Add flags to longhands for gecko glue

The flags are creates_stacking_context, fixpos_cb and abspos_cb. These will be needed in will-change glue.

components/style/properties/data.py

@@ -96,7 +96,8 @@ class Longhand(object):
                  predefined_type=None, custom_cascade=False, experimental=False, internal=False,
                  need_clone=False, need_index=False, gecko_ffi_name=None, depend_on_viewport_size=False,
                  allowed_in_keyframe_block=True, complex_color=False, cast_type='u8',
-                 has_uncacheable_values=False, logical=False, alias=None, extra_prefixes=None, boxed=False):
+                 has_uncacheable_values=False, logical=False, alias=None, extra_prefixes=None, boxed=False,
+                 creates_stacking_context=False, fixpos_cb=False, abspos_cb=False):
         self.name = name
         if not spec:
             raise TypeError("Spec should be specified for %s" % name)
@@ -120,6 +121,9 @@ class Longhand(object):
         self.alias = alias.split() if alias else []
         self.extra_prefixes = extra_prefixes.split() if extra_prefixes else []
         self.boxed = arg_to_bool(boxed)
+        self.creates_stacking_context = arg_to_bool(creates_stacking_context)
+        self.fixpos_cb = arg_to_bool(fixpos_cb)
+        self.abspos_cb = arg_to_bool(abspos_cb)
 
         # https://drafts.csswg.org/css-animations/#keyframes
         # > The <declaration-list> inside of <keyframe-block> accepts any CSS property

components/style/properties/longhand/box.mako.rs

@@ -108,6 +108,8 @@ ${helpers.single_keyword("-moz-top-layer", "none top",
                                   need_clone="True"
                                   extra_gecko_values="sticky"
                                   animatable="False"
+                                  creates_stacking_context="True"
+                                  abspos_cb="True"
                                   spec="https://drafts.csswg.org/css-position/#position-property">
     impl SpecifiedValue {
         pub fn is_absolutely_positioned_style(&self) -> bool {
@@ -1116,6 +1118,8 @@ ${helpers.predefined_type("scroll-snap-coordinate",
 
 <%helpers:longhand name="transform" products="gecko servo" extra_prefixes="webkit"
                    animatable="True"
+                   creates_stacking_context="True"
+                   fixpos_cb="True"
                    spec="https://drafts.csswg.org/css-transforms/#propdef-transform">
     use app_units::Au;
     use style_traits::ToCss;
@@ -1672,6 +1676,7 @@ ${helpers.single_keyword("isolation",
                          "auto isolate",
                          products="gecko",
                          spec="https://drafts.fxtf.org/compositing/#isolation",
+                         creates_stacking_context=True,
                          animatable=False)}
 
 // TODO add support for logical values recto and verso
@@ -1710,6 +1715,8 @@ ${helpers.predefined_type("perspective",
                           spec="https://drafts.csswg.org/css-transforms/#perspective",
                           extra_prefixes="moz webkit",
                           boxed=True,
+                          creates_stacking_context=True,
+                          fixpos_cb=True,
                           animatable=True)}
 
 // FIXME: This prop should be animatable
@@ -1819,6 +1826,8 @@ ${helpers.single_keyword("transform-style",
                          "flat preserve-3d",
                          spec="https://drafts.csswg.org/css-transforms/#transform-style-property",
                          extra_prefixes="moz webkit",
+                         creates_stacking_context=True,
+                         fixpos_cb=True,
                          animatable=False)}
 
 <%helpers:longhand name="transform-origin" animatable="True" extra_prefixes="moz webkit" boxed="True"

components/style/properties/longhand/effects.mako.rs

@@ -11,6 +11,7 @@ ${helpers.predefined_type("opacity",
                           "Opacity",
                           "1.0",
                           animatable=True,
+                          creates_stacking_context=True,
                           spec="https://drafts.csswg.org/css-color/#opacity")}
 
 <%helpers:vector_longhand name="box-shadow" allow_empty="True"
@@ -86,6 +87,8 @@ ${helpers.predefined_type("clip",
 
 // FIXME: This prop should be animatable
 <%helpers:longhand name="filter" animatable="False" extra_prefixes="webkit"
+                    creates_stacking_context="True"
+                    fixpos_cb="True"
                    spec="https://drafts.fxtf.org/filters/#propdef-filter">
     //pub use self::computed_value::T as SpecifiedValue;
     use cssparser;
@@ -516,4 +519,5 @@ ${helpers.single_keyword("mix-blend-mode",
                             color-burn hard-light soft-light difference exclusion hue
                             saturation color luminosity""", gecko_constant_prefix="NS_STYLE_BLEND",
                          animatable=False,
+                         creates_stacking_context=True,
                          spec="https://drafts.fxtf.org/compositing/#propdef-mix-blend-mode")}

components/style/properties/longhand/position.mako.rs

@@ -26,6 +26,7 @@
 ${helpers.predefined_type("z-index", "IntegerOrAuto",
                           "Either::Second(Auto)",
                           spec="https://www.w3.org/TR/CSS2/visuren.html#z-index",
+                          creates_stacking_context=True,
                           animatable="True")}
 
 // CSS Flexible Box Layout Module Level 1

components/style/properties/longhand/svg.mako.rs

@@ -59,6 +59,7 @@ ${helpers.single_keyword("mask-type", "luminance alpha",
                          spec="https://drafts.fxtf.org/css-masking/#propdef-mask-type")}
 
 <%helpers:longhand name="clip-path" animatable="False" products="gecko" boxed="True"
+                   creates_stacking_context="True"
                    spec="https://drafts.fxtf.org/css-masking/#propdef-clip-path">
     use std::fmt;
     use style_traits::ToCss;
@@ -189,7 +190,8 @@ ${helpers.single_keyword("mask-composite",
                          spec="https://drafts.fxtf.org/css-masking/#propdef-mask-composite")}
 
 <%helpers:vector_longhand name="mask-image" products="gecko" animatable="False" extra_prefixes="webkit"
-                          has_uncacheable_values="${product == 'gecko'}",
+                          has_uncacheable_values="${product == 'gecko'}"
+                          creates_stacking_context="True"
                           spec="https://drafts.fxtf.org/css-masking/#propdef-mask-image">
     use std::fmt;
     use style_traits::ToCss;

components/style/properties/properties.mako.rs

@@ -420,6 +420,20 @@ impl Parse for CSSWideKeyword {
     }
 }
 
+bitflags! {
+    /// A set of flags for properties.
+    pub flags PropertyFlags: u8 {
+        /// This property requires a stacking context.
+        const CREATES_STACKING_CONTEXT = 0x01,
+        /// This property has values that can establish a containing block for
+        /// fixed positioned and absolutely positioned elements.
+        const FIXPOS_CB = 0x02,
+        /// This property has values that can establish a containing block for
+        /// absolutely positioned elements.
+        const ABSPOS_CB = 0x04,
+    }
+}
+
 /// An identifier for a given longhand property.
 #[derive(Clone, Copy, Eq, PartialEq, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
@@ -458,6 +472,25 @@ impl LonghandId {
             _ => *self
         }
     }
+
+    /// Returns PropertyFlags for given property.
+    pub fn flags(&self) -> PropertyFlags {
+        match *self {
+            % for property in data.longhands:
+                LonghandId::${property.camel_case} =>
+                    %if property.creates_stacking_context:
+                        CREATES_STACKING_CONTEXT |
+                    %endif
+                    %if property.fixpos_cb:
+                        FIXPOS_CB |
+                    %endif
+                    %if property.abspos_cb:
+                        ABSPOS_CB |
+                    %endif
+                    PropertyFlags::empty(),
+            % endfor
+        }
+    }
 }
 
 /// An identifier for a given shorthand property.