don't special-case a single element record any more in updates

compiler/mono/src/ir.rs

@@ -3739,34 +3739,6 @@ pub fn with_hole<'a>(
             debug_assert_eq!(field_layouts.len(), symbols.len());
             debug_assert_eq!(fields.len(), symbols.len());
 
-            if symbols.len() == 1 {
-                // TODO we can probably special-case this more, skippiing the generation of
-                // UpdateExisting
-                let mut stmt = hole.clone();
-
-                let what_to_do = &fields[0];
-
-                match what_to_do {
-                    UpdateExisting(field) => {
-                        stmt = assign_to_symbol(
-                            env,
-                            procs,
-                            layout_cache,
-                            field.var,
-                            *field.loc_expr.clone(),
-                            assigned,
-                            stmt,
-                        );
-                    }
-                    CopyExisting(_) => {
-                        unreachable!(
-                            r"when a record has just one field and is updated, it must update that one field"
-                        );
-                    }
-                }
-
-                stmt
-            } else {
             let expr = Expr::Struct(symbols);
             let mut stmt = Stmt::Let(assigned, expr, record_layout, hole);
 
@@ -3791,14 +3763,12 @@ pub fn with_hole<'a>(
                             index,
                             field_layouts,
                         };
-                            stmt =
+                        stmt = Stmt::Let(*symbol, access_expr, *field_layout, arena.alloc(stmt));
-                                Stmt::Let(*symbol, access_expr, *field_layout, arena.alloc(stmt));
                     }
                 }
             }
             stmt
         }
-        }
 
         Closure {
             function_type,

compiler/test_gen/src/gen_records.rs

@@ -889,3 +889,26 @@ fn blue_and_absent() {
         i64
     );
 }
+
+#[test]
+fn update_the_only_field() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+            Model : { foo : I64 }
+
+            model : Model
+            model = { foo: 3 }
+
+            foo = 4
+
+            newModel : Model
+            newModel = { model & foo }
+
+            newModel.foo
+                "#
+        ),
+        4,
+        i64
+    );
+}