Bugfix :: Fix type definition metadata: duplicate methods, event flags (

#19341)
abonie · May 7, 2026 · Mar 24, 2026 · Mar 24, 2026 · Mar 24, 2026 · Mar 24, 2026
commit 0b8076968c6e6d567fe1bd1dd2977de9edd764cf
@@ -1,5 +1,8 @@
 ### Fixed
 
+* Fix DU case names matching IWSAM member names no longer cause duplicate property entries. (Issue [#14321](https://github.com/dotnet/fsharp/issues/14321), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))
+* Fix DefaultAugmentation(false) duplicate entry in method table. (Issue [#16565](https://github.com/dotnet/fsharp/issues/16565), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))
+* Fix abstract event accessors now have SpecialName flag. (Issue [#5834](https://github.com/dotnet/fsharp/issues/5834), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))
 * Fix CLIEvent properties to be correctly recognized as events: `IsEvent` returns `true` and `XmlDocSig` uses `E:` prefix instead of `P:`. ([Issue #10273](https://github.com/dotnet/fsharp/issues/10273), [PR #18584](https://github.com/dotnet/fsharp/pull/18584))
 * Fix extra sequence point at the end of match expressions. ([Issue #12052](https://github.com/dotnet/fsharp/issues/12052), [PR #19278](https://github.com/dotnet/fsharp/pull/19278))
 * Fix wrong sequence point range for `return`/`yield`/`return!`/`yield!` inside computation expressions. ([Issue #19248](https://github.com/dotnet/fsharp/issues/19248), [PR #19278](https://github.com/dotnet/fsharp/pull/19278))

@@ -13146,7 +13146,11 @@ let TcAndPublishValSpec (cenv: cenv, env, containerInfo: ContainerInfo, declKind
 
         let checkXmlDocs = cenv.diagnosticOptions.CheckXmlDocs
         let xmlDoc = xmlDoc.ToXmlDoc(checkXmlDocs, paramNames)
-        let vspec = MakeAndPublishVal cenv env (altActualParent, true, declKind, ValNotInRecScope, valscheme, attrs, xmlDoc, literalValue, false)
+        let isGeneratedEventVal =
+            CompileAsEvent g attrs
+            && (id.idText.StartsWithOrdinal("add_") || id.idText.StartsWithOrdinal("remove_"))
+
+        let vspec = MakeAndPublishVal cenv env (altActualParent, true, declKind, ValNotInRecScope, valscheme, attrs, xmlDoc, literalValue, isGeneratedEventVal)
 
         PublishArguments cenv env vspec synValSig allDeclaredTypars.Length
 

@@ -10903,6 +10903,13 @@ and GenAbstractBinding cenv eenv tref (vref: ValRef) =
         | SynMemberKind.Constructor
         | SynMemberKind.Member ->
             let mdef = mdef.With(customAttrs = mkILCustomAttrs ilAttrs)
+
+            let mdef =
+                if vref.Deref.val_flags.IsGeneratedEventVal then
+                    mdef.WithSpecialName
+                else
+                    mdef
+
             [ mdef ], [], []
         | SynMemberKind.PropertyGetSet -> error (Error(FSComp.SR.ilUnexpectedGetSetAnnotation (), m))
         | SynMemberKind.PropertySet
@@ -11927,6 +11934,17 @@ and GenTypeDef cenv mgbuf lazyInitInfo eenv m (tycon: Tycon) : ILTypeRef option
                     //
                     // Also discard the F#-compiler supplied implementation of the Empty, IsEmpty, Value and None properties.
 
+                    let nullaryCaseNames =
+                        if cuinfo.HasHelpers = AllHelpers || cuinfo.HasHelpers = NoHelpers then
+                            cuinfo.UnionCases
+                            |> Array.choose (fun alt -> if alt.IsNullary then Some alt.Name else None)
+                            |> Set.ofArray
+                        else
+                            Set.empty
+
+                    let isNullaryCaseClash name =
+                        not nullaryCaseNames.IsEmpty && nullaryCaseNames.Contains name
+
                     let tdefDiscards =
                         Some(
                             (fun (md: ILMethodDef) ->
@@ -11935,15 +11953,22 @@ and GenTypeDef cenv mgbuf lazyInitInfo eenv m (tycon: Tycon) : ILTypeRef option
                                 || (cuinfo.HasHelpers = SpecialFSharpOptionHelpers
                                     && (md.Name = "get_Value" || md.Name = "get_None" || md.Name = "Some"))
                                 || (cuinfo.HasHelpers = AllHelpers
-                                    && (md.Name.StartsWith("get_Is") && not (tdef2.Methods.FindByName(md.Name).IsEmpty)))),
+                                    && (md.Name.StartsWith("get_Is") && not (tdef2.Methods.FindByName(md.Name).IsEmpty)))
+                                || (md.Name.StartsWith("get_")
+                                    && md.Name.Length > 4
+                                    && isNullaryCaseClash (md.Name.Substring(4))
+                                    && not (tdef2.Methods.FindByName(md.Name).IsEmpty))),
 
                             (fun (pd: ILPropertyDef) ->
                                 (cuinfo.HasHelpers = SpecialFSharpListHelpers
                                  && (pd.Name = "Empty" || pd.Name = "IsEmpty"))
                                 || (cuinfo.HasHelpers = SpecialFSharpOptionHelpers
                                     && (pd.Name = "Value" || pd.Name = "None"))
                                 || (cuinfo.HasHelpers = AllHelpers
-                                    && (pd.Name.StartsWith("Is") && not (tdef2.Properties.LookupByName(pd.Name).IsEmpty))))
+                                    && (pd.Name.StartsWith("Is") && not (tdef2.Properties.LookupByName(pd.Name).IsEmpty)))
+                                || (isNullaryCaseClash pd.Name
+                                    && (not (tdef2.Properties.LookupByName(pd.Name).IsEmpty)
+                                        || not (tdef2.Methods.FindByName("get_" + pd.Name).IsEmpty))))
                         )
 
                     tdef2, tdefDiscards

@@ -0,0 +1,289 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace EmittedIL
+
+open Xunit
+open FSharp.Test
+open FSharp.Test.Compiler
+
+module CodeGenRegressions_TypeDefs =
+
+    // https://github.com/dotnet/fsharp/issues/16565
+    [<Fact>]
+    let ``Issue_16565_DefaultAugmentationFalseDuplicateEntry`` () =
+        let source = """
+module Test
+
+open System
+
+[<DefaultAugmentation(false)>]
+type Option<'T> =
+    | Some of Value: 'T
+    | None
+
+    member x.Value =
+        match x with
+        | Some x -> x
+        | None -> raise (new InvalidOperationException("Option.Value"))
+
+    static member None : Option<'T> = None
+
+and 'T option = Option<'T>
+
+let v = Option.Some 42
+printfn "Value: %d" v.Value
+let n = Option<int>.None
+printfn "None created successfully"
+"""
+        FSharp source
+        |> asExe
+        |> compile
+        |> shouldSucceed
+        |> run
+        |> shouldSucceed
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/14321
+    [<Fact>]
+    let ``Issue_14321_DuAndIWSAMNames`` () =
+        let source = """
+module Test
+
+#nowarn "3535"  // IWSAM warning
+
+type EngineError<'e> =
+    static abstract Overheated : 'e
+    static abstract LowOil : 'e
+
+type CarError =
+    | Overheated
+    | LowOil
+    | DeviceNotPaired
+
+    interface EngineError<CarError> with
+        static member Overheated = Overheated
+        static member LowOil = LowOil
+"""
+        FSharp source
+        |> asLibrary
+        |> compile
+        |> shouldSucceed
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/14321
+    // Runtime test: type must load without "duplicate entry in method table"
+    [<Fact>]
+    let ``Issue_14321_DuAndIWSAMNames_Runtime`` () =
+        let source = """
+module Test
+
+#nowarn "3535"
+
+type EngineError<'e> =
+    static abstract Overheated : 'e
+    static abstract LowOil : 'e
+
+type CarError =
+    | Overheated
+    | LowOil
+    | DeviceNotPaired
+
+    interface EngineError<CarError> with
+        static member Overheated = Overheated
+        static member LowOil = LowOil
+
+[<EntryPoint>]
+let main _ =
+    let err = CarError.Overheated
+    match err with
+    | Overheated -> printfn "Got Overheated"
+    | LowOil -> printfn "Got LowOil"
+    | DeviceNotPaired -> printfn "Got DeviceNotPaired"
+    0
+"""
+        FSharp source
+        |> asExe
+        |> compile
+        |> shouldSucceed
+        |> run
+        |> shouldSucceed
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/5834
+    [<Fact>]
+    let ``Issue_5834_EventSpecialname`` () =
+        let source = """
+module Test
+
+open System
+open System.Reflection
+
+type IAbstract1 =
+    [<CLIEvent>]
+    abstract member Event : IEvent<EventHandler, EventArgs>
+
+type IAbstract2 =
+    [<CLIEvent>]
+    abstract member Event : IDelegateEvent<EventHandler>
+
+[<AbstractClass>]
+type Abstract3() =
+    [<CLIEvent>]
+    abstract member Event : IDelegateEvent<EventHandler>
+
+type Concrete1() =
+    let event = new Event<EventHandler, EventArgs>()
+    [<CLIEvent>]
+    member this.Event = event.Publish
+
+type Concrete2() =
+    [<CLIEvent>]
+    member this.Event = { new IDelegateEvent<EventHandler> with
+                              member this.AddHandler _ = ()
+                              member this.RemoveHandler _ = () }
+
+type ConcreteWithObsolete() =
+    let evt = new Event<EventHandler, EventArgs>()
+    [<Obsolete("deprecated")>]
+    [<CLIEvent>]
+    member this.MyEvent = evt.Publish
+
+[<EntryPoint>]
+let main _ =
+    let mutable failures = 0
+    let check (t: Type) =
+        t.GetMethods(BindingFlags.Public ||| BindingFlags.Instance ||| BindingFlags.DeclaredOnly)
+        |> Array.filter (fun m -> m.Name.Contains("Event"))
+        |> Array.iter (fun m ->
+            if not m.IsSpecialName then
+                printfn "FAIL: %s.%s missing specialname" t.Name m.Name
+                failures <- failures + 1)
+
+    check typeof<IAbstract1>
+    check typeof<IAbstract2>
+    check typeof<Abstract3>
+    check typeof<Concrete1>
+    check typeof<Concrete2>
+    check typeof<ConcreteWithObsolete>
+
+    if failures > 0 then
+        failwithf "BUG: %d event accessors missing specialname" failures
+    printfn "SUCCESS: All event accessors have specialname"
+    0
+"""
+        FSharp source
+        |> asExe
+        |> compile
+        |> shouldSucceed
+        |> run
+        |> shouldSucceed
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/5834
+    // IL verification: abstract event accessors must have specialname flag
+    [<Fact>]
+    let ``Issue_5834_EventSpecialname_IL`` () =
+        let source = """
+module Test
+
+open System
+
+type IAbstract1 =
+    [<CLIEvent>]
+    abstract member Event : IEvent<EventHandler, EventArgs>
+
+[<AbstractClass>]
+type Abstract2() =
+    [<CLIEvent>]
+    abstract member Event : IDelegateEvent<EventHandler>
+"""
+        FSharp source
+        |> asLibrary
+        |> compile
+        |> shouldSucceed
+        |> verifyIL [
+            // Interface abstract event accessors have specialname
+            """.method public hidebysig specialname abstract virtual instance void  add_Event(class [runtime]System.EventHandler A_1) cil managed"""
+
+            """.method public hidebysig specialname abstract virtual instance void  remove_Event(class [runtime]System.EventHandler A_1) cil managed"""
+
+            // IAbstract1 event references its accessors
+            """.addon instance void Test/IAbstract1::add_Event(class [runtime]System.EventHandler)"""
+            """.removeon instance void Test/IAbstract1::remove_Event(class [runtime]System.EventHandler)"""
+
+            // Abstract2 event also references its specialname accessors
+            """.addon instance void Test/Abstract2::add_Event(class [runtime]System.EventHandler)"""
+            """.removeon instance void Test/Abstract2::remove_Event(class [runtime]System.EventHandler)"""
+        ]
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/14321
+    // IL verification: DU case properties and IWSAM implementations coexist without duplicates
+    [<Fact>]
+    let ``Issue_14321_DuAndIWSAMNames_IL`` () =
+        let source = """
+module Test
+
+#nowarn "3535"
+
+type EngineError<'e> =
+    static abstract Overheated : 'e
+    static abstract LowOil : 'e
+
+type CarError =
+    | Overheated
+    | LowOil
+    | DeviceNotPaired
+
+    interface EngineError<CarError> with
+        static member Overheated = Overheated
+        static member LowOil = LowOil
+"""
+        FSharp source
+        |> asLibrary
+        |> compile
+        |> shouldSucceed
+        |> verifyIL [
+            // DU case property getter exists on CarError
+            """.method public static class Test/CarError get_Overheated() cil managed"""
+
+            // Explicit IWSAM implementation uses mangled name
+            """.method public hidebysig specialname static class Test/CarError  'Test.EngineError<Test.CarError>.get_Overheated'() cil managed"""
+
+            // Explicit IWSAM for LowOil also present
+            """.method public hidebysig specialname static class Test/CarError  'Test.EngineError<Test.CarError>.get_LowOil'() cil managed"""
+        ]
+        |> ignore
+
+    // https://github.com/dotnet/fsharp/issues/16565
+    // IL verification: DefaultAugmentation(false) produces no duplicate method table entries
+    [<Fact>]
+    let ``Issue_16565_DefaultAugmentationFalseDuplicateEntry_IL`` () =
+        let source = """
+module Test
+
+[<DefaultAugmentation(false)>]
+type MyOption<'T> =
+    | Some of Value: 'T
+    | None
+
+    member x.Value =
+        match x with
+        | Some x -> x
+        | None -> failwith "no value"
+
+    static member None : MyOption<'T> = None
+"""
+        FSharp source
+        |> asLibrary
+        |> compile
+        |> shouldSucceed
+        |> verifyIL [
+            // The user-defined get_Value method exists on the main type with specialname
+            """.method public hidebysig specialname instance !T  get_Value() cil managed"""
+
+            // The static get_None method exists
+            """.method public static class Test/MyOption`1<!T> get_None() cil managed"""
+        ]
+        |> ignore
+
@@ -280,6 +280,7 @@
     <Compile Include="EmittedIL\Nullness\NullnessMetadata.fs" />
     <Compile Include="EmittedIL\FixedBindings\FixedBindings.fs" />
     <Compile Include="EmittedIL\CodeGenRegressions\CodeGenRegressions_Observations.fs" />
+    <Compile Include="EmittedIL\CodeGenRegressions\CodeGenRegressions_TypeDefs.fs" />
     <Compile Include="EmittedIL\CodeGenRegressions\CodeGenRegressions_Signatures.fs" />
     <Compile Include="EmittedIL\CodeGenRegressions\CodeGenRegressions_Closures.fs" />
     <Compile Include="ErrorMessages\TypedInterpolatedStringsTests.fs" />