The attached testcase causes a crash in m-c rev 20170824-892c8916ba32 with stylo enabled by pref. thread '<unnamed>' panicked at 'Unexpected unit eStyleUnit_Calc', /home/worker/workspace/build/src/servo/components/style/gecko/values.rs:420 stack backtrace: 0: 0x7faf2a9423d3 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hcab99e0793da62c7 1: 0x7faf2a93d6f6 - std::sys_common::backtrace::_print::hbfe5b0c7e79c0711 2: 0x7faf2a94fa6a - std::panicking::default_hook::{{closure}}::h9ba2c6973907a2be 3: 0x7faf2a94f66b - std::panicking::default_hook::he4d55e2dd21c3cca 4: 0x7faf2a94feba - std::panicking::rust_panic_with_hook::ha138c05cd33ad44d 5: 0x7faf2a94fd54 - std::panicking::begin_panic::hcdbfa35c94142fa2 6: 0x7faf2a94fc89 - std::panicking::begin_panic_fmt::hc09fe500d9b7be81 7: 0x7faf2a4204ec - <style::values::generics::gecko::ScrollSnapPoint<style::values::computed[Parent 23721] WARNING: stylo: No docshell yet, assuming Gecko style system: file /home/worker/workspace/build/src/dom/base/nsDocument.cpp, line 13446 ::length::LengthOrPercentage> as style::gecko::values::GeckoStyleCoordConvertible>::from_gecko_style_coord::hc5d6c1237c56c4b6 8: 0x7faf2a663b6d - style::gecko_properties::<impl style::gecko_bindings::structs::root::mozilla::GeckoDisplay>::clone_scroll_snap_points_x::he31fb0ef9c0e8702 9: 0x7faf2a6348e1 - style::properties::animated_properties::AnimationValue::from_computed_values::h493ee6a2f1e7e722 10: 0x7faf2a1b6079 - Servo_ComputedValues_ExtractAnimationValue 11: 0x7faf27600d8c - mozilla::dom::KeyframeEffectReadOnly::EnsureBaseStyle(mozilla::AnimationProperty const&, mozilla::CSSPseudoElementType, nsPresContext*, mozilla::ServoStyleContext const*, RefPtr<mozilla::ServoStyleContext>&) 12: 0x7faf27605bcd - mozilla::dom::KeyframeEffectReadOnly::EnsureBaseStyles(mozilla::ServoStyleContext const*, nsTArray<mozilla::AnimationProperty> const&) 13: 0x7faf2761082e - void mozilla::dom::KeyframeEffectReadOnly::DoUpdateProperties<mozilla::ServoStyleContext const>(mozilla::ServoStyleContext const*) 14: 0x7faf27610a26 - void mozilla::dom::KeyframeEffectReadOnly::DoSetKeyframes<mozilla::ServoStyleContext const>(nsTArray<mozilla::Keyframe>&&, mozilla::ServoStyleContext const*) 15: 0x7faf27610f2f - mozilla::dom::KeyframeEffectReadOnly::SetKeyframes(JSContext*, JS::Handle<JSObject*>, mozilla::ErrorResult&) 16: 0x7faf27611213 - mozilla::dom::KeyframeEffect::Constructor(mozilla::dom::GlobalObject const&, mozilla::dom::Nullable<mozilla::dom::ElementOrCSSPseudoElement> const&, JS::Handle<JSObject*>, mozilla::dom::UnrestrictedDoubleOrKeyframeAnimationOptions const&, mozilla::ErrorResult&) 17: 0x7faf276b523d - mozilla::dom::Element::Animate(mozilla::dom::Nullable<mozilla::dom::ElementOrCSSPseudoElement> const&, JSContext*, JS::Handle<JSObject*>, mozilla::dom::UnrestrictedDoubleOrKeyframeAnimationOptions const&, mozilla::ErrorResult&) 18: 0x7faf276b5436 - mozilla::dom::Element::Animate(JSContext*, JS::Handle<JSObject*>, mozilla::dom::UnrestrictedDoubleOrKeyframeAnimationOptions const&, mozilla::ErrorResult&) 19: 0x7faf27cb4ded - mozilla::dom::ElementBinding::animate(JSContext*, JS::Handle<JSObject*>, mozilla::dom::Element*, JSJitMethodCallArgs const&) 20: 0x7faf27df491b - mozilla::dom::GenericBindingMethod(JSContext*, unsigned int, JS::Value*) 21: 0x7faf2973930c - js::CallJSNative(JSContext*, bool (*)(JSContext*, unsigned int, JS::Value*), JS::CallArgs const&)

have a patch

Pushed by manishearth@gmail.com: https://hg.mozilla.org/integration/autoland/rev/e796a86fc12f Add crashtest; r=emilio