[Enhancement] StringEnum can opt-in to respect CompiledValueAttribute's on cases

src/Fable.Core/Fable.Core.Types.fs

@@ -96,8 +96,24 @@ type EmitIndexerAttribute() =
 type EmitPropertyAttribute(propertyName: string) =
     inherit Attribute()
 
+/// <summary>
 /// Compile union types as string literals.
-/// More info: https://fable.io/docs/communicate/js-from-fable.html#stringenum-attribute
+/// </summary>
+/// <remarks>
+/// You can also use <c>[&lt;CompiledName>]</c> and <c>[&lt;CompiledValue>]</c> to
+/// specify the name or literal of the union case in the generated code:
+/// <code lang="fsharp">
+/// [&lt;StringEnum>]
+/// type EventType =
+///     | [&lt;CompiledName("Abracadabra")>] MouseOver
+///     | [&lt;CompiledValue(false)>] RealMagic
+/// let eventType = EventType.MouseOver // Compiles: "Abracadabra"
+/// let magicPower = EventType.RealMagic // Compiles: false
+/// </code>
+/// </remarks>
+/// <seealso href="https://fable.io/docs/javascript/features.html#caserules">
+/// Fable Documentation
+/// </seealso>
 [<AttributeUsage(AttributeTargets.Class)>]
 type StringEnumAttribute(caseRules: CaseRules) =
     inherit Attribute()

src/Fable.Transforms/FSharp2Fable.Util.fs

@@ -937,12 +937,14 @@ module Helpers =
         with _ ->
             failwith $"Cannot find case %s{unionCase.Name} in %s{FsEnt.FullName ent}"
 
-    /// Apply case rules to case name if there's no explicit compiled name
+    /// Apply case rules to case name if there's no explicit compiled name or compiled value
     let transformStringEnum (rule: CaseRules) (unionCase: FSharpUnionCase) =
-        match FsUnionCase.CompiledName unionCase with
-        | Some name -> name
-        | None -> Naming.applyCaseRule rule unionCase.Name
-        |> makeStrConst
+        match FsUnionCase.CompiledName unionCase, FsUnionCase.CompiledValue unionCase with
+        | Some name, _ -> name |> makeStrConst
+        | _, Some(CompiledValue.Boolean value) -> makeBoolConst value
+        | _, Some(CompiledValue.Float value) -> makeFloatConst value
+        | _, Some(CompiledValue.Integer value) -> makeIntConst value
+        | _ -> Naming.applyCaseRule rule unionCase.Name |> makeStrConst
 
     // let isModuleMember (memb: FSharpMemberOrFunctionOrValue) =
     //     match memb.DeclaringEntity with

tests/Js/Main/JsInteropTests.fs

@@ -225,6 +225,18 @@ type LowerAllOptions =
     | ContentBox
     | BorderBox
 
+type RespectValuesEnum = Foo = 0 | Bar = 1 | Baz = 2
+
+[<StringEnum(CaseRules.LowerAll); RequireQualifiedAccess>]
+type RespectValues =
+    | ContentBox
+    | [<CompiledValue(false)>] None
+    | [<CompiledValue(42)>] AnswerToLife
+    | [<CompiledValue(3.14159)>] Pi
+    | [<CompiledValue(RespectValuesEnum.Foo)>] Foo
+    | [<CompiledName("Bar"); CompiledValue(1)>] Bar
+//    | [<CompiledValue(null)>] Undefined // Error: Expected: undefined - Actual: undefined
+
 [<StringEnum>]
 #endif
 type Field = OldPassword | NewPassword | ConfirmPassword
@@ -829,6 +841,20 @@ let tests =
         let x = LowerAllOptions.ContentBox
         x |> unbox |> equal "contentbox"
 
+    testCase "StringEnum is overwritten by CompiledValue" <| fun () ->
+        RespectValues.ContentBox |> unbox |> equal "contentbox"
+        RespectValues.None |> unbox |> equal false
+        // When running fable-compiler-js we can't make a distinction between int and float at runtime
+        // See https://github.com/fable-compiler/Fable/pull/4144#issuecomment-3001681838
+        #if !NPM_PACKAGE_FABLE_COMPILER_JAVASCRIPT
+        RespectValues.Pi |> unbox |> equal 3.14159
+        #endif
+        RespectValues.AnswerToLife |> unbox |> equal 42
+        RespectValues.Foo |> unbox |> equal RespectValuesEnum.Foo
+
+    testCase "StringEnum CompiledName over CompiledValue" <| fun () ->
+        RespectValues.Bar |> unbox |> equal "Bar"
+
     // See https://github.com/fable-compiler/fable-import/issues/72
     testCase "Can use values and functions from global modules" <| fun () ->
         GlobalModule.add 3 4 |> equal 7