[TS] Correctly resolve type references for TypeScriptTaggedUnion (#4380)

Author: MangelMaxime

src/Fable.Cli/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* [TS] Correctly resolve type references for `TypeScriptTaggedUnion` (by @MangelMaxime and @jrwone0)
 * [TS] Expose optional `stack` property on `Exception` (by @MangelMaxime)
 * [Python] Fix `nonlocal`/`global` declarations generated inside `match/case` bodies causing `SyntaxError` (by @dbrattli)
 * [Python] Fix exception variable captured in deferred closures causing `NameError` (PEP 3110 scoping) (by @dbrattli)

src/Fable.Compiler/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* [TS] Correctly resolve type references for `TypeScriptTaggedUnion` (by @MangelMaxime and @jrwone0)
 * [Python] Fix `nonlocal`/`global` declarations generated inside `match/case` bodies causing `SyntaxError` (by @dbrattli)
 * [Python] Fix exception variable captured in deferred closures causing `NameError` (PEP 3110 scoping) (by @dbrattli)
 

src/Fable.Transforms/FSharp2Fable.fs

@@ -96,13 +96,16 @@ let private transformNewUnion com ctx r fsType (unionCase: FSharpUnionCase) (arg
 
                 let fieldTypes = makeTypeGenArgs ctx.GenericArgs fieldTypes
 
-                Fable.NewAnonymousRecord(
-                    tagExpr :: argExprs,
-                    Array.append [| tagName |] fieldNames,
-                    tagExpr.Type :: fieldTypes,
-                    false
-                )
-                |> makeValue r
+                let expr =
+                    Fable.NewAnonymousRecord(
+                        tagExpr :: argExprs,
+                        Array.append [| tagName |] fieldNames,
+                        tagExpr.Type :: fieldTypes,
+                        false
+                    )
+                    |> makeValue r
+
+                Fable.TypeCast(expr, makeType ctx.GenericArgs fsType)
 
     | StringEnum(tdef, rule) ->
         match argExprs with

tests/Js/Main/JsInteropTests.fs

@@ -339,6 +339,17 @@ module TaggedUnion =
         | [<CompiledValue(Kind.Bar)>] Bar of Bar<Kind>
         | [<CompiledValue(Kind.Baz)>] Baz of Baz<Kind>
 
+
+    [<RequireQualifiedAccess>]
+    [<TypeScriptTaggedUnion("type")>]
+    type SimpleFoo =
+        | Bar of baz: int
+
+    [<RequireQualifiedAccess>]
+    [<TypeScriptTaggedUnion("type")>]
+    type FooGeneric<'a> =
+        | Bar of baz: 'a
+
 #if FABLE_COMPILER
 module PojoDefinedByConsArgs =
     [<JS.Pojo; AllowNullLiteral>]
@@ -960,6 +971,28 @@ let tests =
         TaggedUnion.EnumTagged.Foo !!{| kind = TaggedUnion.Kind.Foo; foo = "hello" |} |> describe |> equal "foo: hello"
         TaggedUnion.EnumTagged.Bar !!{| kind = TaggedUnion.Kind.Bar; bar = 42 |} |> describe |> equal "bar: 42"
         TaggedUnion.EnumTagged.Baz !!{| kind = TaggedUnion.Kind.Baz; baz = false |} |> describe |> equal "baz: false"
+
+    // Fix https://github.com/fable-compiler/Fable/issues/4378
+    testCase "TypeScriptTaggedUnion produce the correct return type for a function" <| fun () ->
+        let getFoo (baz: int) =
+            (TaggedUnion.SimpleFoo.Bar baz)
+
+        let foo = getFoo 10
+
+        equal (TaggedUnion.SimpleFoo.Bar 10) foo
+
+    testCase "TypeScriptTaggedUnion produce the correct type for a value" <| fun () ->
+        let foo1 = TaggedUnion.SimpleFoo.Bar 10
+
+        equal (TaggedUnion.SimpleFoo.Bar 10) foo1
+
+    testCase "TypeScriptTaggedUnion produce the type even with generic type parameters" <| fun () ->
+        let getFooGeneric (baz: 'a) : TaggedUnion.FooGeneric<'a> =
+            (TaggedUnion.FooGeneric.Bar baz)
+
+        let fooGeneric = getFooGeneric 10
+
+        equal (TaggedUnion.FooGeneric.Bar 10) fooGeneric
 #endif
 
     testCase "Pattern matching with StringEnum works" <| fun () ->