Give all impls a constness

Author: oli-obk

src/items.rs

@@ -961,6 +961,7 @@ fn format_impl_ref_and_type(
         of_trait,
         self_ty,
         items: _,
+        constness,
     } = iimpl;
     let mut result = String::with_capacity(128);
 
@@ -969,6 +970,8 @@ fn format_impl_ref_and_type(
     if let Some(of_trait) = of_trait.as_deref() {
         result.push_str(format_defaultness(of_trait.defaultness));
         result.push_str(format_safety(of_trait.safety));
+    } else {
+        result.push_str(format_constness_right(*constness));
     }
 
     let shape = if context.config.style_edition() >= StyleEdition::Edition2024 {
@@ -985,7 +988,7 @@ fn format_impl_ref_and_type(
 
     let trait_ref_overhead;
     if let Some(of_trait) = of_trait.as_deref() {
-        result.push_str(format_constness_right(of_trait.constness));
+        result.push_str(format_constness_right(*constness));
         let polarity_str = match of_trait.polarity {
             ast::ImplPolarity::Negative(_) => "!",
             ast::ImplPolarity::Positive => "",