TOML: fix converted tabular data printing

Previously the printing pass for converted data only works for
non-tabular data (like simple number literals), and it doesn't work for
`Dict` or `Array`s. Rather it leads to runtime error because we don't
pass over the same `by` keyword  argument through recursive calls and it
may not be assigned:
```julia
julia> struct MyStruct
           a::Int
       end

julia> data = Dict(:foo => MyStruct(1))
Dict{Symbol, MyStruct} with 1 entry:
  :foo => MyStruct(1)

julia> TOML.print(data; softed=true) do x
           x isa MyStruct && return Dict(:bar => x.a)
       end
ERROR: MethodError: no method matching print(::var"#38#39", ::Dict{Symbol, MyStruct}; softed=true)
You may have intended to import Base.print
Closest candidates are:
  print(::Union{Nothing, Function}, ::AbstractDict; sorted, by) at /Users/aviatesk/julia/julia/stdlib/TOML/src/print.jl:130 got unsupported keyword argument "softed"
  print(::Union{Nothing, Function}, ::IO, ::AbstractDict; sorted, by) at /Users/aviatesk/julia/julia/stdlib/TOML/src/print.jl:129 got unsupported keyword argument "softed"
  print(::IO, ::AbstractDict; sorted, by) at /Users/aviatesk/julia/julia/stdlib/TOML/src/print.jl:131 got unsupported keyword argument "softed"
Stacktrace:
 [1] kwerr(::NamedTuple{(:softed,), Tuple{Bool}}, ::Function, ::Function, ::Dict{Symbol, MyStruct})
   @ Base ./error.jl:163
 [2] top-level scope
   @ none:1
```

<details><summary>Originally reported by JET:</summary>
julia> using JET, Pkg

julia> @report_call Pkg.project()
═════ 3 possible errors found ═════
┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/API.jl:103 Pkg.API.EnvCache()
│┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/Types.jl:285 #self#(Pkg.Types.nothing)
││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/Types.jl:288 Pkg.Types.read_project(project_file)
│││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/project.jl:138 Pkg.Types.sprint(Pkg.Types.showerror, e)
││││┌ @ strings/io.jl:106 Base.#sprint#412(Core.tuple(Base.nothing, 0, #self#, f), args...)
│││││┌ @ strings/io.jl:112 f(Core.tuple(s), args...)
││││││┌ @ toml_parser.jl:326 Base.TOML.point_to_line(Base.getproperty(err, :str), pos, pos, io)
│││││││ for 1 of union split cases, no matching method found for call signatures (Tuple{typeof(Base.TOML.point_to_line), Nothing, Int64, Int64, IOBuffer})): Base.TOML.point_to_line(Base.getproperty(err::Base.TOML.ParserError, :str::Symbol)::Union{Nothing, String}, pos::Int64, pos::Int64, io::IOBuffer)
││││││└──────────────────────
│││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/project.jl:142 Pkg.Types.Project(raw)
││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/project.jl:124 Base.setproperty!(project, :targets, Pkg.Types.read_project_targets(Pkg.Types.get(raw, "targets", Pkg.Types.nothing), project))
│││││┌ @ Base.jl:35 Base.convert(Base.fieldtype(Base.typeof(x), f), v)
││││││┌ @ abstractdict.jl:523 _(x)
│││││││┌ @ dict.jl:104 Base.setindex!(h, v, k)
││││││││┌ @ dict.jl:382 Base.convert(_, v0)
│││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/LinearAlgebra/src/factorization.jl:58 _(f)
││││││││││ no matching method found for call signature (Tuple{Type{Vector{String}}, LinearAlgebra.Factorization}): _::Type{Vector{String}}(f::LinearAlgebra.Factorization)
│││││││││└─────────────────────────────────────────────────────────────────────────────────────────────────
││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/Types.jl:305 Pkg.Types.write_env_usage(manifest_file, "manifest_usage.toml")
│││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/Types.jl:436 Pkg.Types.sprint(#35)
││││┌ @ strings/io.jl:106 Base.#sprint#412(Core.tuple(Base.nothing, 0, #self#, f), args...)
│││││┌ @ strings/io.jl:112 f(Core.tuple(s), args...)
││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/Pkg/src/Types.jl:437 TOML.print(io, Pkg.Types.Dict(Pkg.Types.=>(Core.getfield(#self#, :source_file), Base.vect(Pkg.Types.Dict(Pkg.Types.=>("time", Pkg.Types.now()))))))
│││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:131 TOML.Internals.Printer.#print#16(false, TOML.Internals.Printer.identity, #self#, io, a)
││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:131 Core.kwfunc(TOML.Internals.Printer._print)(Core.apply_type(Core.NamedTuple, (:sorted, :by))(Core.tuple(sorted, by)), TOML.Internals.Printer._print, TOML.Internals.Printer.nothing, io, a)
│││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:76 #s848(_2, _3, f, io, a, Base.getindex(TOML.Internals.Printer.String))
││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:76 TOML.Internals.Printer.#_print#11(indent, first_block, sorted, by, _3, f, io, a, ks)
│││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:88 Core.kwfunc(TOML.Internals.Printer.printvalue)(Core.apply_type(Core.NamedTuple, (:sorted,))(Core.tuple(sorted)), TOML.Internals.Printer.printvalue, f, io, value)
││││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:25 TOML.Internals.Printer.#printvalue#1(sorted, _3, f, io, value)
│││││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:29 Core.kwfunc(TOML.Internals.Printer._print)(Core.apply_type(Core.NamedTuple, (:sorted,))(Core.tuple(sorted)), TOML.Internals.Printer._print, f, io, x)
││││││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:76 #s848(_2, _3, f, io, a, Base.getindex(TOML.Internals.Printer.String))
│││││││││││││││┌ @ /Users/aviatesk/julia/julia/usr/share/julia/stdlib/v1.7/TOML/src/print.jl:76 Core.throw(Core.UndefKeywordError(:by))
││││││││││││││││ UndefKeywordError: keyword argument by not assigned
│││││││││││││││└────────────────────────────────────────────────────────────────────────────────
Pkg.API.ProjectInfo
</details>

With this PR, everything should work:
> After
```julia
julia> TOML.print(data; sorted=true) do x
           x isa MyStruct && return Dict(:bar => x.a)
       end
[foo]
bar = 1
```

Author: aviatesk

stdlib/TOML/src/print.jl

@@ -2,6 +2,7 @@
 
 import Dates
 
+import Base: @invokelatest
 import ..isvalid_barekey_char
 
 function printkey(io::IO, keys::Vector{String})
@@ -20,46 +21,36 @@ function printkey(io::IO, keys::Vector{String})
 end
 
 const MbyFunc = Union{Function, Nothing}
-const TOMLValue = Union{AbstractVector, AbstractDict, Dates.DateTime, Dates.Time, Dates.Date, Bool, Integer, AbstractFloat, String}
-function printvalue(f::MbyFunc, io::IO, value::AbstractVector; sorted=false)
+const TOMLValue = Union{AbstractVector, AbstractDict, Dates.DateTime, Dates.Time, Dates.Date, Bool, Integer, AbstractFloat, AbstractString}
+function printvalue(f::MbyFunc, io::IO, value::AbstractVector; sorted=false, by=identity)
     Base.print(io, "[")
     for (i, x) in enumerate(value)
         i != 1 && Base.print(io, ", ")
         if isa(x, AbstractDict)
-            _print(f, io, x; sorted)
+            _print(f, io, x; sorted, by)
         else
-            printvalue(f, io, x; sorted)
+            printvalue(f, io, x; sorted, by)
         end
     end
     Base.print(io, "]")
 end
-function printvalue(f::MbyFunc, io::IO, value; sorted)
-    if f === nothing
-        error("type `$(typeof(value))` is not a valid TOML type, pass a conversion function to `TOML.print`")
-    end
-    toml_value = f(value)
-    if !(toml_value isa TOMLValue)
-        error("TOML syntax function for type `$(typeof(value))` did not return a valid TOML type but a `$(typeof(toml_value))`")
-    end
-    Base.invokelatest(printvalue, f, io, toml_value; sorted)
-end
-printvalue(f::MbyFunc, io::IO, value::AbstractDict; sorted) =
-    _print(f, io, value; sorted)
-printvalue(f::MbyFunc, io::IO, value::Dates.DateTime; sorted) =
+printvalue(f::MbyFunc, io::IO, value::AbstractDict; sorted=false, by=identity) =
+    _print(f, io, value; sorted, by)
+printvalue(f::MbyFunc, io::IO, value::Dates.DateTime; _...) =
     Base.print(io, Dates.format(value, Dates.dateformat"YYYY-mm-dd\THH:MM:SS.sss\Z"))
-printvalue(f::MbyFunc, io::IO, value::Dates.Time; sorted) =
+printvalue(f::MbyFunc, io::IO, value::Dates.Time; _...) =
     Base.print(io, Dates.format(value, Dates.dateformat"HH:MM:SS.sss"))
-printvalue(f::MbyFunc, io::IO, value::Dates.Date; sorted) =
+printvalue(f::MbyFunc, io::IO, value::Dates.Date; _...) =
     Base.print(io, Dates.format(value, Dates.dateformat"YYYY-mm-dd"))
-printvalue(f::MbyFunc, io::IO, value::Bool; sorted) =
+printvalue(f::MbyFunc, io::IO, value::Bool; _...) =
     Base.print(io, value ? "true" : "false")
-printvalue(f::MbyFunc, io::IO, value::Integer; sorted) =
+printvalue(f::MbyFunc, io::IO, value::Integer; _...) =
     Base.print(io, Int64(value))  # TOML specifies 64-bit signed long range for integer
-printvalue(f::MbyFunc, io::IO, value::AbstractFloat; sorted) =
+printvalue(f::MbyFunc, io::IO, value::AbstractFloat; _...) =
     Base.print(io, isnan(value) ? "nan" :
                    isinf(value) ? string(value > 0 ? "+" : "-", "inf") :
                    Float64(value))  # TOML specifies IEEE 754 binary64 for float
-printvalue(f::MbyFunc, io::IO, value::AbstractString; sorted) = Base.print(io, "\"", escape_string(value), "\"")
+printvalue(f::MbyFunc, io::IO, value::AbstractString; _...) = Base.print(io, "\"", escape_string(value), "\"")
 
 is_table(value)           = isa(value, AbstractDict)
 is_array_of_tables(value) = isa(value, AbstractArray) &&
@@ -70,8 +61,8 @@ function _print(f::MbyFunc, io::IO, a::AbstractDict,
     ks::Vector{String} = String[];
     indent::Int = 0,
     first_block::Bool = true,
-    sorted::Bool,
-    by::Function,
+    sorted::Bool = false,
+    by::Function = identity,
 )
     akeys = keys(a)
     if sorted
@@ -82,11 +73,25 @@ function _print(f::MbyFunc, io::IO, a::AbstractDict,
     for key in akeys
         value = a[key]
         is_tabular(value) && continue
-        Base.print(io, ' '^4max(0,indent-1))
-        printkey(io, [String(key)])
-        Base.print(io, " = ") # print separator
-        printvalue(f, io, value; sorted)
-        Base.print(io, "\n")  # new line?
+        if !isa(value, TOMLValue)
+            if f === nothing
+                error("type `$(typeof(value))` is not a valid TOML type, pass a conversion function to `TOML.print`")
+            end
+            toml_value = f(value)
+            if !(toml_value isa TOMLValue)
+                error("TOML syntax function for type `$(typeof(value))` did not return a valid TOML type but a `$(typeof(toml_value))`")
+            end
+            value = toml_value
+        end
+        if is_tabular(value)
+            _print(f, io, Dict(key => value); indent, first_block, sorted, by)
+        else
+            Base.print(io, ' '^4max(0,indent-1))
+            printkey(io, [String(key)])
+            Base.print(io, " = ") # print separator
+            printvalue(f, io, value; sorted, by)
+            Base.print(io, "\n")  # new line?
+        end
         first_block = false
     end
 
@@ -105,7 +110,7 @@ function _print(f::MbyFunc, io::IO, a::AbstractDict,
                 Base.print(io,"]\n")
             end
             # Use runtime dispatch here since the type of value seems not to be enforced other than as AbstractDict
-            Base.invokelatest(_print, f, io, value, ks; indent = indent + header, first_block = header, sorted, by)
+            @invokelatest _print(f, io, value, ks; indent = indent + header, first_block = header, sorted, by)
             pop!(ks)
         elseif is_array_of_tables(value)
             # print array of tables
@@ -119,7 +124,7 @@ function _print(f::MbyFunc, io::IO, a::AbstractDict,
                 Base.print(io,"]]\n")
                 # TODO, nicer error here
                 !isa(v, AbstractDict) && error("array should contain only tables")
-                Base.invokelatest(_print, f, io, v, ks; indent = indent + 1, sorted, by)
+                @invokelatest _print(f, io, v, ks; indent = indent + 1, sorted, by)
             end
             pop!(ks)
         end

stdlib/TOML/test/print.jl

@@ -21,12 +21,34 @@ struct MyStruct
     a::Int
 end
 @test_throws ErrorException toml_str(Dict("foo" => MyStruct(1)))
+# simple value
 @test toml_str(Dict("foo" => MyStruct(1))) do x
         x isa MyStruct && return x.a
     end == """
         foo = 1
         """
 
+# tabular values
+@test toml_str(Dict("foo" => MyStruct(1)); sorted=true) do x
+         x isa MyStruct && return [x.a]
+     end == """
+         foo = [1]
+         """
+@test toml_str(Dict("foo" => MyStruct(1)); sorted=true) do x
+        x isa MyStruct && return Dict(:bar => x.a)
+    end == """
+        [foo]
+        bar = 1
+        """
+
+# validation against the usual case
+@test toml_str(Dict("foo" => MyStruct(1)); sorted=true) do x
+         x isa MyStruct && return [x.a]
+     end == toml_str(Dict("foo" => [1]); sorted=true)
+@test toml_str(Dict("foo" => MyStruct(1)); sorted=true) do x
+        x isa MyStruct && return Dict(:bar => x.a)
+    end == toml_str(Dict("foo" => Dict(:bar => 1)); sorted=true)
+
 @test toml_str(Dict("b" => SubString("foo"))) == "b = \"foo\"\n"
 
 @testset "empty dict print" begin