Improve AsArg<T> compile error messages by using marker traits

godot-codegen/src/generator/functions_common.rs

@@ -477,8 +477,10 @@ pub(crate) fn make_param_or_field_type(
             special_ty = Some(quote! { CowArg<#lft, #ty> });
 
             match decl {
-                FnParamDecl::FnPublic => quote! { impl AsArg<#ty> },
-                FnParamDecl::FnPublicLifetime => quote! { impl AsArg<#ty> + 'ex },
+                FnParamDecl::FnPublic => quote! { impl AsArg<#ty> + ShouldBePassedAsRef },
+                FnParamDecl::FnPublicLifetime => {
+                    quote! { impl AsArg<#ty> + ShouldBePassedAsRef + 'ex }
+                }
                 FnParamDecl::FnInternal => quote! { CowArg<#ty> },
                 FnParamDecl::Field => quote! { CowArg<'ex, #ty> },
             }

godot-codegen/src/util.rs

@@ -25,7 +25,7 @@ pub fn make_imports() -> TokenStream {
     quote! {
         use godot_ffi as sys;
         use crate::builtin::*;
-        use crate::meta::{AsArg, ClassId, CowArg, InParamTuple, OutParamTuple, ParamTuple, RawPtr, RefArg, Signature};
+        use crate::meta::{AsArg, ClassId, CowArg, InParamTuple, OutParamTuple, ParamTuple, RawPtr, RefArg, ShouldBePassedAsRef, Signature};
         use crate::classes::native::*;
         use crate::classes::Object;
         use crate::obj::Gd;

godot-core/src/builtin/callable.rs

@@ -12,7 +12,7 @@ use godot_ffi as sys;
 use sys::{ffi_methods, ExtVariantType, GodotFfi};
 
 use crate::builtin::{inner, AnyArray, CowStr, StringName, Variant};
-use crate::meta::{GodotType, ToGodot};
+use crate::meta::{GodotType, ShouldBePassedAsRef, ToGodot};
 use crate::obj::bounds::DynMemory;
 use crate::obj::{Bounds, Gd, GodotClass, InstanceId, Singleton};
 use crate::{classes, meta};
@@ -51,7 +51,7 @@ impl Callable {
     pub fn from_object_method<T, S>(object: &Gd<T>, method_name: S) -> Self
     where
         T: GodotClass, // + Inherits<Object>,
-        S: meta::AsArg<StringName>,
+        S: meta::AsArg<StringName> + ShouldBePassedAsRef,
     {
         meta::arg_into_ref!(method_name);
 
@@ -79,7 +79,7 @@ impl Callable {
     #[cfg(since_api = "4.3")]
     pub fn from_variant_method<S>(variant: &Variant, method_name: S) -> Self
     where
-        S: meta::AsArg<StringName>,
+        S: meta::AsArg<StringName> + ShouldBePassedAsRef,
     {
         meta::arg_into_ref!(method_name);
         inner::InnerCallable::create(variant, method_name)
@@ -94,8 +94,8 @@ impl Callable {
     /// reflection APIs at the moment.
     #[cfg(since_api = "4.4")]
     pub fn from_class_static(
-        class_name: impl meta::AsArg<StringName>,
-        function_name: impl meta::AsArg<StringName>,
+        class_name: impl meta::AsArg<StringName> + ShouldBePassedAsRef,
+        function_name: impl meta::AsArg<StringName> + ShouldBePassedAsRef,
     ) -> Self {
         meta::arg_into_owned!(class_name);
         meta::arg_into_owned!(function_name);
@@ -125,8 +125,8 @@ impl Callable {
     #[deprecated = "Renamed to `from_class_static`."]
     #[cfg(since_api = "4.4")]
     pub fn from_local_static(
-        class_name: impl meta::AsArg<StringName>,
-        function_name: impl meta::AsArg<StringName>,
+        class_name: impl meta::AsArg<StringName> + ShouldBePassedAsRef,
+        function_name: impl meta::AsArg<StringName> + ShouldBePassedAsRef,
     ) -> Self {
         Self::from_class_static(class_name, function_name)
     }

godot-core/src/builtin/signal.rs

@@ -15,7 +15,7 @@ use crate::classes::object::ConnectFlags;
 use crate::classes::Object;
 use crate::global::Error;
 use crate::meta;
-use crate::meta::{FromGodot, GodotType, ToGodot};
+use crate::meta::{FromGodot, GodotType, ShouldBePassedAsRef, ToGodot};
 use crate::obj::bounds::DynMemory;
 use crate::obj::{Bounds, EngineBitfield, Gd, GodotClass, InstanceId};
 
@@ -42,7 +42,7 @@ impl Signal {
     pub fn from_object_signal<T, S>(object: &Gd<T>, signal_name: S) -> Self
     where
         T: GodotClass,
-        S: meta::AsArg<StringName>,
+        S: meta::AsArg<StringName> + ShouldBePassedAsRef,
     {
         meta::arg_into_ref!(signal_name);
 

godot-core/src/builtin/strings/gstring.rs

@@ -16,7 +16,7 @@ use sys::{ffi_methods, interface_fn, ExtVariantType, GodotFfi};
 use crate::builtin::strings::{pad_if_needed, Encoding};
 use crate::builtin::{inner, NodePath, StringName, Variant};
 use crate::meta::error::StringError;
-use crate::meta::AsArg;
+use crate::meta::{AsArg, ShouldBePassedAsRef};
 use crate::{impl_shared_string_api, meta};
 
 /// Godot's reference counted string type.

godot-core/src/builtin/strings/string_macros.rs

@@ -37,7 +37,7 @@ macro_rules! impl_shared_string_api {
             /// Find first occurrence of `what` and return index, or `None` if not found.
             ///
             /// Check [`find_ex()`](Self::find_ex) for all custom options.
-            pub fn find(&self, what: impl AsArg<GString>) -> Option<usize> {
+            pub fn find(&self, what: impl AsArg<GString> + ShouldBePassedAsRef) -> Option<usize> {
                 self.find_ex(what).done()
             }
 
@@ -73,7 +73,7 @@ macro_rules! impl_shared_string_api {
             #[doc(alias = "findn", alias = "rfind", alias = "rfindn")]
             pub fn find_ex<'s, 'w>(
                 &'s self,
-                what: impl AsArg<GString> + 'w,
+                what: impl AsArg<GString> + ShouldBePassedAsRef + 'w,
             ) -> ExFind<'s, 'w> {
                 ExFind::new(self, what.into_arg())
             }
@@ -93,7 +93,7 @@ macro_rules! impl_shared_string_api {
             /// Splits the string according to `delimiter`.
             ///
             /// See [`split_ex()`][Self::split_ex] if you need further configuration.
-            pub fn split(&self, delimiter: impl AsArg<GString>) -> $crate::builtin::PackedStringArray {
+            pub fn split(&self, delimiter: impl AsArg<GString> + ShouldBePassedAsRef) -> $crate::builtin::PackedStringArray {
                 self.split_ex(delimiter).done()
             }
 
@@ -132,7 +132,7 @@ macro_rules! impl_shared_string_api {
             /// This is faster than [`split()`][Self::split], if you only need one substring.
             pub fn get_slice(
                 &self,
-                delimiter: impl AsArg<GString>,
+                delimiter: impl AsArg<GString> + ShouldBePassedAsRef,
                 slice: usize,
             ) -> Option<GString> {
                 let sliced = self.as_inner().get_slice(delimiter, slice as i64);
@@ -156,7 +156,7 @@ macro_rules! impl_shared_string_api {
             /// Returns the total number of slices, when the string is split with the given delimiter.
             ///
             /// See also [`split()`][Self::split] and [`get_slice()`][Self::get_slice].
-            pub fn get_slice_count(&self, delimiter: impl AsArg<GString>) -> usize {
+            pub fn get_slice_count(&self, delimiter: impl AsArg<GString> + ShouldBePassedAsRef) -> usize {
                 self.as_inner().get_slice_count(delimiter) as usize
             }
 
@@ -171,7 +171,7 @@ macro_rules! impl_shared_string_api {
             /// If the position is out of bounds, the string will be inserted at the end.
             ///
             /// Consider using [`format()`](Self::format) for more flexibility.
-            pub fn insert(&self, position: usize, what: impl AsArg<GString>) -> GString {
+            pub fn insert(&self, position: usize, what: impl AsArg<GString> + ShouldBePassedAsRef) -> GString {
                 self.as_inner().insert(position as i64, what)
             }
 
@@ -188,7 +188,7 @@ macro_rules! impl_shared_string_api {
             pub fn format_with_placeholder(
                 &self,
                 array_or_dict: &Variant,
-                placeholder: impl AsArg<GString>,
+                placeholder: impl AsArg<GString> + ShouldBePassedAsRef,
             ) -> GString {
                 self.as_inner().format(array_or_dict, placeholder)
             }
@@ -233,7 +233,7 @@ macro_rules! impl_shared_string_api {
             /// roughly matches the alphabetical order.
             ///
             /// See also [`nocasecmp_to()`](Self::nocasecmp_to), [`naturalcasecmp_to()`](Self::naturalcasecmp_to), [`filecasecmp_to()`](Self::filecasecmp_to).
-            pub fn casecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn casecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().casecmp_to(to))
             }
 
@@ -243,7 +243,7 @@ macro_rules! impl_shared_string_api {
             /// roughly matches the alphabetical order.
             ///
             /// See also [`casecmp_to()`](Self::casecmp_to), [`naturalcasecmp_to()`](Self::naturalcasecmp_to), [`filecasecmp_to()`](Self::filecasecmp_to).
-            pub fn nocasecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn nocasecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().nocasecmp_to(to))
             }
 
@@ -260,7 +260,7 @@ macro_rules! impl_shared_string_api {
             /// if shorter.
             ///
             /// See also [`casecmp_to()`](Self::casecmp_to), [`naturalnocasecmp_to()`](Self::naturalnocasecmp_to), [`filecasecmp_to()`](Self::filecasecmp_to).
-            pub fn naturalcasecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn naturalcasecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().naturalcasecmp_to(to))
             }
 
@@ -277,7 +277,7 @@ macro_rules! impl_shared_string_api {
             /// if shorter.
             ///
             /// See also [`casecmp_to()`](Self::casecmp_to), [`naturalcasecmp_to()`](Self::naturalcasecmp_to), [`filecasecmp_to()`](Self::filecasecmp_to).
-            pub fn naturalnocasecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn naturalnocasecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().naturalnocasecmp_to(to))
             }
 
@@ -288,7 +288,7 @@ macro_rules! impl_shared_string_api {
             ///
             /// See also [`casecmp_to()`](Self::casecmp_to), [`naturalcasecmp_to()`](Self::naturalcasecmp_to), [`filenocasecmp_to()`](Self::filenocasecmp_to).
             #[cfg(since_api = "4.3")]
-            pub fn filecasecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn filecasecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().filecasecmp_to(to))
             }
 
@@ -299,7 +299,7 @@ macro_rules! impl_shared_string_api {
             ///
             /// See also [`casecmp_to()`](Self::casecmp_to), [`naturalcasecmp_to()`](Self::naturalcasecmp_to), [`filecasecmp_to()`](Self::filecasecmp_to).
             #[cfg(since_api = "4.3")]
-            pub fn filenocasecmp_to(&self, to: impl AsArg<GString>) -> std::cmp::Ordering {
+            pub fn filenocasecmp_to(&self, to: impl AsArg<GString> + ShouldBePassedAsRef) -> std::cmp::Ordering {
                 sys::i64_to_ordering(self.as_inner().filenocasecmp_to(to))
             }
 
@@ -310,7 +310,7 @@ macro_rules! impl_shared_string_api {
             ///
             /// Renamed from `match` because of collision with Rust keyword + possible confusion with `String::matches()` that can match regex.
             #[doc(alias = "match")]
-            pub fn match_glob(&self, pattern: impl AsArg<GString>) -> bool {
+            pub fn match_glob(&self, pattern: impl AsArg<GString> + ShouldBePassedAsRef) -> bool {
                 self.as_inner().match_(pattern)
             }
 
@@ -321,7 +321,7 @@ macro_rules! impl_shared_string_api {
             ///
             /// Renamed from `matchn` because of collision with Rust keyword + possible confusion with `String::matches()` that can match regex.
             #[doc(alias = "matchn")]
-            pub fn matchn_glob(&self, pattern: impl AsArg<GString>) -> bool {
+            pub fn matchn_glob(&self, pattern: impl AsArg<GString> + ShouldBePassedAsRef) -> bool {
                 self.as_inner().matchn(pattern)
             }
         }

godot-core/src/builtin/strings/string_name.rs

@@ -12,7 +12,7 @@ use sys::{ffi_methods, ExtVariantType, GodotFfi};
 
 use crate::builtin::{inner, Encoding, GString, NodePath, Variant};
 use crate::meta::error::StringError;
-use crate::meta::AsArg;
+use crate::meta::{AsArg, ShouldBePassedAsRef};
 use crate::{impl_shared_string_api, meta};
 
 /// A string optimized for unique names.

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

@@ -17,7 +17,7 @@ use crate::classes;
 use crate::meta::error::{ConvertError, FromVariantError};
 use crate::meta::{
     arg_into_ref, ffi_variant_type, ArrayElement, AsArg, EngineFromGodot, ExtVariantType,
-    FromGodot, GodotType, ToGodot,
+    FromGodot, GodotType, ShouldBePassedAsRef, ToGodot,
 };
 
 mod impls;
@@ -232,7 +232,11 @@ impl Variant {
     /// * If the method does not exist or the signature is not compatible with the passed arguments.
     /// * If the call causes an error.
     #[inline]
-    pub fn call(&self, method: impl AsArg<StringName>, args: &[Variant]) -> Variant {
+    pub fn call(
+        &self,
+        method: impl AsArg<StringName> + ShouldBePassedAsRef,
+        args: &[Variant],
+    ) -> Variant {
         arg_into_ref!(method);
         self.call_inner(method, args)
     }

godot-core/src/classes/type_safe_replacements.rs

@@ -17,7 +17,7 @@ use crate::classes::object::ConnectFlags;
 use crate::classes::scene_tree::GroupCallFlags;
 use crate::classes::{Object, SceneTree, Script};
 use crate::global::Error;
-use crate::meta::{arg_into_ref, AsArg, ToGodot};
+use crate::meta::{arg_into_ref, AsArg, ShouldBePassedAsRef, ToGodot};
 use crate::obj::{EngineBitfield, Gd};
 
 impl Object {
@@ -36,13 +36,17 @@ impl Object {
         self.raw_set_script(&script.to_variant());
     }
 
-    pub fn connect(&mut self, signal: impl AsArg<StringName>, callable: &Callable) -> Error {
+    pub fn connect(
+        &mut self,
+        signal: impl AsArg<StringName> + ShouldBePassedAsRef,
+        callable: &Callable,
+    ) -> Error {
         self.raw_connect(signal, callable)
     }
 
     pub fn connect_flags(
         &mut self,
-        signal: impl AsArg<StringName>,
+        signal: impl AsArg<StringName> + ShouldBePassedAsRef,
         callable: &Callable,
         flags: ConnectFlags,
     ) -> Error {
@@ -59,8 +63,8 @@ impl SceneTree {
     pub fn call_group_flags(
         &mut self,
         flags: GroupCallFlags,
-        group: impl AsArg<StringName>,
-        method: impl AsArg<StringName>,
+        group: impl AsArg<StringName> + ShouldBePassedAsRef,
+        method: impl AsArg<StringName> + ShouldBePassedAsRef,
         varargs: &[Variant],
     ) {
         self.raw_call_group_flags(flags.ord() as i64, group, method, varargs)
@@ -69,23 +73,27 @@ impl SceneTree {
     pub fn set_group_flags(
         &mut self,
         call_flags: GroupCallFlags,
-        group: impl AsArg<StringName>,
-        property: impl AsArg<GString>,
+        group: impl AsArg<StringName> + ShouldBePassedAsRef,
+        property: impl AsArg<GString> + ShouldBePassedAsRef,
         value: &Variant,
     ) {
         self.raw_set_group_flags(call_flags.ord() as u32, group, property, value)
     }
 
     /// Assumes notifications of `Node`. To relay those of derived constants, use [`NodeNotification::Unknown`].
-    pub fn notify_group(&mut self, group: impl AsArg<StringName>, notification: NodeNotification) {
+    pub fn notify_group(
+        &mut self,
+        group: impl AsArg<StringName> + ShouldBePassedAsRef,
+        notification: NodeNotification,
+    ) {
         self.raw_notify_group(group, notification.into())
     }
 
     /// Assumes notifications of `Node`. To relay those of derived constants, use [`NodeNotification::Unknown`].
     pub fn notify_group_flags(
         &mut self,
         call_flags: GroupCallFlags,
-        group: impl AsArg<StringName>,
+        group: impl AsArg<StringName> + ShouldBePassedAsRef,
         notification: NodeNotification,
     ) {
         self.raw_notify_group_flags(call_flags.ord() as u32, group, notification.into())