From ba987ef60d3f3f8c3742404747ee14b17475311b Mon Sep 17 00:00:00 2001
From: Gino Valente <gino.valente.code@gmail.com>
Date: Mon, 2 Sep 2024 16:49:34 -0700
Subject: [PATCH] Added `Signature` and `ArgumentSignature` types

---
 crates/bevy_reflect/src/func/mod.rs       |   1 +
 crates/bevy_reflect/src/func/signature.rs | 142 ++++++++++++++++++++++
 2 files changed, 143 insertions(+)
 create mode 100644 crates/bevy_reflect/src/func/signature.rs

diff --git a/crates/bevy_reflect/src/func/mod.rs b/crates/bevy_reflect/src/func/mod.rs
index 2811f5c226..b21b78d914 100644
--- a/crates/bevy_reflect/src/func/mod.rs
+++ b/crates/bevy_reflect/src/func/mod.rs
@@ -154,6 +154,7 @@ mod reflect_fn;
 mod reflect_fn_mut;
 mod registry;
 mod return_type;
+pub mod signature;
 
 #[cfg(test)]
 mod tests {
diff --git a/crates/bevy_reflect/src/func/signature.rs b/crates/bevy_reflect/src/func/signature.rs
new file mode 100644
index 0000000000..eaea303d1b
--- /dev/null
+++ b/crates/bevy_reflect/src/func/signature.rs
@@ -0,0 +1,142 @@
+//! Function signature types.
+//!
+//! Function signatures differ from [`FunctionInfo`] in that they are only concerned
+//! about the types and order of the arguments and return type of a function.
+//!
+//! The names of arguments do not matter,
+//! nor does any other information about the function such as its name or other attributes.
+//!
+//! This makes signatures useful for comparing or hashing functions strictly based on their
+//! arguments and return type.
+
+use crate::func::args::ArgInfo;
+use crate::func::FunctionInfo;
+use crate::Type;
+use core::borrow::Borrow;
+use core::fmt::{Debug, Formatter};
+use core::ops::{Deref, DerefMut};
+
+/// The signature of a function.
+///
+/// This can be used as a way to compare or hash functions based on their arguments and return type.
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct Signature {
+    args: ArgumentSignature,
+    ret: Type,
+}
+
+impl Signature {
+    /// Create a new function signature with the given argument signature and return type.
+    pub fn new(args: ArgumentSignature, ret: Type) -> Self {
+        Self { args, ret }
+    }
+
+    /// Get the argument signature of the function.
+    pub fn args(&self) -> &ArgumentSignature {
+        &self.args
+    }
+
+    /// Get the return type of the function.
+    pub fn return_type(&self) -> &Type {
+        &self.ret
+    }
+}
+
+impl Debug for Signature {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        write!(f, "{:?} -> {:?}", self.args, self.ret)
+    }
+}
+
+impl<T: Borrow<FunctionInfo>> From<T> for Signature {
+    fn from(info: T) -> Self {
+        let info = info.borrow();
+        Self::new(ArgumentSignature::from(info), *info.return_info().ty())
+    }
+}
+
+/// The argument-portion of a function signature.
+///
+/// For example, given a function signature `(a: i32, b: f32) -> u32`,
+/// the argument signature would be `(i32, f32)`.
+///
+/// This can be used as a way to compare or hash functions based on their arguments.
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct ArgumentSignature(Box<[Type]>);
+
+impl Debug for ArgumentSignature {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
+        let mut tuple = f.debug_tuple("");
+        for ty in self.0.iter() {
+            tuple.field(ty);
+        }
+        tuple.finish()
+    }
+}
+
+impl Deref for ArgumentSignature {
+    type Target = [Type];
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for ArgumentSignature {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl FromIterator<Type> for ArgumentSignature {
+    fn from_iter<T: IntoIterator<Item = Type>>(iter: T) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
+impl<T: Borrow<FunctionInfo>> From<T> for ArgumentSignature {
+    fn from(info: T) -> Self {
+        Self(
+            info.borrow()
+                .args()
+                .iter()
+                .map(ArgInfo::ty)
+                .copied()
+                .collect(),
+        )
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::func::TypedFunction;
+
+    #[test]
+    fn should_generate_signature_from_function_info() {
+        fn add(a: i32, b: f32) -> u32 {
+            (a as f32 + b).round() as u32
+        }
+
+        let info = add.get_function_info();
+        let signature = Signature::from(&info);
+
+        assert_eq!(signature.args().0.len(), 2);
+        assert_eq!(signature.args().0[0], Type::of::<i32>());
+        assert_eq!(signature.args().0[1], Type::of::<f32>());
+        assert_eq!(*signature.return_type(), Type::of::<u32>());
+    }
+
+    #[test]
+    fn should_debug_signature() {
+        let signature = Signature::new(
+            ArgumentSignature::from_iter(vec![Type::of::<&mut String>(), Type::of::<i32>()]),
+            Type::of::<()>(),
+        );
+
+        assert_eq!(
+            format!("{:?}", signature),
+            "(&mut alloc::string::String, i32) -> ()"
+        );
+    }
+}