Apply suggestions from code review

Co-authored-by: Chayim Refael Friedman <chayimfr@gmail.com>

Author: Twil3akine

crates/hir-ty/src/infer/expr.rs

@@ -1186,13 +1186,7 @@ impl<'db> InferenceContext<'_, 'db> {
                 {
                     debug!(?remaining_fields);
 
-                    let missing_fields = variant_fields
-                        .fields()
-                        .iter()
-                        .filter_map(|(field_idx, field)| {
-                            remaining_fields.contains_key(&field.name).then_some(field_idx)
-                        })
-                        .collect::<Vec<_>>();
+                    let missing_fields = remaining_fields.values().copied().collect();
                     if !missing_fields.is_empty() {
                         self.push_diagnostic(InferenceDiagnostic::MissingFields {
                             expr,

crates/hir/src/diagnostics.rs

@@ -803,6 +803,7 @@ impl<'db> AnyDiagnostic<'db> {
                 let root = record.file_syntax(db);
                 let Either::Left(ast::Expr::RecordExpr(record_expr)) = record.value.to_node(&root)
                 else {
+                    never!("should always map to a `ast::RecordExpr`");
                     return None;
                 };