[Rust] Add support for null strings (#4033)

src/Fable.Cli/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 * [Python] - Print root module and module function comments (by @alfonsogarciacaro)
+* [Rust] Add support for null strings (by @ncave)
 
 ## 5.0.0-alpha.9 - 2025-01-28
 

src/Fable.Compiler/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 * [Python] - Print root module and module function comments (by @alfonsogarciacaro)
+* [Rust] Add support for null strings (by @ncave)
 
 ## 5.0.0-alpha.9 - 2025-01-28
 

src/Fable.Transforms/Rust/Fable2Rust.fs

@@ -998,10 +998,11 @@ module TypeInfo =
         isNullable || isNotNullable && isReferenceType
 
     let transformGenericParamType com ctx name isMeasure constraints : Rust.Ty =
-        if isNullableReferenceType com ctx constraints then
-            // primitiveType name |> makeNullableTy com ctx
-            primitiveType name |> makeLrcPtrTy com ctx
-        elif isInferredGenericParam com ctx name isMeasure then
+        // if isNullableReferenceType com ctx constraints then
+        //     // primitiveType name |> makeNullableTy com ctx
+        //     primitiveType name |> makeLrcPtrTy com ctx
+        // elif
+        if isInferredGenericParam com ctx name isMeasure then
             mkInferTy () // mkNeverTy ()
         else
             primitiveType name
@@ -1734,7 +1735,7 @@ module Util =
         makeLibCall com ctx None "String" "fromString" [ value ]
 
     let makeNullCheck com ctx (value: Rust.Expr) =
-        makeLibCall com ctx None "Native" "isNull" [ value ]
+        makeLibCall com ctx None "Native" "is_null" [ value ]
 
     let makeNull com ctx (typ: Fable.Type) =
         let typ =
@@ -1743,7 +1744,7 @@ module Util =
             | t -> t
 
         let genArgsOpt = transformGenArgs com ctx [ typ ]
-        makeLibCall com ctx genArgsOpt "Native" "getNull" []
+        makeLibCall com ctx genArgsOpt "Native" "null" []
 
     let makeInit com ctx (typ: Fable.Type) =
         let genArgsOpt = transformGenArgs com ctx [ typ ]
@@ -2717,7 +2718,7 @@ module Util =
                 isByRefType com ident2.Type || ident2.IsMutable
                 ->
                 transformIdent com ctx None ident2 |> Some
-            | Fable.Value(Fable.Null _t, _) -> None // no init value, just a name declaration, to be initialized later
+            | Fable.Value(Fable.Null Fable.MetaType, _) -> None // special init value to skip initialization
             | Function(args, body, _name) -> transformLambda com ctx (Some ident.Name) args body |> Some
             | _ ->
                 transformLeaveContext com ctx None value
@@ -3876,6 +3877,11 @@ module Util =
             let genArgsOpt = mkConstraintArgs tys []
             mkTypeTraitGenericBound names genArgsOpt
 
+        let makeImportBound com ctx moduleName typeName =
+            let importName = getLibraryImportName com ctx moduleName typeName
+            let objectBound = mkTypeTraitGenericBound [ importName ] None
+            objectBound
+
         let makeRawBound id = makeGenBound [ rawIdent id ] []
 
         let makeOpBound op =
@@ -3914,7 +3920,7 @@ module Util =
                     else
                         []
                 | _ -> []
-            | Fable.Constraint.IsNullable -> []
+            | Fable.Constraint.IsNullable -> [ makeImportBound com ctx "Native" "NullableRef" ]
             | Fable.Constraint.IsNotNullable -> []
             | Fable.Constraint.IsValueType -> []
             | Fable.Constraint.IsReferenceType -> []
@@ -4513,9 +4519,10 @@ module Util =
                 let body =
                     (body, fieldIdents |> List.rev)
                     ||> List.fold (fun acc ident ->
-                        let nullOfT = Fable.Value(Fable.Null ident.Type, None)
+                        // use special init value to skip initialization (i.e. declaration only)
+                        let nullOfT = Fable.Value(Fable.Null Fable.MetaType, None)
                         Fable.Let(ident, nullOfT, acc)
-                    ) // will be transformed as declaration only
+                    )
 
                 body
             | e -> e

src/Fable.Transforms/Rust/Replacements.fs

@@ -465,7 +465,7 @@ let objectHash (com: ICompiler) ctx r (arg: Expr) =
 let referenceEquals (com: ICompiler) ctx r (left: Expr) (right: Expr) =
     match left, right with
     | Value(Null _, _), o
-    | o, Value(Null _, _) -> Helper.LibCall(com, "Native", "isNull", Boolean, [ o ], ?loc = r)
+    | o, Value(Null _, _) -> Helper.LibCall(com, "Native", "is_null", Boolean, [ o ], ?loc = r)
     | _ ->
         match left.Type with
         | Boolean
@@ -631,7 +631,7 @@ let rec getZero (com: ICompiler) (ctx: Context) (t: Type) =
     | Number(Decimal, _) -> Helper.LibValue(com, "Decimal", "Zero", t)
     | Number(kind, uom) -> NumberConstant(NumberValue.GetZero kind, uom) |> makeValue None
     | Char -> CharConstant '\u0000' |> makeValue None
-    | String -> makeStrConst "" // TODO: Use null for string?
+    | String -> Null t |> makeValue None
     | Array(typ, _) -> makeArray typ []
     | Builtin BclDateTime -> Helper.LibCall(com, "DateTime", "zero", t, [])
     | Builtin BclDateTimeOffset -> Helper.LibCall(com, "DateTimeOffset", "zero", t, [])
@@ -875,10 +875,12 @@ let makeRustFormatString interpolated (fmt: string) =
                     | _ -> ""
 
                 let argFmt =
-                    if g2 + g3 + g4 + g5 = "" then
+                    let formatting = g2 + g3 + g4 + g5
+
+                    if formatting = "" then
                         g1 + "{}"
                     else
-                        g1 + "{:" + g2 + g3 + g4 + g5 + "}"
+                        g1 + "{:" + formatting + "}"
 
                 argFmt
         )
@@ -1400,8 +1402,8 @@ let strings (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr opt
             Helper.LibCall(com, "String", methName, t, c :: args, ?loc = r) |> Some
         | _ -> None
     | "Insert", Some c, _ -> Helper.LibCall(com, "String", "insert", t, c :: args, ?loc = r) |> Some
-    | "IsNullOrEmpty", None, _ -> Helper.LibCall(com, "String", "isEmpty", t, args, ?loc = r) |> Some
-    | "IsNullOrWhiteSpace", None, _ -> Helper.LibCall(com, "String", "isWhitespace", t, args, ?loc = r) |> Some
+    | "IsNullOrEmpty", None, _ -> Helper.LibCall(com, "String", "isNullOrEmpty", t, args, ?loc = r) |> Some
+    | "IsNullOrWhiteSpace", None, _ -> Helper.LibCall(com, "String", "isNullOrWhitespace", t, args, ?loc = r) |> Some
     | "Join", None, _ ->
         let args =
             match args with
@@ -1992,8 +1994,10 @@ let optionModule isStruct (com: ICompiler) (ctx: Context) r (t: Type) (i: CallIn
     | "GetValue", [ c ] -> Get(c, OptionValue, t, r) |> Some
     | "IsSome", [ c ] -> Test(c, OptionTest true, r) |> Some
     | "IsNone", [ c ] -> Test(c, OptionTest false, r) |> Some
-    | "ToArray", [ arg ] -> Helper.LibCall(com, "Array", "ofOption", t, args, ?loc = r) |> Some
-    | "ToList", [ arg ] -> Helper.LibCall(com, "List", "ofOption", t, args, ?loc = r) |> Some
+    | "OfObj", [ arg ] -> Helper.LibCall(com, "Native", "ofObj", t, args, ?loc = r) |> Some
+    | "ToObj", [ arg ] -> Helper.LibCall(com, "Native", "toObj", t, args, ?loc = r) |> Some
+    // | "ToArray", [ arg ] -> Helper.LibCall(com, "Array", "ofOption", t, args, ?loc = r) |> Some
+    // | "ToList", [ arg ] -> Helper.LibCall(com, "List", "ofOption", t, args, ?loc = r) |> Some
     | meth, args ->
         Helper.LibCall(com, "Option", Naming.lowerFirst meth, t, args, i.SignatureArgTypes, ?loc = r)
         |> Some

src/fable-library-rust/src/Array.fs

@@ -893,11 +893,11 @@ let inline averageBy (projection: 'T -> 'U) (source: 'T[]) : 'U =
 
     LanguagePrimitives.DivideByInt total source.Length
 
-// Option.toArray redirects here to avoid dependency (see Replacements)
-let ofOption<'T> (opt: 'T option) : 'T[] =
-    match opt with
-    | Some x -> Array.singleton x
-    | None -> Array.empty
+// // Option.toArray redirects here to avoid dependency (see Replacements)
+// let ofOption<'T> (opt: 'T option) : 'T[] =
+//     match opt with
+//     | Some x -> Array.singleton x
+//     | None -> Array.empty
 
 // Redirected to List.toArray to avoid dependency (see Replacements)
 // let ofList (xs: 'T list): 'T[] = List.toArray

src/fable-library-rust/src/FuncType.rs

@@ -1,4 +1,4 @@
-use crate::Native_::{referenceEquals, referenceHash, Lrc};
+use crate::Native_::{referenceEquals, referenceHash, Lrc, NullableRef};
 
 macro_rules! func {
     ($f:ident $(,$i:ident)*) => {
@@ -12,7 +12,38 @@ macro_rules! func {
         #[derive(Clone)]
         pub enum $f<$($i, )*R> {
             Static(fn($($i, )*) -> R),
-            Shared(Option<Lrc<dyn Fn($($i, )*) -> R>>),
+            Shared(Lrc<dyn Fn($($i, )*) -> R>),
+            Null
+        }
+
+        #[cfg(not(feature = "enum_func"))]
+        impl<$($i, )*R> NullableRef for $f<$($i, )*R> {
+            #[inline]
+            fn null() -> Self {
+                $f(None)
+            }
+
+            #[inline]
+            fn is_null(&self) -> bool {
+                self.0.is_none()
+            }
+        }
+
+        #[cfg(feature = "enum_func")]
+        impl<$($i, )*R> NullableRef for $f<$($i, )*R> {
+            #[inline]
+            fn null() -> Self {
+                $f::Null
+            }
+
+            #[inline]
+            fn is_null(&self) -> bool {
+                match self {
+                    $f::Static(f) => false,
+                    $f::Shared(p) => false,
+                    $f::Null => true,
+                }
+            }
         }
 
         impl<$($i, )*R> core::fmt::Debug for $f<$($i, )*R> {
@@ -53,7 +84,7 @@ macro_rules! func {
         #[cfg(feature = "enum_func")]
         impl<$($i, )*R> Default for $f<$($i, )*R> {
             fn default() -> Self {
-                $f::Shared(None)
+                $f::Null
             }
         }
 
@@ -75,7 +106,8 @@ macro_rules! func {
             fn deref(&self) -> &Self::Target {
                 match self {
                     $f::Static(f) => f,
-                    $f::Shared(p) => p.as_ref().expect("Null reference exception.").as_ref(),
+                    $f::Shared(p) => p.as_ref(),
+                    $f::Null => panic!("Null reference exception."),
                 }
             }
         }
@@ -96,7 +128,7 @@ macro_rules! func {
                 $f::Static(f)
             }
             pub fn new<F: Fn($($i, )*) -> R + 'static>(f: F) -> Self {
-                $f::Shared(Some(Lrc::new(f) as Lrc<dyn Fn($($i, )*) -> R>))
+                $f::Shared(Lrc::new(f) as Lrc<dyn Fn($($i, )*) -> R>)
             }
         }
 

src/fable-library-rust/src/List.fs

@@ -92,11 +92,11 @@ let last (xs: 'T list) =
     | Some x -> x
     | None -> failwith SR.inputListWasEmpty
 
-// Option.toList redirects here to avoid dependency
-let ofOption<'T> (opt: 'T option) : 'T list =
-    match opt with
-    | Some x -> singleton x
-    | None -> empty ()
+// // Option.toList redirects here to avoid dependency
+// let ofOption<'T> (opt: 'T option) : 'T list =
+//     match opt with
+//     | Some x -> singleton x
+//     | None -> empty ()
 
 let ofSeq (xs: 'T seq) =
     let mutable root = None

src/fable-library-rust/src/LrcPtr.rs

@@ -1,7 +1,8 @@
-use crate::Native_::{Any, Lrc};
+use crate::Native_::{Any, Lrc, NullableRef};
 use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
 use core::ops::*;
+use core::panic::{RefUnwindSafe, UnwindSafe};
 
 // -----------------------------------------------------------
 // LrcPtr
@@ -11,31 +12,28 @@ use core::ops::*;
 #[repr(transparent)]
 pub struct LrcPtr<T: ?Sized>(Option<Lrc<T>>);
 
+impl<T: RefUnwindSafe + ?Sized> UnwindSafe for LrcPtr<T> {}
+impl<T: RefUnwindSafe + ?Sized> RefUnwindSafe for LrcPtr<T> {}
+
 impl<T> LrcPtr<T> {
     #[inline]
     pub fn new(value: T) -> Self {
         LrcPtr(Some(Lrc::new(value)))
     }
 }
 
-impl<T: ?Sized> LrcPtr<T> {
+impl<T: ?Sized> NullableRef for LrcPtr<T> {
     #[inline]
-    pub fn null() -> Self {
+    fn null() -> Self {
         LrcPtr(None)
     }
 
     #[inline]
-    pub fn is_null(&self) -> bool {
+    fn is_null(&self) -> bool {
         self.0.is_none()
     }
 }
 
-// impl<T: ?Sized> Default for LrcPtr<T> {
-//     fn default() -> Self {
-//         Self::null()
-//     }
-// }
-
 impl<T: ?Sized> From<Lrc<T>> for LrcPtr<T> {
     #[inline]
     fn from(value: Lrc<T>) -> Self {