Add @auto macro to automatically provide StructTypes definitions for a type tree

src/macros.jl

@@ -5,7 +5,7 @@
         """
             @$(isolate_name($struct_type))(expr::Expr)
             @$(isolate_name($struct_type))(expr::Symbol)
-        
+
         If `expr` is a struct definition, sets the `StructType` of the defined struct to
         `$(isolate_name($struct_type))()`. If `expr` is the name of a `Type`, sets the `StructType` of that
         type to `$(isolate_name($struct_type))()`.
@@ -18,7 +18,7 @@
         ```julia
         StructTypes.StructType(::Type{MyStruct}) = StructType.Struct()
         ```
-        and 
+        and
         ```julia
         @$(isolate_name($struct_type)) struct MyStruct
             val::Int
@@ -59,7 +59,7 @@
 
 """
 Macro to add subtypes for an abstract type without the need for type field.
-For a given `abstract_type`` and `struct_subtype` generates custom lowered NameTuple 
+For a given `abstract_type`` and `struct_subtype` generates custom lowered NameTuple
 with all subtype fields and additional `StructTypes.subtypekey` field
 used for identifying the appropriate concrete subtype.
 
@@ -87,4 +87,68 @@
         StructTypes.lowertype(::Type{$(esc(struct_subtype))}) = @NamedTuple{$field_name::$(esc(Symbol)), $(name_types...)}
         $(esc(struct_subtype))(x::@NamedTuple{$field_name::$(esc(Symbol)), $(name_types...)}) = $(esc(struct_subtype))($(x_names...))
     end
-end
+end
+
+
+#-----------------------------------------------------------------------------# @auto
+
+
+"""
+    @auto AbstractSuperType
+    @auto AbstractSuperType _my_subtype_key_
+
+Macro to automatically generate the StructTypes interface for every subtype of `AbstractSuperType`.
+With the example of JSON3, this enables you to `JSON3.read(str, MyType)` where `MyType <: AbstractSuperType`.
+
+`@auto` assumes that all subtypes of the provided `AbstractSuperType` have the default constructors
+provided by Julia.  If this is not the case, you'll need to overload:
+
+    StructTypes.construct(::Type{MyType}, named_tuple::StructTypes.lowertype(MyType)) = MyType(...)
+
+"""
+macro auto(T, subtypekey = :__type__)
+    esc(quote
+
+        if $T isa UnionAll
+            @warn "Cannot use @auto with UnionAll types."
+        else
+            function StructTypes.StructType(::Type{T}) where {T <: $T}
+                isconcretetype(T) ? StructTypes.CustomStruct() : StructTypes.AbstractType()
+            end
+
+            function StructTypes.lower(x::T) where {T <: $T}
+                ($subtypekey = Symbol(T), NamedTuple(k => getfield(x, k) for k in fieldnames(T))...)
+            end
+
+            function StructTypes.lowertype(::Type{T}) where {T <: $T}
+                NamedTuple{($(QuoteNode(subtypekey)), fieldnames(T)...), Tuple{Symbol, fieldtypes(T)...}}
+            end
+
+            function StructTypes.construct(::Type{T}, nt::StructTypes.lowertype(Type{T})) where T <: $T
+                T((nt[x] for x in fieldnames(T))...)
+            end
+
+            function StructTypes.subtypes(::Type{T}) where {T <: $T}
+                StructTypes.SubTypeClosure() do x::Symbol
+                    e = Meta.parse(string(x))
+                    if StructTypes.is_valid_type_ex(e)
+                        try     # try needed to catch undefined symbols
+                            S = eval(e)
+                            S isa Type && S <: T && return S
+                        catch
+                        end
+                    end
+                    return Any
+                end
+            end
+
+            StructTypes.subtypekey(T::Type{<: $T}) = $(QuoteNode(subtypekey))
+        end
+    end)
+end
+
+is_valid_type_ex(x) = isbits(x)
+
+is_valid_type_ex(s::Union{Symbol, QuoteNode}) = true
+
+is_valid_type_ex(e::Expr) = ((e.head == :curly || e.head == :tuple || e.head == :.) && all(map(is_valid_type_ex, e.args)))

test/runtests.jl

@@ -23,12 +23,12 @@ end
 builtin_type_mapping = Dict(
     StructTypes.AbstractType() => Union{
         Core.IO,
-        Core.Number, 
+        Core.Number,
         Base.AbstractDisplay,
         Base.VERSION <= v"1.2" ? Union{} : Union{
             Base.AbstractMatch,
             Base.AbstractPattern,
-        } 
+        }
     },
     StructTypes.UnorderedStruct() => Union{
         Core.Any, # Might be too open
@@ -676,7 +676,7 @@ function bicycle_subtypes(t_sym::Symbol)
     isempty(t[1]) && t[2] == 1 && return Gravel # gravel bikes often have 1 x N chainring/cog setups
 end
 sub_type_closure = StructTypes.SubTypeClosure(bicycle_subtypes)
-StructTypes.subtypes(::Type{Bicycle}) = sub_type_closure 
+StructTypes.subtypes(::Type{Bicycle}) = sub_type_closure
 
 mutable struct C2
     a::Int
@@ -855,4 +855,40 @@ StructTypes.@register_struct_subtype Vehicle2 Truck2
     @test StructTypes.lowertype(Car2) === typeof(nt)
     @test typeof(car) == Car2
     @test car.make == "Mercedes-Benz"
-end
+end
+
+
+# @auto
+abstract type AbstractSuperType end
+StructTypes.@auto AbstractSuperType
+
+abstract type AbstractSubType <: AbstractSuperType end
+struct AutoA <: AbstractSuperType
+    x::Int
+    y::String
+    z::Symbol
+end
+struct AutoB <: AbstractSubType
+    x::String
+    y::Symbol
+    z::Float64
+end
+struct AutoC{T, S} <: AbstractSubType
+    x::T
+    y::S
+    z::String
+end
+
+
+@testset "@auto" begin
+    @test StructTypes.StructType(AutoC) == StructTypes.AbstractType()
+    @test StructTypes.StructType(AutoC{Int,Int}) == StructTypes.CustomStruct()
+
+    a = AutoA(1, "2", :three)
+    b = AutoB("one", :two, 3.0)
+    c = AutoC(:one, "two", "three")
+
+    @test StructTypes.construct(AutoA, StructTypes.lower(a)) == a
+    @test StructTypes.construct(AutoB, StructTypes.lower(b)) == b
+    @test StructTypes.construct(AutoC{Symbol,String}, StructTypes.lower(c)) == c
+end