stop scope diffing in when canonicalization

compiler/can/src/expr.rs

@@ -1099,23 +1099,17 @@ fn canonicalize_when_branch<'a>(
         }
     };
 
-    // Now that we've collected all the references for this branch, check to see if
-    // any of the new idents it defined were unused. If any were, report it.
-    for (symbol, region) in scope.symbols() {
-        let symbol = *symbol;
-
-        if !output.references.has_type_or_value_lookup(symbol)
-            && !branch_output.references.has_type_or_value_lookup(symbol)
-            && !original_scope.contains_symbol(symbol)
-            && !scope.abilities_store.is_specialization_name(symbol)
-        {
-            env.problem(Problem::UnusedDef(symbol, *region));
-        }
-    }
-
     let references = branch_output.references.clone();
     output.union(branch_output);
 
+    // Now that we've collected all the references for this branch, check to see if
+    // any of the new idents it defined were unused. If any were, report it.
+    for (symbol, region) in bindings_from_patterns(patterns.iter()) {
+        if !output.references.has_value_lookup(symbol) {
+            env.problem(Problem::UnusedDef(symbol, region));
+        }
+    }
+
     (
         WhenBranch {
             patterns,

compiler/can/src/pattern.rs

@@ -687,12 +687,15 @@ fn add_bindings_from_patterns(
             add_bindings_from_patterns(&loc_arg.region, &loc_arg.value, answer);
         }
         RecordDestructure { destructs, .. } => {
-            for Loc {
+            for loc_destruct in destructs {
-                region,
+                match loc_destruct.value.typ {
-                value: RecordDestruct { symbol, .. },
+                    DestructType::Required | DestructType::Optional(_, _) => {
-            } in destructs
+                        answer.push((loc_destruct.value.symbol, loc_destruct.region));
-            {
+                    }
-                answer.push((*symbol, *region));
+                    DestructType::Guard(_, _) => {
+                        // a guard does not introduce the symbol
+                    }
+                }
             }
         }
         NumLiteral(..)

compiler/can/src/scope.rs

@@ -104,10 +104,6 @@ impl Scope {
         self.idents.contains_key(ident)
     }
 
-    pub fn contains_symbol(&self, symbol: Symbol) -> bool {
-        self.symbols.contains_key(&symbol)
-    }
-
     pub fn num_idents(&self) -> usize {
         self.idents.len()
     }