1 files changed, 50 insertions, 0 deletions
diff --git a/servo/ports/geckolib/tests/specified_values.rs b/servo/ports/geckolib/tests/specified_values.rs
new file mode 100644
index 0000000000..744bf1fd80
--- /dev/null
+++ b/servo/ports/geckolib/tests/specified_values.rs
@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#[cfg(all(test, target_pointer_width = "64"))]
+#[test]
+fn size_of_specified_values() {
+    use std::mem::size_of;
+    use style;
+
+    let threshold = 24;
+
+    let mut bad_properties = vec![];
+
+    macro_rules! check_property {
+        ( $( { $name: ident, $boxed: expr } )+ ) => {
+            $(
+                let size = size_of::<style::properties::longhands::$name::SpecifiedValue>();
+                let is_boxed = $boxed;
+                if (!is_boxed && size > threshold) || (is_boxed && size <= threshold) {
+                    bad_properties.push((stringify!($name), size, is_boxed));
+                }
+            )+
+        }
+    }
+
+    longhand_properties_idents!(check_property);
+
+    let mut failing_messages = vec![];
+
+    for bad_prop in bad_properties {
+        if !bad_prop.2 {
+            failing_messages.push(
+                format!("Your changes have increased the size of {} SpecifiedValue to {}. The threshold is \
+                        currently {}. SpecifiedValues affect size of PropertyDeclaration enum and \
+                        increasing the size may negative affect style system performance. Please consider \
+                        using `boxed=\"True\"` in this longhand.",
+                        bad_prop.0, bad_prop.1, threshold));
+        } else if bad_prop.2 {
+            failing_messages.push(
+                format!("Your changes have decreased the size of {} SpecifiedValue to {}. Good work! \
+                        The threshold is currently {}. Please consider removing `boxed=\"True\"` from this longhand.",
+                        bad_prop.0, bad_prop.1, threshold));
+        }
+    }
+
+    if !failing_messages.is_empty() {
+        panic!("{}", failing_messages.join("\n\n"));
+    }
+}