fix tuple warnings (#4389)

* fix tuple warnings

* fix tuple warnings

* fix tuple warnings

* fix tuple warnings

src/fsharp/TypeChecker.fs

@@ -174,7 +174,7 @@ let MethInfoChecks g amap isInstance tyargsOpt objArgs ad m (minfo:MethInfo)  =
     if not (IsTypeAndMethInfoAccessible amap m adOriginal ad minfo) then 
       error (Error (FSComp.SR.tcMethodNotAccessible(minfo.LogicalName), m))
 
-    if isAnyTupleTy g minfo.ApparentEnclosingType then 
+    if isAnyTupleTy g minfo.ApparentEnclosingType && not minfo.IsExtensionMember && (minfo.LogicalName.StartsWith "get_Item" || minfo.LogicalName.StartsWith "get_Rest") then
       warning (Error (FSComp.SR.tcTupleMemberNotNormallyUsed(), m))
 
     CheckMethInfoAttributes g m tyargsOpt minfo |> CommitOperationResult

tests/fsharp/typecheck/sigs/neg101.fs

 
 module M
-
+open System
 type MyRec = { Foo: string }
 
 let x: int = 1
@@ -47,4 +47,16 @@ let x1 =
      (1,2,3,4,5,6,7,8).Item7 ]
 
 let x2 = (1,2,3,4,5,6,7,8).Rest // gives a warning
-let x3 = (1,2).Rest // gives an actual error
\ No newline at end of file
+let x3 = (1,2).Rest // gives an actual error
+let x4 = (struct (1,2)).ToTuple() // no error or warning
+
+open System.Runtime.CompilerServices
+
+[<Extension>]
+type TupleEx() =
+    [<Extension>]
+    static member inline Do((x,y): (int*string)) = ()
+    
+let x = 1, "2"
+
+x.Do() // no warning