Improve error reporting for anonymous records declarations

src/Compiler/Checking/CheckExpressions.fs

@@ -4511,20 +4511,22 @@ and TcTupleType kindOpt (cenv: cenv) newOk checkConstraints occ env tpenv isStru
         else
             let argsR,tpenv = TcTypesAsTuple cenv newOk checkConstraints occ env tpenv args m
             TType_tuple(tupInfo, argsR), tpenv
+
+and CheckAnonRecdTypeDuplicateFields (elems: Ident array) =
+    elems |> Array.iteri (fun i (uc1: Ident) -> 
+        elems |> Array.iteri (fun j (uc2: Ident) -> 
+            if j > i && uc1.idText = uc2.idText then 
+               errorR(Error(FSComp.SR.tcAnonRecdTypeDuplicateFieldId(uc1.idText), uc1.idRange))))
 
 and TcAnonRecdType (cenv: cenv) newOk checkConstraints occ env tpenv isStruct args m =
     let tupInfo = mkTupInfo isStruct
+    let unsortedFieldIds = args |> List.map fst |> List.toArray
+    if unsortedFieldIds.Length > 1 then
+        CheckAnonRecdTypeDuplicateFields unsortedFieldIds
     let tup = args |> List.map (fun (_, t) -> SynTupleTypeSegment.Type t)
     let argsR,tpenv = TcTypesAsTuple cenv newOk checkConstraints occ env tpenv tup m
-    let unsortedFieldIds = args |> List.map fst |> List.toArray
     let anonInfo = AnonRecdTypeInfo.Create(cenv.thisCcu, tupInfo, unsortedFieldIds)
 
-    // Check for duplicate field IDs
-    unsortedFieldIds
-    |> Array.countBy (fun fieldId -> fieldId.idText)
-    |> Array.iter (fun (idText, count) ->
-        if count > 1 then error (Error (FSComp.SR.tcAnonRecdTypeDuplicateFieldId(idText), m)))
-
     // Sort into canonical order
     let sortedFieldTys, sortedCheckedArgTys = List.zip args argsR |> List.indexed |> List.sortBy (fun (i,_) -> unsortedFieldIds[i].idText) |> List.map snd |> List.unzip
 

tests/FSharp.Compiler.ComponentTests/Conformance/Types/RecordTypes/AnonymousRecords.fs

@@ -221,3 +221,85 @@ let x = {| abcd = {| ab = 4; cd = 1 |} |}
 """
         |> compile
         |> shouldSucceed
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record definition`` () =
+        Fsx """
+let x(f: {| A: int; A: int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 13, Line 2, Col 14, "The field 'A' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record definition 2`` () =
+        Fsx """
+let x(f: {| A: int; A: int; A:int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 13, Line 2, Col 14, "The field 'A' appears multiple times in this anonymous record type.")
+            (Error 3523, Line 2, Col 21, Line 2, Col 22, "The field 'A' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record declaration 3`` () =
+        Fsx """
+let f(x:{| A: int; B: int; A:string; B: int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 12, Line 2, Col 13, "The field 'A' appears multiple times in this anonymous record type.")
+            (Error 3523, Line 2, Col 20, Line 2, Col 21, "The field 'B' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record declaration 4`` () =
+        Fsx """
+let f(x:{| A: int; C: string; A: int; B: int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 12, Line 2, Col 13, "The field 'A' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record declaration 5`` () =
+        Fsx """
+let f(x:{| A: int; C: string; A: int; B: int; A: int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 12, Line 2, Col 13, "The field 'A' appears multiple times in this anonymous record type.")
+            (Error 3523, Line 2, Col 31, Line 2, Col 32, "The field 'A' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field with in double backticks appears multiple times in this anonymous record declaration`` () =
+        Fsx """
+let f(x:{| ``A``: int; B: int; A:string; B: int |}) = ()
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 12, Line 2, Col 17, "The field 'A' appears multiple times in this anonymous record type.")
+            (Error 3523, Line 2, Col 24, Line 2, Col 25, "The field 'B' appears multiple times in this anonymous record type.")
+        ]
+
+    [<Fact>]
+    let ``Anonymous Records field appears multiple times in this anonymous record declaration 6`` () =
+        Fsx """
+let foo: {| A: int; C: string; A: int; B: int; A: int |} = failwith "foo"
+        """
+        |> compile
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3523, Line 2, Col 13, Line 2, Col 14, "The field 'A' appears multiple times in this anonymous record type.")
+            (Error 3523, Line 2, Col 32, Line 2, Col 33, "The field 'A' appears multiple times in this anonymous record type.")
+        ]