Don't allow union case unnamed fields in <param> xmldoc

src/Compiler/Checking/CheckDeclarations.fs

@@ -531,7 +531,11 @@ module TcRecdUnionAndEnumDeclarations =
                     error(Error(FSComp.SR.tcReturnTypesForUnionMustBeSameAsType(), m))
                 rfields, recordTy
 
-        let names = rfields |> List.map (fun f -> f.DisplayNameCore)
+        let names = rfields
+                    |> Seq.filter (fun f -> not f.rfield_name_generated)
+                    |> Seq.map (fun f -> f.DisplayNameCore)
+                    |> Seq.toList
+
         let xmlDoc = xmldoc.ToXmlDoc(true, Some names)
         Construct.NewUnionCase id rfields recordTy attrs xmlDoc vis
 

src/FSharp.Core/prim-types.fs

@@ -3854,7 +3854,7 @@ namespace Microsoft.FSharp.Core
     [<DebuggerDisplay("{DebugDisplay,nq}")>]
     type ValueOption<'T> =
         | ValueNone : 'T voption
-        | ValueSome : 'T -> 'T voption
+        | ValueSome : Item: 'T -> 'T voption
 
         member x.Value = match x with ValueSome x -> x | ValueNone -> raise (new InvalidOperationException("ValueOption.Value"))
 

src/FSharp.Core/prim-types.fsi

@@ -2441,7 +2441,7 @@ namespace Microsoft.FSharp.Core
         /// <param name="Item">The input value.</param>
         ///
         /// <returns>An option representing the value.</returns>
-        | ValueSome: 'T -> 'T voption
+        | ValueSome: Item:'T -> 'T voption
 
         /// <summary>Get the value of a 'ValueSome' option. An InvalidOperationException is raised if the option is 'ValueNone'.</summary>
         member Value: 'T

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

@@ -206,4 +206,28 @@ module M =
          |> ignoreWarnings
          |> compile
          |> shouldSucceed
-         |> withDiagnostics [ ]
+         |> withDiagnostics [ ]
+
+    [<Fact>]
+    let ``Union field - unnamed 01`` () =
+        Fsx"""
+        type A =
+            /// <summary>A</summary>
+            /// <param name="Item">Item</param>
+            | A of int
+        """
+         |> withXmlCommentChecking
+         |> compile
+         |> withDiagnostics [ Warning 3390, Line 3, Col 13, Line 4, Col 48, "This XML comment is invalid: unknown parameter 'Item'" ]
+
+    [<Fact>]
+    let ``Union field - unnamed 02`` () =
+        Fsx"""
+        type A =
+            /// <summary>A</summary>
+            /// <param name="a">a</param>
+            | A of int * a: int
+        """
+         |> withXmlCommentChecking
+         |> compile
+         |> withDiagnostics [ ]