Adjust FS-1075 : nullable interop - apply rule to all arguments, not just optional ones (#9316)

* adjust non-optional nullable interop

* adjust non-optional nullable interop

* fix error messages

* fix baseline

* fix baseline

Author: dsyme

src/fsharp/MethodCalls.fs

@@ -191,11 +191,13 @@ let AdjustCalledArgTypeForOptionals (g: TcGlobals) enforceNullableOptionalsKnown
             calledArgTy
     else
         match calledArg.OptArgInfo with 
-        | NotOptional ->
+        // CSharpMethod(x = arg), non-optional C#-style argument, may have type Nullable<ty>. 
+        | NotOptional when not (g.langVersion.SupportsFeature LanguageFeature.NullableOptionalInterop) ->
             calledArgTy
 
-        // CSharpMethod(x = arg), optional C#-style argument, may have type Nullable<ty>. 
         // The arg should have type ty. However for backwards compat, we also allow arg to have type Nullable<ty>
+        | NotOptional 
+        // CSharpMethod(x = arg), optional C#-style argument, may have type Nullable<ty>. 
         | CallerSide _ ->
             if isNullableTy g calledArgTy && g.langVersion.SupportsFeature LanguageFeature.NullableOptionalInterop then 
                 // If inference has worked out it's a nullable then use this
@@ -1148,21 +1150,40 @@ let GetDefaultExpressionForOptionalArg tcFieldInit g (calledArg: CalledArg) eCal
     let callerArg = CallerArg(calledArgTy, mMethExpr, false, expr)
     preBinder, { NamedArgIdOpt = None; CalledArg = calledArg; CallerArg = callerArg }
 
+let MakeNullableExprIfNeeded (infoReader: InfoReader) calledArgTy callerArgTy callerArgExpr m =
+    let g = infoReader.g
+    let amap = infoReader.amap
+    if isNullableTy g callerArgTy then 
+        callerArgExpr
+    else
+        let calledNonOptTy = destNullableTy g calledArgTy 
+        let minfo = GetIntrinsicConstructorInfosOfType infoReader m calledArgTy |> List.head
+        let callerArgExprCoerced = mkCoerceIfNeeded g calledNonOptTy callerArgTy callerArgExpr
+        MakeMethInfoCall amap m minfo [] [callerArgExprCoerced]
+
 // Adjust all the optional arguments, filling in values for defaults, 
 let AdjustCallerArgForOptional tcFieldInit eCallerMemberName (infoReader: InfoReader) (assignedArg: AssignedCalledArg<_>) =
     let g = infoReader.g
-    let amap = infoReader.amap
     let callerArg = assignedArg.CallerArg
     let (CallerArg(callerArgTy, m, isOptCallerArg, callerArgExpr)) = callerArg
     let calledArg = assignedArg.CalledArg
-    match calledArg.OptArgInfo with 
-    | NotOptional -> 
+    let calledArgTy = calledArg.CalledArgumentType
+    match calledArg.OptArgInfo with
+    | NotOptional when not (g.langVersion.SupportsFeature LanguageFeature.NullableOptionalInterop) ->
         if isOptCallerArg then errorR(Error(FSComp.SR.tcFormalArgumentIsNotOptional(), m))
         assignedArg
-    | _ -> 
+
+    | _ ->
+
         let callerArgExpr2 = 
             match calledArg.OptArgInfo with 
-            | NotOptional -> failwith "unreachable"
+            | NotOptional ->
+                //  T --> Nullable<T> widening at callsites
+                if isOptCallerArg then errorR(Error(FSComp.SR.tcFormalArgumentIsNotOptional(), m))
+                if isNullableTy g calledArgTy then 
+                    MakeNullableExprIfNeeded infoReader calledArgTy callerArgTy callerArgExpr m
+                else
+                    callerArgExpr
 
             | CallerSide dfltVal -> 
                 let calledArgTy = calledArg.CalledArgumentType
@@ -1184,15 +1205,9 @@ let AdjustCallerArgForOptional tcFieldInit eCallerMemberName (infoReader: InfoRe
                 else
                     if isNullableTy g calledArgTy  then 
                         // CSharpMethod(x=b) when 'x' has nullable type
-                        if isNullableTy g callerArgTy then 
-                            // CSharpMethod(x=b) when both 'x' and 'b' have nullable type --> CSharpMethod(x=b)
-                            callerArgExpr
-                        else
-                            // CSharpMethod(x=b) when 'x' has nullable type and 'b' does not --> CSharpMethod(x=Nullable(b))
-                            let calledNonOptTy = destNullableTy g calledArgTy 
-                            let minfo = GetIntrinsicConstructorInfosOfType infoReader m calledArgTy |> List.head
-                            let callerArgExprCoerced = mkCoerceIfNeeded g calledNonOptTy callerArgTy callerArgExpr
-                            MakeMethInfoCall amap m minfo [] [callerArgExprCoerced]
+                        // CSharpMethod(x=b) when both 'x' and 'b' have nullable type --> CSharpMethod(x=b)
+                        // CSharpMethod(x=b) when 'x' has nullable type and 'b' does not --> CSharpMethod(x=Nullable(b))
+                        MakeNullableExprIfNeeded infoReader calledArgTy callerArgTy callerArgExpr m
                     else 
                         // CSharpMethod(x=b) --> CSharpMethod(?x=b)
                         callerArgExpr
@@ -1203,7 +1218,6 @@ let AdjustCallerArgForOptional tcFieldInit eCallerMemberName (infoReader: InfoRe
                     callerArgExpr 
                 else                            
                     // CSharpMethod(x=b) when CSharpMethod(A) --> CSharpMethod(?x=Some(b :> A))
-                    let calledArgTy = assignedArg.CalledArg.CalledArgumentType
                     if isOptionTy g calledArgTy then 
                         let calledNonOptTy = destOptionTy g calledArgTy 
                         let callerArgExprCoerced = mkCoerceIfNeeded g calledNonOptTy callerArgTy callerArgExpr