stylo: Fix and ensure alignment of restyle hints. Test it on Travis.

Turns out eRestyle_LaterSiblings was not really matching, sigh...

.travis.yml

@@ -13,6 +13,7 @@ matrix:
       script:
          - ./mach build -d --verbose
          - ./mach build-geckolib
+         - ./mach test-geckolib
          - ./mach test-unit
          - ./mach test-compiletest
          - bash etc/ci/check_no_unwrap.sh

components/style/restyle_hints.rs

@@ -28,7 +28,7 @@ bitflags! {
         // of a good reason for that.
         const RESTYLE_DESCENDANTS = 0x02,
         #[doc = "Rerun selector matching on all later siblings of the element and all of their descendants."]
-        const RESTYLE_LATER_SIBLINGS = 0x04,
+        const RESTYLE_LATER_SIBLINGS = 0x08,
     }
 }
 

ports/geckolib/lib.rs

@@ -26,6 +26,7 @@ mod snapshot;
 mod snapshot_helpers;
 #[allow(non_snake_case)]
 pub mod glue;
+mod sanity_checks;
 mod traversal;
 mod wrapper;
 

ports/geckolib/sanity_checks.rs

@@ -0,0 +1,44 @@
+/* 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/. */
+
+//! Different static asserts that ensure the build does what it's expected to.
+//!
+//! TODO: maybe cfg(test) this?
+
+#![allow(unused_imports)]
+
+use std::mem;
+
+macro_rules! check_enum_value {
+    ($a:expr, $b:expr) => {
+        unsafe {
+            mem::transmute::<[u32; $a as usize],
+                             [u32; $b as usize]>([0; $a as usize]);
+        }
+    }
+}
+
+// NB: It's a shame we can't do this statically with bitflags, but no
+// const-fn and no other way to access the numerical value :-(
+macro_rules! check_enum_value_non_static {
+    ($a:expr, $b:expr) => {
+        assert_eq!($a as usize, $b as usize);
+    }
+}
+
+#[test]
+fn assert_restyle_hints_match() {
+    use style::restyle_hints::*; // For flags
+    use gecko_bindings::structs::nsRestyleHint;
+
+    check_enum_value_non_static!(nsRestyleHint::eRestyle_Self, RESTYLE_SELF.bits());
+    // XXX This for Servo actually means something like an hypothetical
+    // Restyle_AllDescendants (but without running selector matching on the
+    // element). ServoRestyleManager interprets it like that, but in practice we
+    // should align the behavior with Gecko adding a new restyle hint, maybe?
+    //
+    // See https://bugzilla.mozilla.org/show_bug.cgi?id=1291786
+    check_enum_value_non_static!(nsRestyleHint::eRestyle_SomeDescendants, RESTYLE_DESCENDANTS.bits());
+    check_enum_value_non_static!(nsRestyleHint::eRestyle_LaterSiblings, RESTYLE_LATER_SIBLINGS.bits());
+}

python/servo/testing_commands.py

@@ -158,6 +158,17 @@ class MachCommands(CommandBase):
                     return suite
         return None
 
+    @Command('test-geckolib',
+             description='Test geckolib sanity checks',
+             category='testing')
+    def test_geckolib(self):
+        self.ensure_bootstrapped()
+
+        env = self.build_env()
+        env["RUST_BACKTRACE"] = "1"
+
+        return call(["cargo", "test"], env=env, cwd=path.join("ports", "geckolib"))
+
     @Command('test-unit',
              description='Run unit tests',
              category='testing')