Add reflect_eq (#126)

### Checklist

* [x] I have read the [Contributor Guide](../../CONTRIBUTING.md)
* [x] I have read and agree to the [Code of
Conduct](../../CODE_OF_CONDUCT.md)
* [x] I have added a description of my changes and why I'd like them
included in the section below

### Description of Changes

A few times I've needed to compare `&dyn Reflect` values for equality.
Previously I did that by converting both to `Value`s but that might be
expensive so. This `reflect_eq` which walks each value without
allocating.

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
-- None.
+- **added:** Add `reflect_eq`
 
 # 0.1.15 (08. August, 2023)
 

crates/mirror-mirror-macros/src/derive_reflect/attrs.rs

@@ -55,7 +55,9 @@ impl ItemAttrs {
             .filter(|attr| attr.meta.path().is_ident("reflect"))
             .peekable();
 
-        let Some(attr) = reflect_attrs.next() else { return Ok(Self::new(docs)) };
+        let Some(attr) = reflect_attrs.next() else {
+            return Ok(Self::new(docs));
+        };
 
         if let Some(next) = reflect_attrs.peek() {
             return Err(syn::Error::new_spanned(
@@ -177,8 +179,12 @@ fn parse_docs(attrs: &[Attribute]) -> Vec<LitStr> {
         .filter(|attr| attr.meta.path().is_ident("doc"))
         .filter_map(|attr| {
             let name_value = attr.meta.require_name_value().ok()?;
-            let Expr::Lit(lit_expr) = &name_value.value else { return None };
-            let Lit::Str(lit_str) = &lit_expr.lit else { return None };
+            let Expr::Lit(lit_expr) = &name_value.value else {
+                return None;
+            };
+            let Lit::Str(lit_str) = &lit_expr.lit else {
+                return None;
+            };
             Some(lit_str.clone())
         })
         .collect::<Vec<_>>()
@@ -296,7 +302,9 @@ impl InnerAttrs {
             .filter(|attr| attr.meta.path().is_ident("reflect"))
             .peekable();
 
-        let Some(attr) = reflect_attrs.next() else { return Ok(Self::new(docs)) };
+        let Some(attr) = reflect_attrs.next() else {
+            return Ok(Self::new(docs));
+        };
 
         if let Some(next) = reflect_attrs.peek() {
             return Err(syn::Error::new_spanned(

crates/mirror-mirror/src/foreign_impls/via_scalar.rs

@@ -27,10 +27,12 @@ macro_rules! impl_reflect_via_scalar {
             impl Reflect for $ty {
                 trivial_reflect_methods!();
 
+                #[allow(clippy::redundant_closure_call)]
                 fn reflect_owned(self: Box<Self>) -> ReflectOwned {
                     ReflectOwned::Scalar(ScalarOwned::from($get_fn(&*self)))
                 }
 
+                #[allow(clippy::redundant_closure_call)]
                 fn reflect_ref(&self) -> ReflectRef<'_> {
                     ReflectRef::Scalar(ScalarRef::from($get_fn(self)))
                 }
@@ -45,6 +47,7 @@ macro_rules! impl_reflect_via_scalar {
                     }
                 }
 
+                #[allow(clippy::redundant_closure_call)]
                 fn to_value(&self) -> Value {
                     $get_fn(self).to_value()
                 }

crates/mirror-mirror/src/lib.rs

@@ -334,6 +334,9 @@ pub mod value;
 pub mod try_visit;
 
 mod foreign_impls;
+mod reflect_eq;
+
+pub use reflect_eq::reflect_eq;
 
 #[cfg(feature = "std")]
 #[cfg(test)]
@@ -535,6 +538,12 @@ impl fmt::Debug for dyn Reflect {
     }
 }
 
+impl PartialEq for dyn Reflect {
+    fn eq(&self, other: &Self) -> bool {
+        reflect_eq(self, other).unwrap_or(false)
+    }
+}
+
 macro_rules! impl_for_core_types {
     ($($ty:ident)*) => {
         $(
@@ -972,7 +981,7 @@ impl<'a> ReflectRef<'a> {
 }
 
 /// An immutable reflected scalar value.
-#[derive(Debug, Copy, Clone)]
+#[derive(Debug, Copy, Clone, PartialEq)]
 #[allow(non_camel_case_types)]
 pub enum ScalarRef<'a> {
     usize(usize),