Fix CopyTypes implementation for DeclarationId. (FuelLabs#2874)

This fixes a regression in CopyTypes which was preventing the mutated
declarations from reaching the `DeclarationEngine`.

After calling `copy_types` on the declaration we now replace it inside
the declaration engine.

Notes: this was found as part of debugging a test failure for
FuelLabs#2786. This fix makes the test
pass the type checking phase which it was failing, and now fails in IR
gen, so there's probably still issues around this or another related
area.

sway-core/src/concurrent_slab.rs

@@ -1,6 +1,10 @@
 use std::sync::RwLock;
 
-use crate::{type_system::TypeId, TypeInfo};
+use crate::{
+    declaration_engine::{declaration_id::DeclarationId, declaration_wrapper::DeclarationWrapper},
+    type_system::TypeId,
+    TypeInfo,
+};
 
 #[derive(Debug)]
 pub(crate) struct ConcurrentSlab<T> {
@@ -75,3 +79,15 @@ impl ConcurrentSlab<TypeInfo> {
         None
     }
 }
+
+impl ConcurrentSlab<DeclarationWrapper> {
+    pub fn replace(
+        &self,
+        index: DeclarationId,
+        new_value: DeclarationWrapper,
+    ) -> Option<DeclarationWrapper> {
+        let mut inner = self.inner.write().unwrap();
+        inner[*index] = new_value;
+        None
+    }
+}

sway-core/src/declaration_engine/declaration_engine.rs

@@ -37,6 +37,10 @@ impl DeclarationEngine {
         self.slab.get(*index)
     }
 
+    fn replace_decl_id(&self, index: DeclarationId, wrapper: DeclarationWrapper) {
+        self.slab.replace(index, wrapper);
+    }
+
     fn add_monomorphized_copy(&self, original_id: DeclarationId, new_id: DeclarationId) {
         let mut monomorphized_copies = self.monomorphized_copies.write().unwrap();
         match monomorphized_copies.get_mut(&*original_id) {
@@ -255,6 +259,10 @@ pub(crate) fn de_look_up_decl_id(index: DeclarationId) -> DeclarationWrapper {
     DECLARATION_ENGINE.look_up_decl_id(index)
 }
 
+pub(crate) fn de_replace_decl_id(index: DeclarationId, wrapper: DeclarationWrapper) {
+    DECLARATION_ENGINE.replace_decl_id(index, wrapper)
+}
+
 pub(crate) fn de_add_monomorphized_copy(original_id: DeclarationId, new_id: DeclarationId) {
     DECLARATION_ENGINE.add_monomorphized_copy(original_id, new_id);
 }

sway-core/src/declaration_engine/declaration_id.rs

@@ -4,7 +4,7 @@ use sway_types::{Span, Spanned};
 
 use crate::type_system::{CopyTypes, TypeMapping};
 
-use super::declaration_engine::de_look_up_decl_id;
+use super::declaration_engine::{de_look_up_decl_id, de_replace_decl_id};
 
 /// An ID used to refer to an item in the [DeclarationEngine](super::declaration_engine::DeclarationEngine)
 #[derive(Debug, Eq)]
@@ -53,7 +53,9 @@ impl Spanned for DeclarationId {
 
 impl CopyTypes for DeclarationId {
     fn copy_types(&mut self, type_mapping: &TypeMapping) {
-        de_look_up_decl_id(self.clone()).copy_types(type_mapping)
+        let mut decl = de_look_up_decl_id(self.clone());
+        decl.copy_types(type_mapping);
+        de_replace_decl_id(self.clone(), decl);
     }
 }