fix(parse): forward type predicates to inner style (#454)

JSONReadStyle wraps the user-provided style for null/dicttype/unknown_fields config, but
StructUtils dispatches on the wrapping JSONReadStyle. As a result, methods like
dictlike(::CustomJSONStyle, ::Type{A}) defined on a user JSONStyle never fired during
parsing — make() fell through to makestruct instead of makedict.

Forward dictlike, arraylike, and nulllike from JSONReadStyle to its inner st.style so
user-defined dispatches on a custom JSONStyle reach the StructUtils make() router.

Closes #453

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: quinnj

src/parse.jl

@@ -171,6 +171,11 @@ nullvalue(st::JSONReadStyle) = st.null
 StructUtils.fieldtagkey(::JSONStyle) = :json
 StructUtils.defaultstate(st::JSONReadStyle) = StructUtils.defaultstate(st.style)
 
+# forward StructUtils API to the inner style so user-provided JSONStyle dispatches are honored
+StructUtils.dictlike(st::JSONReadStyle, ::Type{T}) where {T} = StructUtils.dictlike(st.style, T)
+StructUtils.arraylike(st::JSONReadStyle, ::Type{T}) where {T} = StructUtils.arraylike(st.style, T)
+StructUtils.nulllike(st::JSONReadStyle, ::Type{T}) where {T} = StructUtils.nulllike(st.style, T)
+
 function jsonreadstyle(::Type{T}, ::Type{O}, null, style::StructStyle, unknown_fields::Symbol) where {T,O}
     ignore_unknown_fields =
         unknown_fields === :ignore ? true :

test/parse.jl

@@ -227,6 +227,15 @@ end
     any::Any &(choosetype=x -> x.type[] == "int" ? @NamedTuple{type::String, value::Int} : x.type[] == "float" ? @NamedTuple{type::String, value::Float64} : @NamedTuple{type::String, value::String},)
 end
 
+# https://github.com/JuliaIO/JSON.jl/issues/453 - custom JSONStyle dictlike dispatch
+@kwdef struct DictlikeViaCustomStyle
+    vals::Dict{String,Int} = Dict{String,Int}()
+end
+Base.keytype(::DictlikeViaCustomStyle) = String
+Base.valtype(::DictlikeViaCustomStyle) = Int
+StructUtils.addkeyval!(a::DictlikeViaCustomStyle, k, v) = StructUtils.addkeyval!(a.vals, k, v)
+StructUtils.dictlike(::CustomJSONStyle, ::Type{DictlikeViaCustomStyle}) = true
+
 @testset "JSON.parse" begin
     @testset "errors" begin
         # Unexpected character in array
@@ -765,6 +774,10 @@ end
     JSON.lift(::CustomJSONStyle, ::Type{Rational}, x) = Rational(x.num[], x.den[])
     @test JSON.parse("{\"num\": 1,\"den\":3}", Rational; style=CustomJSONStyle()) == 1//3
     @test JSON.parse("{\"num\": 1,\"den\":3}", Rational; style=CustomJSONStyle(), unknown_fields=:error) == 1//3
+    # https://github.com/JuliaIO/JSON.jl/issues/453 - dictlike dispatch on custom JSONStyle must reach user method
+    let res = JSON.parse("""{"a": 1, "b": 2}""", DictlikeViaCustomStyle; style=CustomJSONStyle())
+        @test res.vals == Dict("a" => 1, "b" => 2)
+    end
     @test isequal(JSON.parse("{\"num\": 1,\"den\":null}", @NamedTuple{num::Int, den::Union{Int, Missing}}; null=missing, style=StructUtils.DefaultStyle()), (num=1, den=missing))
     # choosetype field tag on Any struct field
     @test JSON.parse("{\"id\":1,\"any\":{\"type\":\"int\",\"value\":10}}", Q) == Q(1, (type="int", value=10))