Use values_as_in_model to extract the parameters from a Transition

Project.toml

@@ -1,6 +1,6 @@
 name = "Turing"
 uuid = "fce5fe82-541a-59a6-adf8-730c64b5f9a0"
-version = "0.31.3"
+version = "0.31.4"
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/mcmc/Inference.jl

@@ -317,11 +317,15 @@ Return a named tuple of parameters.
 """
 getparams(model, t) = t.θ
 function getparams(model::DynamicPPL.Model, vi::DynamicPPL.VarInfo)
-    # Want the end-user to receive parameters in constrained space, so we `link`.
-    vi = DynamicPPL.invlink(vi, model)
-
-    # Extract parameter values in a simple form from the `VarInfo`.
-    vals = DynamicPPL.values_as(vi, OrderedDict)
+    # NOTE: In the past, `invlink(vi, model)` + `values_as(vi, OrderedDict)` was used.
+    # Unfortunately, using `invlink` can cause issues in scenarios where the constraints 
+    # of the parameters change depending on the realizations. Hence we have to use
+    # `values_as_in_model`, which re-runs the model and extracts the parameters
+    # as they are seen in the model, i.e. in the constrained space. Moreover,
+    # this means that the code below will work both of linked and invlinked `vi`.
+    # Ref: https://github.com/TuringLang/Turing.jl/issues/2195
+    # NOTE: We need to `deepcopy` here to avoid modifying the original `vi`.
+    vals = DynamicPPL.values_as_in_model(model, deepcopy(vi))
 
     # Obtain an iterator over the flattened parameter names and values.
     iters = map(DynamicPPL.varname_and_value_leaves, keys(vals), values(vals))

test/Project.toml

@@ -10,6 +10,7 @@ DynamicHMC = "bbc10e6e-7c05-544b-b16e-64fede858acb"
 DynamicPPL = "366bfd00-2699-11ea-058f-f148b4cae6d8"
 FiniteDifferences = "26cc04aa-876d-5657-8c51-4c34ba976000"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
+HypothesisTests = "09f84164-cd44-5f33-b23f-e6b0d136a0d5"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 LogDensityProblems = "6fdf6af0-433a-55f7-b3ed-c6c6e0b8df7c"
 LogDensityProblemsAD = "996a588d-648d-4e1f-a8f0-a84b347e47b1"
@@ -43,6 +44,7 @@ DynamicHMC = "2.1.6, 3.0"
 DynamicPPL = "0.25.1"
 FiniteDifferences = "0.10.8, 0.11, 0.12"
 ForwardDiff = "0.10.12 - 0.10.32, 0.10"
+HypothesisTests = "0.11"
 LogDensityProblems = "2"
 LogDensityProblemsAD = "1.4"
 MCMCChains = "5, 6"

test/mcmc/hmc.jl

@@ -261,4 +261,46 @@
             @test mean(Array(chain)) ≈ 0.2
         end
     end
+
+    @turing_testset "issue: #2195" begin
+        @model function buggy_model()
+            lb ~ Uniform(0, 1)
+            ub ~ Uniform(1.5, 2)
+
+            # HACK: Necessary to avoid NUTS failing during adaptation.
+            try
+                x ~ transformed(Normal(0, 1), inverse(Bijectors.Logit(lb, ub)))
+            catch e
+                if e isa DomainError
+                    Turing.@addlogprob! -Inf
+                    return nothing
+                else
+                    rethrow()
+                end
+            end
+        end
+
+        model = buggy_model();
+        num_samples = 1_000;
+
+        chain = sample(
+            model,
+            NUTS(),
+            num_samples;
+            initial_params=[0.5, 1.75, 1.0]
+        )
+        chain_prior = sample(model, Prior(), num_samples)
+
+        # Extract the `x` like this because running `generated_quantities` was how
+        # the issue was discovered, hence we also want to make sure that it works.
+        results = generated_quantities(model, chain)
+        results_prior = generated_quantities(model, chain_prior)
+
+        # Make sure none of the samples in the chains resulted in errors.
+        @test all(!isnothing, results)
+
+        # The discrepancies in the chains are in the tails, so we can't just compare the mean, etc.
+        # KS will compare the empirical CDFs, which seems like a reasonable thing to do here.
+        @test pvalue(ApproximateTwoSampleKSTest(vec(results), vec(results_prior))) > 0.01
+    end
 end

test/runtests.jl

@@ -17,6 +17,7 @@ using ReverseDiff
 using SpecialFunctions
 using StatsBase
 using StatsFuns
+using HypothesisTests
 using Tracker
 using Turing
 using Turing.Inference