Implement walking of Attribute super types to check AttributeUsage

src/fsharp/TypedTreeOps.fs

@@ -3013,6 +3013,11 @@ let superOfTycon (g: TcGlobals) (tycon: Tycon) =
     | None -> g.obj_ty 
     | Some ty -> ty 
 
+/// walk a TyconRef's inheritance tree, yielding any parent types as an array
+let supersOfTyconRef (tcref: TyconRef) =
+    Array.unfold (fun (tcref: TyconRef) -> match tcref.TypeContents.tcaug_super with Some (TType_app(sup, _)) -> Some(sup, sup) | _ -> None) tcref
+
+
 //----------------------------------------------------------------------------
 // Detect attributes
 //----------------------------------------------------------------------------
@@ -3119,12 +3124,16 @@ let TryFindTyconRefBoolAttribute g m attribSpec tcref =
                    | ([ Some ((:? bool as v) : obj) ], _) -> Some v 
                    | _ -> None)
 
+/// Try to find the resolved attributeusage for an type by walking its inheritance tree and picking the correct attribute usage value
 let TryFindAttributeUsageAttribute g m tcref =
-    TryBindTyconRefAttribute g m g.attrib_AttributeUsageAttribute tcref 
+    [| yield tcref
+       yield! supersOfTyconRef tcref |]
+    |> Array.tryPick (fun tcref ->
+        TryBindTyconRefAttribute g m g.attrib_AttributeUsageAttribute tcref
                 (fun (_, named) -> named |> List.tryPick (function ("AllowMultiple", _, _, ILAttribElem.Bool res) -> Some res | _ -> None))
                 (fun (Attrib(_, _, _, named, _, _, _)) -> named |> List.tryPick (function AttribNamedArg("AllowMultiple", _, _, AttribBoolArg res ) -> Some res | _ -> None))
                 (fun (_, named) -> named |> List.tryPick (function ("AllowMultiple", Some ((:? bool as res) : obj)) -> Some res | _ -> None))
-
+    )
 
 /// Try to find a specific attribute on a type definition, where the attribute accepts a string argument.
 ///

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -43,6 +43,7 @@
     <Compile Include="ErrorMessages\WrongSyntaxInForLoop.fs" />
     <Compile Include="ErrorMessages\ConfusingTypeName.fs" />
     <Compile Include="Language\RegressionTests.fs" />
+    <Compile Include="Language\AttributeCheckingTests.fs" />
     <Compile Include="Language\XmlComments.fs" />
     <Compile Include="Language\CompilerDirectiveTests.fs" />
     <Compile Include="Language\CodeQuotationTests.fs" />

tests/FSharp.Compiler.ComponentTests/Language/AttributeCheckingTests.fs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace FSharp.Compiler.ComponentTests.AttributeChecking
+
+open Xunit
+open FSharp.Test.Utilities.Compiler
+
+module AttributeCheckingTests =
+
+    [<Fact>]
+    let ``attributes check inherited AllowMultiple`` () =
+        Fsx """
+open System
+
+[<AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)>]
+type HttpMethodAttribute() = inherit Attribute()
+type HttpGetAttribute() = inherit HttpMethodAttribute()
+
+[<HttpGet; HttpGet>] // this shouldn't error like 
+[<HttpMethod; HttpMethod>] // this doesn't
+type C() =
+    member _.M() = ()
+        """
+         |> ignoreWarnings
+         |> compile
+         |> shouldSucceed
+