Prevent assignment to literal ILFields (#9797)

* Prevent assignment to literal ILFields

* revert old mechanism

* add new error message, use it, and provide localizations

* add error message for literal and non-literal assignment

* first stab at tests

* flip directory separator in test project file

* fix namespace on file to allow for it to be picked up

* Update src/fsharp/TypeChecker.fs

Co-authored-by: Phillip Carter <pcarter@fastmail.com>

* Update tests/FSharp.Compiler.ComponentTests/Interop/SimpleInteropTests.fs

Co-authored-by: Phillip Carter <pcarter@fastmail.com>

* Update tests/FSharp.Compiler.ComponentTests/Interop/SimpleInteropTests.fs

Co-authored-by: Phillip Carter <pcarter@fastmail.com>

Co-authored-by: Phillip Carter <pcarter@fastmail.com>

Author: baronfel

src/fsharp/FSComp.txt

@@ -1512,8 +1512,10 @@ featureFixedIndexSlice3d4d,"fixed-index slice 3d/4d"
 featureAndBang,"applicative computation expressions"
 featureNullableOptionalInterop,"nullable optional interop"
 featureDefaultInterfaceMemberConsumption,"default interface member consumption"
+featureWitnessPassing,"witness passing for trait constraints in F# quotations"
+3353,fsiInvalidDirective,"Invalid directive '#%s %s'"
 3360,typrelInterfaceWithConcreteAndVariable,"'%s' cannot implement the interface '%s' with the two instantiations '%s' and '%s' because they may unify."
 3361,typrelInterfaceWithConcreteAndVariableObjectExpression,"You cannot implement the interface '%s' with the two instantiations '%s' and '%s' because they may unify."
 featureInterfacesWithMultipleGenericInstantiation,"interfaces with multiple generic instantiation"
-featureWitnessPassing,"witness passing for trait constraints in F# quotations"
-3353,fsiInvalidDirective,"Invalid directive '#%s %s'"
+3362,tcLiteralFieldAssignmentWithArg,"Cannot assign '%s' to a value marked literal"
+3363,tcLiteralFieldAssignmentNoArg,"Cannot assign a value to another value marked literal"

src/fsharp/TypeChecker.fs

@@ -3137,6 +3137,18 @@ let BuildILFieldGet g amap m objExpr (finfo: ILFieldInfo) =
     // Add an I_nop if this is an initonly field to make sure we never recognize it as an lvalue. See mkExprAddrOfExpr. 
     wrap (mkAsmExpr (([ mkNormalLdfld fspec ] @ (if finfo.IsInitOnly then [ AI_nop ] else [])), tinst, [objExpr], [fieldType], m)) 
 
+/// Checks that setting a field value does not set a literal or initonly field
+let private CheckFieldLiteralArg (finfo: ILFieldInfo) argExpr m =
+    finfo.LiteralValue |> Option.iter (fun _ ->
+        match argExpr with
+        | Expr.Const (v, _, _) ->
+            let literalValue = string v
+            error (Error(FSComp.SR.tcLiteralFieldAssignmentWithArg literalValue, m))
+        | _ ->
+            error (Error(FSComp.SR.tcLiteralFieldAssignmentNoArg(), m))
+    )
+    if finfo.IsInitOnly then error (Error (FSComp.SR.tcFieldIsReadonly(), m))
+
 let BuildILFieldSet g m objExpr (finfo: ILFieldInfo) argExpr = 
     let fref = finfo.ILFieldRef
     let isValueType = finfo.IsValueType
@@ -3146,7 +3158,7 @@ let BuildILFieldSet g m objExpr (finfo: ILFieldInfo) argExpr =
       // This ensures we always get the type instantiation right when doing this from 
       // polymorphic code, after inlining etc. *
     let fspec = mkILFieldSpec(fref, mkILNamedTy valu fref.DeclaringTypeRef [])
-    if finfo.IsInitOnly then error (Error (FSComp.SR.tcFieldIsReadonly(), m))
+    CheckFieldLiteralArg finfo argExpr m
     let wrap, objExpr, _readonly, _writeonly = mkExprAddrOfExpr g isValueType false DefinitelyMutates objExpr None m 
     wrap (mkAsmExpr ([ mkNormalStfld fspec ], tinst, [objExpr; argExpr], [], m)) 
 
@@ -3159,9 +3171,9 @@ let BuildILStaticFieldSet m (finfo: ILFieldInfo) argExpr =
       // This ensures we always get the type instantiation right when doing this from 
       // polymorphic code, after inlining etc. 
     let fspec = mkILFieldSpec(fref, mkILNamedTy valu fref.DeclaringTypeRef [])
-    if finfo.IsInitOnly then error (Error (FSComp.SR.tcFieldIsReadonly(), m))
+    CheckFieldLiteralArg finfo argExpr m
     mkAsmExpr ([ mkNormalStsfld fspec ], tinst, [argExpr], [], m)
-    
+
 let BuildRecdFieldSet g m objExpr (rfinfo: RecdFieldInfo) argExpr = 
     let tgtTy = rfinfo.DeclaringType
     let valu = isStructTy g tgtTy