Warn when concretising a dynamic index on a GrowableArray & when creating a GrowableArray

src/model.jl

@@ -283,10 +283,11 @@ instead:
 
 ```jldoctest condition
 julia> vnt = @vnt begin
+           @template m = zeros(2)
            m[2] := 1.0
        end
 VarNamedTuple
-└─ m => PartialArray size=(2,) data::DynamicPPL.VarNamedTuples.GrowableArray{Float64, 1}
+└─ m => PartialArray size=(2,) data::Vector{Float64}
         └─ (2,) => 1.0
 
 julia> m = condition(model, vnt)(); (m[1] != 1.0 && m[2] == 1.0)

src/varnamedtuple/getset.jl

@@ -358,6 +358,7 @@ function make_leaf_singleindex(value, coptic::AbstractPPL.Index, template)
         # have to make a GrowableArray. No need to use `kw` since make_leaf already errors
         # if there are uninterpretable keyword indices.
         template_sz = get_maximum_size_from_indices(coptic.ix...)
+        _warn_growable_array_creation(template_sz)
         GrowableArray(Array{pa_eltype}(undef, template_sz))
     end
     pa_mask = similar(pa_data, Bool)
@@ -408,6 +409,7 @@ function make_leaf_multiindex(value, coptic::AbstractPPL.Index, template)
     else
         # No template, or incorrectly typed template
         template_sz = get_maximum_size_from_indices(coptic.ix...)
+        _warn_growable_array_creation(template_sz)
         GrowableArray(Array{pa_eltype}(undef, template_sz))
     end
     pa_mask = similar(pa_data, Bool)

src/varnamedtuple/macro.jl

@@ -78,6 +78,14 @@ julia> @vnt begin
             x[1] := 1.0
             y[1, 1] := 2.0
        end
+┌ Warning: Creating a growable `Base.Array` of dimension 1 to store values. This may not match the actual type or size of the actual `AbstractArray` that will be used inside the DynamicPPL model.
+│
+│  If this is not the type or size that you expect, please see: https://turinglang.org/docs/uri/growablearray
+└ @ DynamicPPL.VarNamedTuples /path/to/DynamicPPL.jl/src/varnamedtuple/partial_array.jl:823
+┌ Warning: Creating a growable `Base.Array` of dimension 2 to store values. This may not match the actual type or size of the actual `AbstractArray` that will be used inside the DynamicPPL model.
+│
+│  If this is not the type or size that you expect, please see: https://turinglang.org/docs/uri/growablearray
+└ @ DynamicPPL.VarNamedTuples /path/to/DynamicPPL.jl/src/varnamedtuple/partial_array.jl:823
 VarNamedTuple
 ├─ x => PartialArray size=(1,) data::DynamicPPL.VarNamedTuples.GrowableArray{Float64, 1}
 │       └─ (1,) => 1.0

src/varnamedtuple/partial_array.jl

@@ -101,6 +101,13 @@ Base.getindex(ga::GrowableArray, ix::CartesianIndex) = getindex(ga.data, ix)
 # multi-element indexing
 Base.getindex(ga::GrowableArray, ix...) = GrowableArray(getindex(ga.data, ix...))
 Base.setindex!(ga::GrowableArray, value, ix...) = setindex!(ga.data, value, ix...)
+# This function is exported so we can override it!
+function AbstractPPL.concretize_top_level(idx::Index, val::GrowableArray)
+    if any(ix -> ix isa AbstractPPL.DynamicIndex, idx.ix)
+        _warn_growable_array_extraction()
+    end
+    return concretize_top_level(idx, val.data)
+end
 
 function throw_kw_error()
     throw(
@@ -399,7 +406,7 @@ function Base.getindex(pa::PartialArray, inds::Vararg{Any}; kw...)
         # you index with `x[end]` for example, `inds` is already concretised outside of this
         # function.
         if any(ind -> ind isa AbstractPPL.DynamicIndex || ind isa Colon, inds)
-            _warn_growable_array()
+            _warn_growable_array_extraction()
         end
         return unwrap_internal_array(val)
     else
@@ -630,7 +637,7 @@ end
 function _subset_partialarray(pa::PartialArray, inds::Vararg{Any}; kw...)
     if pa.data isa GrowableArray &&
         any(ind -> ind isa AbstractPPL.DynamicIndex || ind isa Colon, inds)
-        _warn_growable_array()
+        _warn_growable_array_extraction()
     end
     new_data = view(pa.data, inds...; kw...)
     new_mask = view(pa.mask, inds...; kw...)
@@ -783,7 +790,7 @@ function unwrap_internal_array(pa::PartialArray)
 
     retval = pa.data
     if retval isa GrowableArray
-        _warn_growable_array()
+        _warn_growable_array_extraction()
     end
     if eltype(retval) <: ArrayLikeBlock || ArrayLikeBlock <: eltype(retval)
         for ind in eachindex(retval)
@@ -801,12 +808,23 @@ function unwrap_internal_array(pa::PartialArray)
 end
 unwrap_internal_array(ga::GrowableArray) = ga.data
 
-function _warn_growable_array()
+function _warn_growable_array_extraction()
     @warn (
         "Returning a `Base.Array` with a presumed size based on the indices" *
-        " used to set values; but this may not be the actual shape or size" *
+        " used to set values; but this may not be the actual type or size" *
         " of the actual `AbstractArray` that was inside the DynamicPPL model." *
         " You should inspect the returned result to make sure that it has the" *
-        " correct value."
+        " correct value.\n\n" *
+        "To find out how to avoid this warning, please see: " *
+        "https://turinglang.org/docs/uri/growablearray"
+    )
+end
+function _warn_growable_array_creation(size)
+    @warn (
+        "Creating a growable `Base.Array` of dimension $(length(size)) to store" *
+        " values. This may not match the actual type or size of the actual" *
+        " `AbstractArray` that will be used inside the DynamicPPL model.\n\n" *
+        " If this is not the type or size that you expect, please see:" *
+        " https://turinglang.org/docs/uri/growablearray"
     )
 end

test/varnamedtuple.jl

@@ -2,7 +2,7 @@ module VarNamedTupleTests
 
 using Combinatorics: Combinatorics
 using OrderedCollections: OrderedDict
-using Test: @inferred, @test, @test_throws, @testset, @test_broken
+using Test: @inferred, @test, @test_throws, @testset, @test_broken, @test_logs
 using DynamicPPL: DynamicPPL, @varname, VarNamedTuple, subset
 using DynamicPPL.VarNamedTuples:
     PartialArray,
@@ -643,25 +643,42 @@ Base.size(st::SizedThing) = st.size
             end
         end
 
+        @testset "Warning when setting untemplated values" begin
+            warnmsg = r"Creating a growable `Base.Array`"
+            @test_logs (:warn, warnmsg) vnt = setindex!!(
+                VarNamedTuple(), [1.0, 2.0], @varname(x[1:2])
+            )
+            @test_logs (:warn, warnmsg) vnt = setindex!!(
+                VarNamedTuple(), 1.0, @varname(x[1])
+            )
+            @test_logs (:warn, warnmsg) vnt = setindex!!(
+                VarNamedTuple(), 1.0, @varname(x[2])
+            )
+            # This shouldn't warn, because `x` is just the whole vector
+            @test_logs vnt = setindex!!(VarNamedTuple(), [1.0, 2.0], @varname(x))
+            # With a template it shouldn't warn
+            @test_logs vnt = templated_setindex!!(
+                VarNamedTuple(), 1.0, @varname(x[1]), zeros(2)
+            )
+        end
+
         @testset "Warning when trying to extract values" begin
             vnt = @vnt begin
                 x[1] := 1.0
                 x[2] := 2.0
             end
             warnmsg = r"Returning a `Base.Array` with"
-            # These should warn
+            # These should warn. There are various calls to _warn_growable_array() inside
+            # the VNT code to handle each of these cases.
             @test_logs (:warn, warnmsg) vnt[@varname(x[:][1])]
             @test_logs (:warn, warnmsg) vnt[@varname(x[:])]
             @test_logs (:warn, warnmsg) vnt[@varname(x)]
-            # These shouldn't warn
+            @test_logs (:warn, warnmsg) vnt[@varname(x[begin])]
+            @test_logs (:warn, warnmsg) vnt[@varname(x[end])]
+            @test_logs (:warn, warnmsg) vnt[@varname(x[1:end])]
+            # These shouldn't warn because they are safe
             @test_logs vnt[@varname(x[1:2])]
             @test_logs vnt[@varname(x[1])]
-            # The following with DynamicIndex things are broken. They should warn, but
-            # currently they don't because by the time you try to index into the
-            # GrowableArray, the indices are already concretised. This can be fixed.
-            @test_broken false
-            @test_logs vnt[@varname(x[end])]
-            @test_logs vnt[@varname(x[1:end])]
         end
     end