Added extension for MCMCChains (#514)

* added extension for MCMCChains

* bump patch versoin

* added entry to .gitignore

* Apply suggestions from code review

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* forgot to add MCMCChains to extras

* Update ext/DynamicPPLMCMCChainsExt.jl

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: torfjelde

Diff for: .gitignore

@@ -3,3 +3,4 @@
 *.jl.mem
 .DS_Store
 Manifest.toml
+**.~undo-tree~

Diff for: Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.23.11"
+version = "0.23.12"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"
@@ -20,6 +20,15 @@ Setfield = "efcf1570-3423-57d1-acb7-fd33fddbac46"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 ZygoteRules = "700de1a5-db45-46bc-99cf-38207098b444"
 
+[weakdeps]
+MCMCChains = "c7f686f2-ff18-58e9-bc7b-31028e88f75d"
+
+[extensions]
+DynamicPPLMCMCChainsExt = ["MCMCChains"]
+
+[extras]
+MCMCChains = "c7f686f2-ff18-58e9-bc7b-31028e88f75d"
+
 [compat]
 AbstractMCMC = "2, 3.0, 4"
 AbstractPPL = "0.6"
@@ -31,6 +40,7 @@ Distributions = "0.23.8, 0.24, 0.25"
 DocStringExtensions = "0.8, 0.9"
 LogDensityProblems = "2"
 MacroTools = "0.5.6"
+MCMCChains = "6"
 OrderedCollections = "1"
 Setfield = "0.7.1, 0.8, 1"
 ZygoteRules = "0.2"

Diff for: ext/DynamicPPLMCMCChainsExt.jl

@@ -0,0 +1,16 @@
+module DynamicPPLMCMCChainsExt
+
+using DynamicPPL: DynamicPPL
+using MCMCChains: MCMCChains
+
+function DynamicPPL.generated_quantities(model::DynamicPPL.Model, chain::MCMCChains.Chains)
+    chain_parameters = MCMCChains.get_sections(chain, :parameters)
+    varinfo = DynamicPPL.VarInfo(model)
+    iters = Iterators.product(1:size(chain, 1), 1:size(chain, 3))
+    return map(iters) do (sample_idx, chain_idx)
+        DynamicPPL.setval_and_resample!(varinfo, chain_parameters, sample_idx, chain_idx)
+        model(varinfo)
+    end
+end
+
+end

Diff for: test/ext/DynamicPPLMCMCChainsExt.jl

@@ -0,0 +1,9 @@
+@testset "DynamicPPLMCMCChainsExt" begin
+    @model demo() = x ~ Normal()
+    model = demo()
+
+    chain = MCMCChains.Chains(randn(1000, 2, 1), [:x, :y], Dict(:internals => [:y]))
+    chain_generated = @test_nowarn generated_quantities(model, chain)
+    @test size(chain_generated) == (1000, 1)
+    @test mean(chain_generated) ≈ 0 atol = 0.1
+end

Diff for: test/runtests.jl

@@ -59,6 +59,10 @@ include("test_util.jl")
             include(joinpath("compat", "ad.jl"))
         end
 
+        @testset "extensions" begin
+            include("ext/DynamicPPLMCMCChainsExt.jl")
+        end
+
         @testset "doctests" begin
             DocMeta.setdocmeta!(
                 DynamicPPL,