Add size_of_test crate

Cargo.lock

@@ -1407,6 +1407,7 @@ dependencies = [
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "layout 0.0.1",
  "script_layout_interface 0.0.1",
+ "size_of_test 0.0.1",
 ]
 
 [[package]]
@@ -2732,6 +2733,10 @@ name = "siphasher"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "size_of_test"
+version = "0.0.1"
+
 [[package]]
 name = "slab"
 version = "0.3.0"

components/size_of_test/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "size_of_test"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"

components/size_of_test/lib.rs

@@ -0,0 +1,28 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+#[macro_export]
+macro_rules! size_of_test {
+    ($testname: ident, $t: ty, $expected_size: expr) => {
+        #[test]
+        fn $testname() {
+            let new = ::std::mem::size_of::<$t>();
+            let old = $expected_size;
+            if new < old {
+                panic!(
+                    "Your changes have decreased the stack size of {} from {} to {}. \
+                     Good work! Please update the expected size in {}.",
+                    stringify!($t), old, new, file!()
+                )
+            } else if new > old {
+                panic!(
+                    "Your changes have increased the stack size of {} from {} to {}. \
+                     Please consider choosing a design which avoids this increase. \
+                     If you feel that the increase is necessary, update the size in {}.",
+                    stringify!($t), old, new, file!()
+                )
+            }
+        }
+    }
+}

tests/unit/layout/Cargo.toml

@@ -13,3 +13,4 @@ doctest = false
 atomic_refcell = "0.1"
 layout = {path = "../../../components/layout"}
 script_layout_interface = {path = "../../../components/script_layout_interface"}
+size_of_test = {path = "../../../components/size_of_test"}

tests/unit/layout/lib.rs

@@ -5,6 +5,7 @@
 extern crate atomic_refcell;
 extern crate layout;
 extern crate script_layout_interface;
+#[macro_use] extern crate size_of_test;
 
 #[cfg(test)] mod align_of;
 #[cfg(all(test, target_pointer_width = "64"))] mod size_of;

tests/unit/layout/size_of.rs

@@ -4,34 +4,6 @@
 
 use layout::Fragment;
 use layout::SpecificFragmentInfo;
-use std::mem::size_of;
 
-fn check_size_for(name: &'static str, expected: usize, actual: usize) {
-    if actual < expected {
-        panic!("Your changes have decreased the stack size of {} \
-                from {} to {}. Good work! Please update the size in tests/unit/layout/size_of.rs",
-                name, expected, actual);
-    }
-
-    if actual > expected {
-        panic!("Your changes have increased the stack size of {} \
-                from {} to {}.  Please consider choosing a design which avoids this increase. \
-                If you feel that the increase is necessary, update the size in \
-                tests/unit/layout/size_of.rs.",
-                name, expected, actual);
-    }
-}
-
-#[test]
-fn test_size_of_fragment() {
-    let expected = 160;
-    let actual = size_of::<Fragment>();
-    check_size_for("layout::fragment::Fragment", expected, actual);
-}
-
-#[test]
-fn test_size_of_specific_fragment_info() {
-    let expected = 24;
-    let actual = size_of::<SpecificFragmentInfo>();
-    check_size_for("layout::fragment::SpecificFragmentInfo", expected, actual);
-}
+size_of_test!(test_size_of_fragment, Fragment, 160);
+size_of_test!(test_size_of_specific_fragment_info, SpecificFragmentInfo, 24);