end
     end
 
     @testset "fallback for log densities" begin