Bug: Unexpected sign for large int64 decoding.

[travis-leith]

open Thoth.Json.Net

type test_type = { i: int64 }

let extra = Extra.empty |> Extra.withInt64
let test_type_decoder = Decode.Auto.generateDecoder<test_type> (extra = extra)

let test_type_json1 = """{"i": 9223372036854775806}"""
let test_type_json2 = """{"i": 8223372036854775806}"""

let test_type1 = Decode.Auto.fromString<test_type> (test_type_json1, extra = extra)

let test_type2 = Decode.fromString test_type_decoder test_type_json2

printfn "test_type1: %A" test_type1
printfn "test_type2: %A" test_type2

For some reason the first value gets parsed as -ve. This seems to only happen for numbers close to the max value. Maybe some sort of overflow is happening.

[travis-leith]

I found this bug by making sure that Decode.Auto.fromString works the same way as Decode.Auto.generateDecoder, if you are wondering why I use 2 different techniques here.

[MangelMaxime]

Thank you for the report, I will investigate this issue while working on porting the Auto API to the new API.

[njlr]

This does not appear to be an issue in Thoth.Json.Core.Auto:

#r "nuget: Thoth.Json.Core, 0.9.0"
#r "nuget: Thoth.Json.Core.Auto, 0.1.0"
#r "nuget: Thoth.Json.System.Text.Json, 0.3.0"

open Thoth.Json.Core.Auto
open Thoth.Json.System.Text.Json

type test_type = { i: int64 }

let extra = Extra.empty |> Extra.withInt64
let test_type_decoder = Decode.Auto.generateDecoder<test_type> (extra = extra)

let test_type_json1 = """{"i": 9223372036854775806}"""
let test_type_json2 = """{"i": 8223372036854775806}"""

let test_type1 = Decode.fromString test_type_decoder test_type_json1
let test_type2 = Decode.fromString test_type_decoder test_type_json2

printfn "test_type1: %A" test_type1
printfn "test_type2: %A" test_type2

test_type1: Ok { i = 9223372036854775807L }
test_type2: Ok { i = 8223372036854775808L }

1. Decode.Auto.fromString no longer exists
2. Both numbers come back positive

Edit:

The numbers are slightly off? 🤔

9223372036854775806
9223372036854775807

8223372036854775806
8223372036854775808

We see the same behavior with an explicitly defined decoder:

let test_type_decoder = Decode.field "i" Decode.int64

test_type1: Ok 9223372036854775807L
test_type2: Ok 8223372036854775808L

This is expected since the new Auto module only uses reflection to compose the simple decoders.

[MangelMaxime]

I was going to ask if it was related to Fable, but your example is actually for .NET 😱