From 32fefb1f35963dd97a1de42cd37c2025e0031ecc Mon Sep 17 00:00:00 2001
From: Ruben Bartelink <ruben@bartelink.com>
Date: Mon, 25 May 2020 16:10:26 +0100
Subject: [PATCH] UnionConverter: Accept custom discriminator without
 catchAllCase (#51)

---
 CHANGELOG.md                                  |  2 ++
 src/FsCodec.NewtonsoftJson/UnionConverter.fs  |  5 +++--
 .../UnionConverterTests.fs                    | 20 +++++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f5a1a44..b908d14 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,8 @@ The `Unreleased` section name is replaced by the expected version of next releas
 ### Removed
 ### Fixed
 
+- `UnionConverter`: Support overriding discriminator without needing to nominate a `catchAllCase` [#51](https://github.com/jet/FsCodec/pull/51)
+
 <a name="2.1.0"></a>
 ## [2.1.0] - 2020-05-10
 
diff --git a/src/FsCodec.NewtonsoftJson/UnionConverter.fs b/src/FsCodec.NewtonsoftJson/UnionConverter.fs
index f9e9b20..4cc4ebd 100755
--- a/src/FsCodec.NewtonsoftJson/UnionConverter.fs
+++ b/src/FsCodec.NewtonsoftJson/UnionConverter.fs
@@ -72,8 +72,9 @@ module private Union =
 type UnionConverter private (discriminator : string, ?catchAllCase) =
     inherit JsonConverter()
 
-    new() = UnionConverter("case")
-    new(discriminator: string, catchAllCase: string) = UnionConverter(discriminator, ?catchAllCase = match catchAllCase with null -> None | x -> Some x)
+    new() = UnionConverter("case", ?catchAllCase=None)
+    new(discriminator: string) = UnionConverter(discriminator, ?catchAllCase=None)
+    new(discriminator: string, catchAllCase: string) = UnionConverter(discriminator, ?catchAllCase=match catchAllCase with null -> None | x -> Some x)
 
     override __.CanConvert (t : Type) = Union.isUnion t
 
diff --git a/tests/FsCodec.NewtonsoftJson.Tests/UnionConverterTests.fs b/tests/FsCodec.NewtonsoftJson.Tests/UnionConverterTests.fs
index 6a85282..870135b 100644
--- a/tests/FsCodec.NewtonsoftJson.Tests/UnionConverterTests.fs
+++ b/tests/FsCodec.NewtonsoftJson.Tests/UnionConverterTests.fs
@@ -297,6 +297,26 @@ let ``Implementation ensures no internal errors escape (which would render a Web
     test <@ (CaseD "hi") = d @>
     test <@ false = gotError @>
 
+module CustomDiscriminator =
+
+    [<JsonConverter(typeof<UnionConverter>, "esac")>]
+    type DuWithCustomDiscriminator =
+        | Known
+        | Catchall
+
+    [<Fact>]
+    let ``UnionConverter handles custom discriminator`` () =
+        let json = """{"esac":"Known"}"""
+        test <@ DuWithCustomDiscriminator.Known = JsonConvert.DeserializeObject<_> json @>
+
+    [<Fact>]
+    let ``UnionConverter can complain about missing case with custom discriminator without catchall`` () =
+        let aJson = """{"esac":"CaseUnknown"}"""
+        let act () = JsonConvert.DeserializeObject<DuWithCustomDiscriminator>(aJson, settings)
+
+        fun (e : System.InvalidOperationException) -> <@ -1 <> e.Message.IndexOf "No case defined for 'CaseUnknown', and no catchAllCase nominated" @>
+        |> raisesWith <@ act() @>
+
 module ``Unmatched case handling`` =
 
     [<Fact>]