Split ToGodot/FromGodot -> internal Engine* traits

Allows to treat user-defined #[func] conversions separately
from engine-provided APIs (class methods, enums, ...).

Removes #[func] support for u64.

Author: Bromeon

godot-codegen/src/generator/enums.rs

@@ -127,8 +127,10 @@ pub fn make_enum_definition_with(
 
             impl crate::meta::FromGodot for #name {
                 fn try_from_godot(via: Self::Via) -> std::result::Result<Self, crate::meta::error::ConvertError> {
+                    // Pass i32/u64 enum/bitfield as i64 on the FFI layer. Only necessary for bitfields (u64).
+                    // Bitfields are cast to i64 for FFI, then reinterpreted in C++ as uint64_t.
                     <Self as #engine_trait>::try_from_ord(via)
-                        .ok_or_else(|| crate::meta::error::FromGodotError::InvalidEnum.into_error(via))
+                        .ok_or_else(|| crate::meta::error::FromGodotError::InvalidEnum.into_error(via as i64))
                 }
             }
         }

godot-core/src/builtin/variant/mod.rs

@@ -16,8 +16,8 @@ use crate::builtin::{
 use crate::classes;
 use crate::meta::error::{ConvertError, FromVariantError};
 use crate::meta::{
-    arg_into_ref, ffi_variant_type, ArrayElement, AsArg, ExtVariantType, FromGodot, GodotType,
-    ToGodot,
+    arg_into_ref, ffi_variant_type, ArrayElement, AsArg, EngineFromGodot, ExtVariantType,
+    FromGodot, GodotType, ToGodot,
 };
 
 mod impls;
@@ -118,14 +118,18 @@ impl Variant {
         try_from_variant_relaxed(self)
     }
 
+    pub(crate) fn engine_try_to_relaxed<T: EngineFromGodot>(&self) -> Result<T, ConvertError> {
+        try_from_variant_relaxed(self)
+    }
+
     /// Helper function for relaxed variant conversion with panic on failure.
     /// Similar to [`to()`](Self::to) but uses relaxed conversion rules.
     pub(crate) fn to_relaxed_or_panic<T, F>(&self, context: F) -> T
     where
-        T: FromGodot,
+        T: EngineFromGodot,
         F: FnOnce() -> String,
     {
-        self.try_to_relaxed::<T>()
+        self.engine_try_to_relaxed::<T>()
             .unwrap_or_else(|err| panic!("{}: {err}", context()))
     }
 
@@ -604,17 +608,17 @@ impl fmt::Debug for Variant {
     }
 }
 
-fn try_from_variant_relaxed<T: FromGodot>(variant: &Variant) -> Result<T, ConvertError> {
+fn try_from_variant_relaxed<T: EngineFromGodot>(variant: &Variant) -> Result<T, ConvertError> {
     let from_type = variant.get_type();
     let to_type = match ffi_variant_type::<T>() {
         ExtVariantType::Variant => {
             // Converting to Variant always succeeds.
-            return T::try_from_variant(variant);
+            return T::engine_try_from_variant(variant);
         }
         ExtVariantType::Concrete(to_type) if from_type == to_type => {
             // If types are the same, use the regular conversion.
             // This is both an optimization (avoids more FFI) and ensures consistency between strict and relaxed conversions for identical types.
-            return T::try_from_variant(variant);
+            return T::engine_try_from_variant(variant);
         }
         ExtVariantType::Concrete(to_type) => to_type,
     };
@@ -649,7 +653,7 @@ fn try_from_variant_relaxed<T: FromGodot>(variant: &Variant) -> Result<T, Conver
 
     // Try to convert the FFI types back to the user type. Can still fail, e.g. i64 -> i8.
     let via = <T::Via as GodotType>::try_from_ffi(ffi_result)?;
-    let concrete = T::try_from_godot(via)?;
+    let concrete = T::engine_try_from_godot(via)?;
 
     Ok(concrete)
 }

godot-core/src/meta/args/as_arg.rs

@@ -8,7 +8,7 @@
 use crate::builtin::{GString, NodePath, StringName, Variant};
 use crate::meta::sealed::Sealed;
 use crate::meta::traits::{GodotFfiVariant, GodotNullableFfi};
-use crate::meta::{CowArg, FfiArg, GodotType, ObjectArg, ToGodot};
+use crate::meta::{CowArg, EngineToGodot, FfiArg, GodotType, ObjectArg, ToGodot};
 use crate::obj::{DynGd, Gd, GodotClass, Inherits};
 
 /// Implicit conversions for arguments passed to Godot APIs.
@@ -595,21 +595,21 @@ pub trait ArgPassing: Sealed {
     #[doc(hidden)]
     fn ref_to_owned_via<T>(value: &T) -> T::Via
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: Clone;
 
     /// Convert to FFI repr in the most efficient way (move or borrow).
     #[doc(hidden)]
     fn ref_to_ffi<T>(value: &T) -> Self::FfiOutput<'_, T::Via>
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: GodotType;
 
     /// Convert to `Variant` in the most efficient way (move or borrow).
     #[doc(hidden)]
     fn ref_to_variant<T>(value: &T) -> Variant
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
     {
         let ffi_result = Self::ref_to_ffi(value);
         GodotFfiVariant::ffi_to_variant(&ffi_result)
@@ -631,19 +631,19 @@ impl ArgPassing for ByValue {
 
     fn ref_to_owned_via<T>(value: &T) -> T::Via
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: Clone,
     {
-        value.to_godot()
+        value.engine_to_godot()
     }
 
     fn ref_to_ffi<T>(value: &T) -> Self::FfiOutput<'_, T::Via>
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: GodotType,
     {
-        // For ByValue: to_godot() returns owned T::Via, move directly to FFI.
-        GodotType::into_ffi(value.to_godot())
+        // For ByValue: engine_to_godot() returns owned T::Via, move directly to FFI.
+        GodotType::into_ffi(value.engine_to_godot())
     }
 }
 
@@ -662,20 +662,20 @@ impl ArgPassing for ByRef {
 
     fn ref_to_owned_via<T>(value: &T) -> T::Via
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: Clone,
     {
         // For ByRef types, clone the reference to get owned value.
-        value.to_godot().clone()
+        value.engine_to_godot().clone()
     }
 
     fn ref_to_ffi<T>(value: &T) -> <T::Via as GodotType>::ToFfi<'_>
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: GodotType,
     {
         // Use by-ref conversion if possible, avoiding unnecessary clones when passing to FFI.
-        GodotType::to_ffi(value.to_godot())
+        GodotType::to_ffi(value.engine_to_godot())
     }
 }
 
@@ -696,19 +696,19 @@ impl ArgPassing for ByObject {
 
     fn ref_to_owned_via<T>(value: &T) -> T::Via
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: Clone,
     {
         // For ByObject types, do like ByRef: clone the reference to get owned value.
-        value.to_godot().clone()
+        value.engine_to_godot().clone()
     }
 
     fn ref_to_ffi<T>(value: &T) -> ObjectArg<'_>
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: GodotType,
     {
-        let obj_ref: &T::Via = value.to_godot(); // implements GodotType.
+        let obj_ref: &T::Via = value.engine_to_godot(); // implements GodotType.
         obj_ref.as_object_arg()
     }
 }
@@ -745,20 +745,20 @@ where
     // return: T::Via = Option<U::Via>
     fn ref_to_owned_via<T>(value: &T) -> T::Via
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: Clone,
     {
-        value.to_godot_owned()
+        value.engine_to_godot_owned()
     }
 
     fn ref_to_ffi<T>(value: &T) -> Self::FfiOutput<'_, T::Via>
     where
-        T: ToGodot<Pass = Self>,
+        T: EngineToGodot<Pass = Self>,
         T::Via: GodotType,
     {
         // Reuse pattern from impl GodotType for Option<T>:
         // Convert Option<&Via> to Option<Via::ToFfi> and then flatten to Via::ToFfi with null handling.
-        GodotNullableFfi::flatten_option(value.to_godot().map(|via_ref| via_ref.to_ffi()))
+        GodotNullableFfi::flatten_option(value.engine_to_godot().map(|via_ref| via_ref.to_ffi()))
     }
 }
 

godot-core/src/meta/error/convert_error.rs

@@ -277,7 +277,6 @@ pub(crate) enum FromFfiError {
     U16,
     I32,
     U32,
-    U64,
 }
 
 impl FromFfiError {
@@ -302,7 +301,6 @@ impl fmt::Display for FromFfiError {
             Self::U16 => "u16",
             Self::I32 => "i32",
             Self::U32 => "u32",
-            Self::U64 => "u64",
         };
 
         write!(f, "`{target}` cannot store the given value")
@@ -317,15 +315,15 @@ pub(crate) enum FromVariantError {
         actual: VariantType,
     },
 
-    /// Value cannot be represented in target type's domain.
-    BadValue,
-
     WrongClass {
         expected: ClassId,
     },
 
     /// Variant holds an object which is no longer alive.
     DeadObject,
+    //
+    // BadValue: Value cannot be represented in target type's domain.
+    // Used in the past for types like u64, with fallible FromVariant.
 }
 
 impl FromVariantError {
@@ -344,7 +342,6 @@ impl fmt::Display for FromVariantError {
                 // Note: wording is the same as in CallError::failed_param_conversion_engine()
                 write!(f, "cannot convert from {actual:?} to {expected:?}")
             }
-            Self::BadValue => write!(f, "value cannot be represented in target type's domain"),
             Self::WrongClass { expected } => {
                 write!(f, "cannot convert to class {expected}")
             }

godot-core/src/meta/godot_convert/impls.rs

@@ -9,7 +9,7 @@ use godot_ffi as sys;
 
 use crate::builtin::{Array, Variant};
 use crate::meta;
-use crate::meta::error::{ConvertError, ErrorKind, FromFfiError, FromVariantError};
+use crate::meta::error::{ConvertError, ErrorKind, FromFfiError};
 use crate::meta::{
     ArrayElement, ClassId, FromGodot, GodotConvert, GodotNullableFfi, GodotType, PropertyHintInfo,
     PropertyInfo, ToGodot,
@@ -331,47 +331,46 @@ impl GodotType for u64 {
     }
 
     fn try_from_ffi(ffi: Self::Ffi) -> Result<Self, ConvertError> {
-        // Ok(ffi as u64)
-        Self::try_from(ffi).map_err(|_rust_err| FromFfiError::U64.into_error(ffi))
+        Ok(ffi as u64)
     }
 
     impl_godot_scalar!(@shared_fns; i64, sys::GDEXTENSION_METHOD_ARGUMENT_METADATA_INT_IS_UINT64);
 }
 
+/// Test that `u64` does not implement `ToGodot/FromGodot`.
+///
+/// The impls are not provided since `u64` is not a natively supported type in GDScript (e.g. cannot be stored in a variant without altering the
+/// value). So `#[func]` does not support it. However, engine APIs may still need it, so there is codegen/macro support.
+///
+/// ```compile_fail
+/// # use godot::prelude::*;
+/// let value: u64 = 42;
+/// let variant = value.to_variant();  // Error: u64 does not implement ToGodot
+/// ```
 impl GodotConvert for u64 {
     type Via = u64;
 }
 
-impl ToGodot for u64 {
+// u64 implements internal-only conversion traits for use in engine APIs and virtual methods.
+impl meta::EngineToGodot for u64 {
     type Pass = meta::ByValue;
 
-    fn to_godot(&self) -> Self::Via {
+    fn engine_to_godot(&self) -> meta::ToArg<'_, Self::Via, Self::Pass> {
         *self
     }
 
-    fn to_variant(&self) -> Variant {
-        // TODO panic doesn't fit the trait's infallibility too well; maybe in the future try_to_godot/try_to_variant() methods are possible.
-        i64::try_from(*self)
-            .map(|v| v.to_variant())
-            .unwrap_or_else(|_| {
-                panic!("to_variant(): u64 value {self} is not representable inside Variant, which can only store i64 integers")
-            })
+    fn engine_to_variant(&self) -> Variant {
+        Variant::from(*self as i64) // Treat as i64.
     }
 }
 
-impl FromGodot for u64 {
-    fn try_from_godot(via: Self::Via) -> Result<Self, ConvertError> {
+impl meta::EngineFromGodot for u64 {
+    fn engine_try_from_godot(via: Self::Via) -> Result<Self, ConvertError> {
         Ok(via)
     }
 
-    fn try_from_variant(variant: &Variant) -> Result<Self, ConvertError> {
-        // Fail for values that are not representable as u64.
-        let value = variant.try_to::<i64>()?;
-
-        u64::try_from(value).map_err(|_rust_err| {
-            // TODO maybe use better error enumerator
-            FromVariantError::BadValue.into_error(value)
-        })
+    fn engine_try_from_variant(variant: &Variant) -> Result<Self, ConvertError> {
+        variant.try_to::<i64>().map(|i| i as u64)
     }
 }