Fix missing TailCall warning in Sequential in use scope, #17897 (#17927)

docs/release-notes/.FSharp.Compiler.Service/9.0.200.md

@@ -1,5 +1,6 @@
 ### Fixed
 
+* Fix missing TailCall warning in Sequential in use scope ([PR #17927](https://github.com/dotnet/fsharp/pull/17927))
 * Fix false negatives for passing null to "obj" arguments. Only "obj | null" can now subsume any type ([PR #17757](https://github.com/dotnet/fsharp/pull/17757))
 * Fix internal error when calling 'AddSingleton' and other overloads only differing in generic arity ([PR #17804](https://github.com/dotnet/fsharp/pull/17804))
 * Fix extension methods support for non-reference system assemblies ([PR #17799](https://github.com/dotnet/fsharp/pull/17799))

src/Compiler/Checking/TailCallChecks.fs

@@ -792,6 +792,7 @@ let CheckModuleBinding cenv (isRec: bool) (TBind _ as bind) =
                     // warn for recursive calls in TryWith/TryFinally operations
                     exprs |> Seq.iter (checkTailCall true)
                 | Expr.Op(args = exprs) -> exprs |> Seq.iter (checkTailCall insideSubBindingOrTry)
+                | Expr.Sequential(expr2 = expr2) -> checkTailCall insideSubBindingOrTry expr2
                 | _ -> ()
 
             checkTailCall false bodyExpr

tests/FSharp.Compiler.ComponentTests/ErrorMessages/TailCallAttribute.fs

@@ -473,6 +473,34 @@ namespace N
                 "The member or function 'f' has the 'TailCallAttribute' attribute, but is not being used in a tail recursive way." }
         ]
 
+    [<FSharp.Test.FactForNETCOREAPP>]
+    let ``Warn for rec call in Sequential in use scope`` () =
+        """
+namespace N
+
+    module M =
+
+        [<TailCall>]
+        let rec f () =
+            let path = System.IO.Path.GetTempFileName()
+            use file = System.IO.File.Open(path, System.IO.FileMode.Open)
+            printfn "Hi!"
+            f ()
+        """
+        |> FSharp
+        |> withLangVersion80
+        |> compile
+        |> shouldFail
+        |> withResults [
+            { Error = Warning 3569
+              Range = { StartLine = 11
+                        StartColumn = 13
+                        EndLine = 11
+                        EndColumn = 14 }
+              Message =
+                "The member or function 'f' has the 'TailCallAttribute' attribute, but is not being used in a tail recursive way." }
+        ]
+
     [<FSharp.Test.FactForNETCOREAPP>]
     let ``Warn for invalid tailcalls in async expression`` () =
         """