Mixing named arguments + callback style and getter should not compile

src/Compiler/Checking/CheckDeclarations.fs

@@ -4313,7 +4313,19 @@ module TcDeclarations =
             for slot in ds do
                 if isAbstractSlot slot then
                     match slot with
-                    | SynMemberDefn.AbstractSlot (slotSig = synVal; range = m) ->
+                    | SynMemberDefn.AbstractSlot (slotSig = synVal; flags = flags; range = m) as slot ->
+                        let (SynValSig(ident = SynIdent(id, _); synType = synType)) = synVal
+                        let hasNamedArgs =
+                            match synType with
+                            | SynType.Fun(argType= SynType.Tuple(path = pathSegments); returnType = _) ->
+                                pathSegments
+                                |> List.exists (function SynTupleTypeSegment.Type(SynType.SignatureParameter(id = Some id)) -> true | _ -> false)
+                            | _ -> false
+
+                        let isGetterSetter = flags.MemberKind = SynMemberKind.PropertyGetSet || flags.MemberKind = SynMemberKind.PropertySet || flags.MemberKind = SynMemberKind.PropertyGet
+                        // Indexed properties uses "Item"y member name and are allowed with get and set
+                        if id.idText <> "Item" && hasNamedArgs && isGetterSetter then
+                            errorR(Error(FSComp.SR.tcAbstractPropertyCannotHaveNamedArgumentsWithGetSet(), m))
                         CheckDuplicatesArgNames synVal m
                     | _ -> ()
 

src/Compiler/FSComp.txt

@@ -1788,3 +1788,4 @@ featureUseTypeSubsumptionCache,"Use type conversion cache during compilation"
 featureDontWarnOnUppercaseIdentifiersInBindingPatterns,"Don't warn on uppercase identifiers in binding patterns"
 3873,chkDeprecatePlacesWhereSeqCanBeOmitted,"This construct is deprecated. Sequence expressions should be of the form 'seq {{ ... }}'"
 featureDeprecatePlacesWhereSeqCanBeOmitted,"Deprecate places where 'seq' can be omitted"
+3874,tcAbstractPropertyCannotHaveNamedArgumentsWithGetSet,"Abstract properties cannot have named arguments with get and set accessors."

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/MemberDefinitions/MethodsAndProperties/MethodsAndProperties.fs

@@ -613,6 +613,23 @@ type MyIndexerClass() =
         |> typecheck
         |> shouldFail
         |> withSingleDiagnostic (Warning 3581, Line 3, Col 14, Line 3, Col 22, "An indexed property's getter and setter must have the same type. Property 'Indexer1' has getter of type 'string' but setter of type 'float'.")
+
+    [<Fact>]
+    let ``Mixing named arguments + callback style and getter should not compile``() =
+        Fsx """
+type MyFunc = string * string option -> unit
+
+type LabeledProperty = 
+    abstract member alert: title:string * message:string option -> unit with get,set
+    abstract member alert2: string * string option -> unit with get,set
+    abstract member alert3: (string * string option -> unit) with get,set
+    abstract member alert4: MyFunc with get,set
+"""
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3874, Line 5, Col 5, Line 5, Col 85, "Abstract properties cannot have named arguments with get and set accessors.")
+        ]
 
     [<Fact>]
     let ``Indexed2PropertiesSameType_fs preview``() =