more tests

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

@@ -529,4 +529,78 @@ let f3 =
         |> shouldFail
         |> withDiagnostics [
             (Error 708, Line 5, Col 13, Line 5, Col 19, "This control construct may only be used if the computation expression builder defines a 'YieldFrom' method")
+        ]
+
+
+    [<Fact>]
+    let ``This control construct may only be used if the computation expression builder defines a 'Return' method`` () =
+        Fsx """
+module Result =
+    let zip x1 x2 =
+        match x1,x2 with
+        | Ok x1res, Ok x2res -> Ok (x1res, x2res)
+        | Error e, _ -> Error e
+        | _, Error e -> Error e
+
+type ResultBuilder() =
+    member _.MergeSources(t1: Result<'T,'U>, t2: Result<'T1,'U>) = Result.zip t1 t2
+    member _.BindReturn(x: Result<'T,'U>, f) = Result.map f x
+    member _.Delay(f) = f()
+    
+    member _.TryWith(r: Result<'T,'U>, f) =
+        match r with
+        | Ok x -> Ok x
+        | Error e -> f e
+
+let result = ResultBuilder()
+
+let run r2 r3 =
+    result {
+        match r2 with
+        | Ok x -> return x
+        | Error e -> return e
+    }
+        """
+        |> ignoreWarnings
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 708, Line 24, Col 19, Line 24, Col 25, "This control construct may only be used if the computation expression builder defines a 'Return' method")
+        ]
+
+
+    [<Fact>]
+    let ``This control construct may only be used if the computation expression builder defines a 'ReturnFrom' method`` () =
+        Fsx """
+module Result =
+    let zip x1 x2 =
+        match x1,x2 with
+        | Ok x1res, Ok x2res -> Ok (x1res, x2res)
+        | Error e, _ -> Error e
+        | _, Error e -> Error e
+
+type ResultBuilder() =
+    member _.MergeSources(t1: Result<'T,'U>, t2: Result<'T1,'U>) = Result.zip t1 t2
+    member _.BindReturn(x: Result<'T,'U>, f) = Result.map f x
+    member _.Delay(f) = f()
+    
+    member _.TryWith(r: Result<'T,'U>, f) =
+        match r with
+        | Ok x -> Ok x
+        | Error e -> f e
+
+let result = ResultBuilder()
+
+let run r2 r3 =
+    result {
+        match r2 with
+        | Ok x -> return! x
+        | Error e -> return e
+    }
+        """
+        |> ignoreWarnings
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 708, Line 24, Col 19, Line 24, Col 26, "This control construct may only be used if the computation expression builder defines a 'ReturnFrom' method")
         ]

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

@@ -454,4 +454,17 @@ let f2 = yield! [ 3; 4 ]
     |> withDiagnostics [
         (Error 747, Line 2, Col 10, Line 2, Col 15, "This construct may only be used within list, array and sequence expressions, e.g. expressions of the form 'seq { ... }', '[ ... ]' or '[| ... |]'. These use the syntax 'for ... in ... do ... yield...' to generate elements");
         (Error 747, Line 3, Col 10, Line 3, Col 16, "This construct may only be used within list, array and sequence expressions, e.g. expressions of the form 'seq { ... }', '[ ... ]' or '[| ... |]'. These use the syntax 'for ... in ... do ... yield...' to generate elements")
+    ]
+
+[<Fact>]
+let ``return may only be used within list, array, and sequence expressions``() =
+    Fsx """
+let f1 = return [ 3; 4 ] 
+let f2 = return! [ 3; 4 ] 
+    """
+    |> typecheck
+    |> shouldFail
+    |> withDiagnostics [
+        (Error 748, Line 2, Col 10, Line 2, Col 16, "This construct may only be used within computation expressions. To return a value from an ordinary function simply write the expression without 'return'.");
+        (Error 748, Line 3, Col 10, Line 3, Col 17, "This construct may only be used within computation expressions. To return a value from an ordinary function simply write the expression without 'return'.")
     ]