Try #394:

Author: bors[bot]

Project.toml

@@ -1,6 +1,6 @@
 name = "DynamicPPL"
 uuid = "366bfd00-2699-11ea-058f-f148b4cae6d8"
-version = "0.17.9"
+version = "0.17.10"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"

src/compiler.jl

@@ -245,6 +245,9 @@ function build_model_info(input_expr)
         return modelinfo
     end
 
+    # Ensure that all arguments have a name, i.e., are of the form `name` or `name::T`
+    addargnames!(modeldef[:args])
+
     # Extract the positional and keyword arguments from the model definition.
     allargs = vcat(modeldef[:args], modeldef[:kwargs])
 
@@ -262,8 +265,7 @@ function build_model_info(input_expr)
     # Extract the names of the arguments.
     allargs_syms = map(allargs_exprs) do arg
         MacroTools.@match arg begin
-            (::Type{T_}) | (name_::Type{T_}) => T
-            name_::T_ => name
+            (name_::_) => name
             x_ => x
         end
     end

src/utils.jl

@@ -74,6 +74,48 @@ macro addlogprob!(ex)
     end
 end
 
+"""
+    addargnames!(args)
+
+Adds names to unnamed arguments in `args`.
+
+The names are generated with `gensym(:arg)` to avoid conflicts with other variable names.
+
+# Examples
+
+```jldoctest; filter = r"var\\"##arg#[0-9]+\\""
+julia> args = :(f(x::Int, y, ::Type{T}=Float64)).args[2:end]
+3-element Vector{Any}:
+ :(x::Int)
+ :y
+ :($(Expr(:kw, :(::Type{T}), :Float64)))
+
+julia> DynamicPPL.addargnames!(args)
+
+julia> args
+3-element Vector{Any}:
+ :(x::Int)
+ :y
+ :($(Expr(:kw, :(var"##arg#301"::Type{T}), :Float64)))
+```
+"""
+function addargnames!(args)
+    if isempty(args)
+        return nothing
+    end
+
+    @inbounds for i in eachindex(args)
+        arg = args[i]
+        if MacroTools.@capture(arg, ::T_)
+            args[i] = Expr(:(::), gensym(:arg), T)
+        elseif MacroTools.@capture(arg, ::T_ = val_)
+            args[i] = Expr(:kw, Expr(:(::), gensym(:arg), T), val)
+        end
+    end
+
+    return nothing
+end
+
 """
     getargs_dottilde(x)
 

test/compiler.jl

@@ -602,4 +602,10 @@ end
         @test !DynamicPPL.hasmissing(Matrix{Real})
         @test !DynamicPPL.hasmissing(Vector{Matrix{Float32}})
     end
+
+    @testset "issue #393: anonymous argument with type parameter" begin
+        @model f_393(::Val{ispredict}=Val(false)) where {ispredict} = ispredict ? 0 : 1
+        @test f_393()() == 1
+        @test f_393(Val(true))() == 0
+    end
 end