style: Standardize different methods to inherit and reset properties.

This avoids special-casing justify-items.

MozReview-Commit-ID: FoEs2IHC1t6
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

components/style/properties/gecko.mako.rs

@@ -398,6 +398,11 @@ impl ${style_struct.gecko_struct_name} {
         self.${on_set}();
         % endif
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
 </%def>
 
 <%def name="impl_coord_copy(ident, gecko_ffi_name)">
@@ -405,6 +410,11 @@ impl ${style_struct.gecko_struct_name} {
     pub fn copy_${ident}_from(&mut self, other: &Self) {
         self.gecko.${gecko_ffi_name}.copy_from(&other.gecko.${gecko_ffi_name});
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
 </%def>
 
 <%!
@@ -482,6 +492,11 @@ def set_gecko_property(ffi_name, expr):
         let color = ${get_gecko_property(gecko_ffi_name, self_param = "other")};
         ${set_gecko_property(gecko_ffi_name, "color")};
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
 </%def>
 
 <%def name="impl_color_clone(ident, gecko_ffi_name)">
@@ -610,6 +625,11 @@ def set_gecko_property(ffi_name, expr):
         }
     }
 
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
+
     #[allow(non_snake_case)]
     pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
         use values::generics::{SVGPaint, SVGPaintKind};
@@ -673,12 +693,20 @@ def set_gecko_property(ffi_name, expr):
         //
         // In practice, this means that we may have an incorrect value here, but
         // we'll adjust that properly in the style fixup phase.
+        //
+        // FIXME(emilio): We could clean this up a bit special-casing the reset_
+        // function below.
         self.gecko.${gecko_ffi_name} = other.gecko.${inherit_from};
         % else:
         self.gecko.${gecko_ffi_name} = other.gecko.${gecko_ffi_name};
         % endif
     }
 
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
+
 %if need_clone:
     #[allow(non_snake_case)]
     pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
@@ -696,6 +724,10 @@ def set_gecko_property(ffi_name, expr):
     pub fn copy_${ident}_from(&mut self, other: &Self) {
         self.gecko.${gecko_ffi_name}.data_at_mut(${index}).copy_from(&other.gecko.${gecko_ffi_name}.data_at(${index}));
     }
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
     % if need_clone:
         #[allow(non_snake_case)]
         pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
@@ -715,6 +747,10 @@ def set_gecko_property(ffi_name, expr):
     pub fn copy_${ident}_from(&mut self, other: &Self) {
         self.gecko.${gecko_ffi_name}.copy_from(&other.gecko.${gecko_ffi_name});
     }
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
     % if need_clone:
         #[allow(non_snake_case)]
         pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
@@ -752,6 +788,11 @@ def set_gecko_property(ffi_name, expr):
         % endfor
         ${ caller.body() }
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
 </%def>
 
 <%def name="impl_corner_style_coord(ident, gecko_ffi_name, x_index, y_index, need_clone)">
@@ -767,6 +808,10 @@ def set_gecko_property(ffi_name, expr):
         self.gecko.${gecko_ffi_name}.data_at_mut(${y_index})
                   .copy_from(&other.gecko.${gecko_ffi_name}.data_at(${y_index}));
     }
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
     % if need_clone:
         #[allow(non_snake_case)]
         pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
@@ -811,6 +856,10 @@ def set_gecko_property(ffi_name, expr):
             self.gecko.${gecko_ffi_name}.set(&other.gecko.${gecko_ffi_name});
         }
     }
+    #[allow(non_snake_case)]
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
     % if need_clone:
         pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
             use values::specified::url::SpecifiedUrl;
@@ -989,6 +1038,10 @@ impl ${style_struct.gecko_struct_name} {
     pub fn copy_${longhand.ident}_from(&mut self, _: &Self) {
         warn!("stylo: Unimplemented property setter: ${longhand.name}");
     }
+    #[allow(non_snake_case)]
+    pub fn reset_${longhand.ident}(&mut self, other: &Self) {
+        self.copy_${longhand.ident}_from(other)
+    }
     % if longhand.need_clone:
     #[allow(non_snake_case)]
     pub fn clone_${longhand.ident}(&self) -> longhands::${longhand.ident}::computed_value::T {
@@ -1164,6 +1217,11 @@ fn static_assert() {
         }
     }
 
+    #[allow(non_snake_case)]
+    pub fn reset__moz_border_${side.ident}_colors(&mut self, other: &Self) {
+        self.copy__moz_border_${side.ident}_colors_from(other)
+    }
+
     #[allow(non_snake_case)]
     pub fn clone__moz_border_${side.ident}_colors(&self)
                                                   -> longhands::_moz_border_${side.ident}_colors::computed_value::T {
@@ -1215,6 +1273,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_border_image_source(&mut self, other: &Self) {
+        self.copy_border_image_source_from(other)
+    }
+
     pub fn clone_border_image_source(&self) -> longhands::border_image_source::computed_value::T {
         use values::None_;
 
@@ -1250,6 +1312,10 @@ fn static_assert() {
         self.gecko.mBorderImageRepeatV = other.gecko.mBorderImageRepeatV;
     }
 
+    pub fn reset_border_image_repeat(&mut self, other: &Self) {
+        self.copy_border_image_repeat_from(other)
+    }
+
     pub fn clone_border_image_repeat(&self) -> longhands::border_image_repeat::computed_value::T {
         use properties::longhands::border_image_repeat::computed_value::RepeatKeyword;
         use gecko_bindings::structs;
@@ -1352,6 +1418,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_z_index(&mut self, other: &Self) {
+        self.copy_z_index_from(other)
+    }
+
     pub fn clone_z_index(&self) -> longhands::z_index::computed_value::T {
         return match self.gecko.mZIndex.as_value() {
             CoordDataValue::Integer(n) => Either::First(n),
@@ -1426,6 +1496,10 @@ fn static_assert() {
         self.gecko.${value.gecko}.mLineName.assign(&*other.gecko.${value.gecko}.mLineName);
     }
 
+    pub fn reset_${value.name}(&mut self, other: &Self) {
+        self.copy_${value.name}_from(other)
+    }
+
     pub fn clone_${value.name}(&self) -> longhands::${value.name}::computed_value::T {
         use gecko_bindings::structs::{nsStyleGridLine_kMinLine, nsStyleGridLine_kMaxLine};
         use string_cache::Atom;
@@ -1464,6 +1538,10 @@ fn static_assert() {
         self.gecko.mGridAuto${kind.title()}Max.copy_from(&other.gecko.mGridAuto${kind.title()}Max);
     }
 
+    pub fn reset_grid_auto_${kind}(&mut self, other: &Self) {
+        self.copy_grid_auto_${kind}_from(other)
+    }
+
     pub fn clone_grid_auto_${kind}(&self) -> longhands::grid_auto_${kind}::computed_value::T {
         ::values::generics::grid::TrackSize::from_gecko_style_coords(&self.gecko.mGridAuto${kind.title()}Min,
                                                                      &self.gecko.mGridAuto${kind.title()}Max)
@@ -1601,6 +1679,10 @@ fn static_assert() {
                                                         &other.gecko.mGridTemplate${kind.title()});
         }
     }
+
+    pub fn reset_grid_template_${kind}(&mut self, other: &Self) {
+        self.copy_grid_template_${kind}_from(other)
+    }
     % endfor
 
     ${impl_simple_type_with_conversion("grid_auto_flow")}
@@ -1640,6 +1722,10 @@ fn static_assert() {
     pub fn copy_grid_template_areas_from(&mut self, other: &Self) {
         unsafe { self.gecko.mGridTemplateAreas.set(&other.gecko.mGridTemplateAreas) }
     }
+
+    pub fn reset_grid_template_areas(&mut self, other: &Self) {
+        self.copy_grid_template_areas_from(other)
+    }
 </%self:impl_trait>
 
 <% skip_outline_longhands = " ".join("outline-style outline-width".split() +
@@ -1674,6 +1760,11 @@ fn static_assert() {
         self.gecko.mOutlineStyle = other.gecko.mOutlineStyle;
     }
 
+    #[allow(non_snake_case)]
+    pub fn reset_outline_style(&mut self, other: &Self) {
+        self.copy_outline_style_from(other)
+    }
+
     #[allow(non_snake_case)]
     pub fn clone_outline_style(&self) -> longhands::outline_style::computed_value::T {
         // FIXME(bholley): Align binary representations and ditch |match| for cast + static_asserts
@@ -1737,7 +1828,7 @@ fn static_assert() {
         };
     }
 
-    pub fn copy_font_feature_settings_from(&mut self, other: &Self ) {
+    pub fn copy_font_feature_settings_from(&mut self, other: &Self) {
         let current_settings = &mut self.gecko.mFont.fontFeatureSettings;
         let feature_settings = &other.gecko.mFont.fontFeatureSettings;
         let settings_length = feature_settings.len() as u32;
@@ -1751,6 +1842,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_font_feature_settings(&mut self, other: &Self) {
+        self.copy_font_feature_settings_from(other)
+    }
+
     pub fn clone_font_feature_settings(&self) -> longhands::font_feature_settings::computed_value::T {
         use values::generics::{FontSettings, FontSettingTag, FontSettingTagInt} ;
 
@@ -1802,6 +1897,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_font_variation_settings(&mut self, other: &Self) {
+        self.copy_font_variation_settings_from(other)
+    }
+
     pub fn fixup_none_generic(&mut self, device: &Device) {
         unsafe {
             bindings::Gecko_nsStyleFont_FixupNoneGeneric(&mut self.gecko, device.pres_context())
@@ -1845,6 +1944,10 @@ fn static_assert() {
         self.gecko.mGenericID = other.gecko.mGenericID;
     }
 
+    pub fn reset_font_family(&mut self, other: &Self) {
+        self.copy_font_family_from(other)
+    }
+
     pub fn clone_font_family(&self) -> longhands::font_family::computed_value::T {
         use properties::longhands::font_family::computed_value::{FontFamily, FamilyName};
         use gecko_bindings::structs::FontFamilyType;
@@ -2082,6 +2185,10 @@ fn static_assert() {
         self.gecko.mFont.sizeAdjust = other.gecko.mFont.sizeAdjust;
     }
 
+    pub fn reset_font_size_adjust(&mut self, other: &Self) {
+        self.copy_font_size_adjust_from(other)
+    }
+
     pub fn clone_font_size_adjust(&self) -> longhands::font_size_adjust::computed_value::T {
         use properties::longhands::font_size_adjust::computed_value::T;
         T::from_gecko_adjust(self.gecko.mFont.sizeAdjust)
@@ -2103,6 +2210,11 @@ fn static_assert() {
         }
     }
 
+    #[allow(non_snake_case)]
+    pub fn reset__x_lang(&mut self, other: &Self) {
+        self.copy__x_lang_from(other)
+    }
+
     <% impl_simple_type_with_conversion("font_language_override", "mFont.languageOverride") %>
 
     pub fn set_font_variant_alternates(&mut self, v: longhands::font_variant_alternates::computed_value::T) {
@@ -2161,6 +2273,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_font_variant_alternates(&mut self, other: &Self) {
+        self.copy_font_variant_alternates_from(other)
+    }
+
     pub fn clone_font_variant_alternates(&self) -> longhands::font_variant_alternates::computed_value::T {
         use Atom;
         % for value in "normal swash stylistic ornaments annotation styleset character_variant historical".split():
@@ -2248,6 +2364,11 @@ fn static_assert() {
             gecko.m${gecko_ffi_name} = other.gecko.m${type.capitalize()}s[index].m${gecko_ffi_name};
         }
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset_${type}_${ident}(&mut self, other: &Self) {
+        self.copy_${type}_${ident}_from(other)
+    }
 </%def>
 
 <%def name="impl_animation_or_transition_count(type, ident, gecko_ffi_name)">
@@ -2437,6 +2558,10 @@ fn static_assert() {
         self.gecko.mOriginalDisplay = other.gecko.mDisplay;
     }
 
+    pub fn reset_display(&mut self, other: &Self) {
+        self.copy_display_from(other)
+    }
+
     <%call expr="impl_keyword_clone('display', 'mDisplay', display_keyword)"></%call>
 
     <% overflow_x = data.longhands_by_name["overflow-x"] %>
@@ -2557,6 +2682,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_scroll_snap_coordinate(&mut self, other: &Self) {
+        self.copy_scroll_snap_coordinate_from(other)
+    }
+
     pub fn clone_scroll_snap_coordinate(&self) -> longhands::scroll_snap_coordinate::computed_value::T {
         let vec = self.gecko.mScrollSnapCoordinate.iter().map(|f| f.into()).collect();
         longhands::scroll_snap_coordinate::computed_value::T(vec)
@@ -2680,6 +2809,10 @@ fn static_assert() {
         unsafe { self.gecko.mSpecifiedTransform.set(&other.gecko.mSpecifiedTransform); }
     }
 
+    pub fn reset_transform(&mut self, other: &Self) {
+        self.copy_transform_from(other)
+    }
+
     <%def name="computed_operation_arm(name, keyword, items)">
         <%
             # %s is substituted with the call to GetArrayItem.
@@ -2869,6 +3002,11 @@ fn static_assert() {
             }
         }
     }
+
+    pub fn reset_transition_property(&mut self, other: &Self) {
+        self.copy_transition_property_from(other)
+    }
+
     ${impl_transition_count('property', 'Property')}
 
     pub fn animations_equals(&self, other: &Self) -> bool {
@@ -2916,6 +3054,11 @@ fn static_assert() {
             animation.mName.assign(&*other.gecko.mAnimations[index].mName);
         }
     }
+
+    pub fn reset_animation_name(&mut self, other: &Self) {
+        self.copy_animation_name_from(other)
+    }
+
     ${impl_animation_count('name', 'Name')}
 
     ${impl_animation_time_value('delay', 'Delay')}
@@ -2979,6 +3122,10 @@ fn static_assert() {
         self.gecko.mPerspectiveOrigin[1].copy_from(&other.gecko.mPerspectiveOrigin[1]);
     }
 
+    pub fn reset_perspective_origin(&mut self, other: &Self) {
+        self.copy_perspective_origin_from(other)
+    }
+
     pub fn clone_perspective_origin(&self) -> longhands::perspective_origin::computed_value::T {
         use properties::longhands::perspective_origin::computed_value::T;
         use values::computed::LengthOrPercentage;
@@ -3002,6 +3149,10 @@ fn static_assert() {
         self.gecko.mTransformOrigin[2].copy_from(&other.gecko.mTransformOrigin[2]);
     }
 
+    pub fn reset_transform_origin(&mut self, other: &Self) {
+        self.copy_transform_origin_from(other)
+    }
+
     pub fn clone_transform_origin(&self) -> longhands::transform_origin::computed_value::T {
         use properties::longhands::transform_origin::computed_value::T;
         use values::computed::LengthOrPercentage;
@@ -3101,6 +3252,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_will_change(&mut self, other: &Self) {
+        self.copy_will_change_from(other)
+    }
+
     pub fn clone_will_change(&self) -> longhands::will_change::computed_value::T {
         use properties::longhands::will_change::computed_value::T;
         use gecko_bindings::structs::nsIAtom;
@@ -3234,6 +3389,10 @@ fn static_assert() {
         }
         self.gecko.${layers_field_name}.${field_name}Count = count;
     }
+
+    pub fn reset_${shorthand}_${name}(&mut self, other: &Self) {
+        self.copy_${shorthand}_${name}_from(other)
+    }
 </%def>
 
 <%def name="impl_simple_image_array_property(name, shorthand, layer_field_name, field_name, struct_name)">
@@ -3384,6 +3543,10 @@ fn static_assert() {
         self.gecko.${image_layers_field}.mPosition${orientation.upper()}Count = count;
     }
 
+    pub fn reset_${shorthand}_position_${orientation}(&mut self, other: &Self) {
+        self.copy_${shorthand}_position_${orientation}_from(other)
+    }
+
     pub fn clone_${shorthand}_position_${orientation}(&self)
         -> longhands::${shorthand}_position_${orientation}::computed_value::T {
         longhands::${shorthand}_position_${orientation}::computed_value::T(
@@ -3495,7 +3658,6 @@ fn static_assert() {
         )
     }
 
-
     pub fn copy_${shorthand}_image_from(&mut self, other: &Self) {
         use gecko_bindings::structs::nsStyleImageLayers_LayerType as LayerType;
         unsafe {
@@ -3515,6 +3677,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_${shorthand}_image(&mut self, other: &Self) {
+        self.copy_${shorthand}_image_from(other)
+    }
+
     #[allow(unused_variables)]
     pub fn set_${shorthand}_image<I>(&mut self, images: I)
         where I: IntoIterator<Item = longhands::${shorthand}_image::computed_value::single_value::T>,
@@ -3630,6 +3796,10 @@ fn static_assert() {
         unsafe { Gecko_CopyListStyleImageFrom(&mut self.gecko, &other.gecko); }
     }
 
+    pub fn reset_list_style_image(&mut self, other: &Self) {
+        self.copy_list_style_image_from(other)
+    }
+
     pub fn clone_list_style_image(&self) -> longhands::list_style_image::computed_value::T {
         use values::specified::url::SpecifiedUrl;
         use values::{Either, None_};
@@ -3667,6 +3837,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_list_style_type(&mut self, other: &Self) {
+        self.copy_list_style_type_from(other)
+    }
+
     pub fn set_quotes(&mut self, other: longhands::quotes::computed_value::T) {
         use gecko_bindings::bindings::Gecko_NewStyleQuoteValues;
         use gecko_bindings::sugar::refptr::UniqueRefPtr;
@@ -3687,6 +3861,10 @@ fn static_assert() {
         unsafe { self.gecko.mQuotes.set(&other.gecko.mQuotes); }
     }
 
+    pub fn reset_quotes(&mut self, other: &Self) {
+        self.copy_quotes_from(other)
+    }
+
     pub fn clone_quotes(&self) -> longhands::quotes::computed_value::T {
         unsafe {
             let ref gecko_quote_values = *self.gecko.mQuotes.mRawPtr;
@@ -3786,6 +3964,10 @@ fn static_assert() {
         self.gecko.mBoxShadow.copy_from(&other.gecko.mBoxShadow);
     }
 
+    pub fn reset_box_shadow(&mut self, other: &Self) {
+        self.copy_box_shadow_from(other)
+    }
+
     pub fn clone_box_shadow(&self) -> longhands::box_shadow::computed_value::T {
         let buf = self.gecko.mBoxShadow.iter().map(|v| v.to_box_shadow()).collect();
         longhands::box_shadow::computed_value::T(buf)
@@ -3846,6 +4028,10 @@ fn static_assert() {
         self.gecko.mClipFlags = other.gecko.mClipFlags;
     }
 
+    pub fn reset_clip(&mut self, other: &Self) {
+        self.copy_clip_from(other)
+    }
+
     pub fn clone_clip(&self) -> longhands::clip::computed_value::T {
         use gecko_bindings::structs::NS_STYLE_CLIP_AUTO;
         use gecko_bindings::structs::NS_STYLE_CLIP_BOTTOM_AUTO;
@@ -3975,6 +4161,10 @@ fn static_assert() {
         }
     }
 
+    pub fn reset_filter(&mut self, other: &Self) {
+        self.copy_filter_from(other)
+    }
+
     pub fn clone_filter(&self) -> longhands::filter::computed_value::T {
         use values::generics::effects::Filter;
         use values::specified::url::SpecifiedUrl;
@@ -4058,6 +4248,10 @@ fn static_assert() {
             bindings::Gecko_CopyImageOrientationFrom(&mut self.gecko, &other.gecko);
         }
     }
+
+    pub fn reset_image_orientation(&mut self, other: &Self) {
+        self.copy_image_orientation_from(other)
+    }
 </%self:impl_trait>
 
 <%self:impl_trait style_struct_name="InheritedTable"
@@ -4073,6 +4267,10 @@ fn static_assert() {
         self.gecko.mBorderSpacingRow = other.gecko.mBorderSpacingRow;
     }
 
+    pub fn reset_border_spacing(&mut self, other: &Self) {
+        self.copy_border_spacing_from(other)
+    }
+
     pub fn clone_border_spacing(&self) -> longhands::border_spacing::computed_value::T {
         longhands::border_spacing::computed_value::T {
             horizontal: Au(self.gecko.mBorderSpacingCol),
@@ -4107,6 +4305,10 @@ fn static_assert() {
         self.gecko.mTextShadow.copy_from(&other.gecko.mTextShadow);
     }
 
+    pub fn reset_text_shadow(&mut self, other: &Self) {
+        self.copy_text_shadow_from(other)
+    }
+
     pub fn clone_text_shadow(&self) -> longhands::text_shadow::computed_value::T {
         let buf = self.gecko.mTextShadow.iter().map(|v| v.to_simple_shadow()).collect();
         longhands::text_shadow::computed_value::T(buf)
@@ -4233,6 +4435,10 @@ fn static_assert() {
         self.gecko.mTextEmphasisStyle = other.gecko.mTextEmphasisStyle;
     }
 
+    pub fn reset_text_emphasis_style(&mut self, other: &Self) {
+        self.copy_text_emphasis_style_from(other)
+    }
+
     pub fn clone_text_emphasis_style(&self) -> longhands::text_emphasis_style::computed_value::T {
         use properties::longhands::text_emphasis_style::computed_value::{T, KeywordValue};
         use properties::longhands::text_emphasis_style::ShapeKeyword;
@@ -4308,6 +4514,7 @@ fn static_assert() {
         clear_if_string(&mut self.gecko.mTextOverflow.mLeft);
         clear_if_string(&mut self.gecko.mTextOverflow.mRight);
     }
+
     pub fn set_text_overflow(&mut self, v: longhands::text_overflow::computed_value::T) {
         use gecko_bindings::structs::nsStyleTextOverflowSide;
         use properties::longhands::text_overflow::Side;
@@ -4345,6 +4552,10 @@ fn static_assert() {
         self.gecko.mTextOverflow.mLogicalDirections = other.gecko.mTextOverflow.mLogicalDirections;
     }
 
+    pub fn reset_text_overflow(&mut self, other: &Self) {
+        self.copy_text_overflow_from(other)
+    }
+
     pub fn clone_text_overflow(&self) -> longhands::text_overflow::computed_value::T {
         use gecko_bindings::structs::nsStyleTextOverflowSide;
         use properties::longhands::text_overflow::Side;
@@ -4388,6 +4599,10 @@ fn static_assert() {
         self.gecko.mInitialLetterSink = other.gecko.mInitialLetterSink;
     }
 
+    pub fn reset_initial_letter(&mut self, other: &Self) {
+        self.copy_initial_letter_from(other)
+    }
+
     pub fn clone_initial_letter(&self) -> longhands::initial_letter::computed_value::T {
         use values::generics::text::InitialLetter;
 
@@ -4525,6 +4740,10 @@ fn static_assert() {
             Gecko_CopyShapeSourceFrom(&mut self.gecko.${gecko_ffi_name}, &other.gecko.${gecko_ffi_name});
         }
     }
+
+    pub fn reset_${ident}(&mut self, other: &Self) {
+        self.copy_${ident}_from(other)
+    }
 </%def>
 
 <% skip_svg_longhands = """
@@ -4592,6 +4811,10 @@ clip-path
         }
     }
 
+    pub fn reset_stroke_dasharray(&mut self, other: &Self) {
+        self.copy_stroke_dasharray_from(other)
+    }
+
     pub fn clone_stroke_dasharray(&self) -> longhands::stroke_dasharray::computed_value::T {
         use values::computed::LengthOrPercentage;
 
@@ -4682,6 +4905,11 @@ clip-path
             bindings::Gecko_nsStyleSVG_CopyContextProperties(&mut self.gecko, &other.gecko);
         }
     }
+
+    #[allow(non_snake_case)]
+    pub fn reset__moz_context_properties(&mut self, other: &Self) {
+        self.copy__moz_context_properties_from(other)
+    }
 </%self:impl_trait>
 
 <%self:impl_trait style_struct_name="Color"
@@ -4785,6 +5013,10 @@ clip-path
         }
     }
 
+    pub fn reset_cursor(&mut self, other: &Self) {
+        self.copy_cursor_from(other)
+    }
+
     pub fn clone_cursor(&self) -> longhands::cursor::computed_value::T {
         use properties::longhands::cursor::computed_value::{Keyword, Image};
         use style_traits::cursor::Cursor;
@@ -5012,6 +5244,10 @@ clip-path
         }
     }
 
+    pub fn reset_content(&mut self, other: &Self) {
+        self.copy_content_from(other)
+    }
+
     % for counter_property in ["Increment", "Reset"]:
         pub fn set_counter_${counter_property.lower()}(&mut self, v: longhands::counter_increment::computed_value::T) {
             unsafe {
@@ -5030,6 +5266,10 @@ clip-path
             }
         }
 
+        pub fn reset_counter_${counter_property.lower()}(&mut self, other: &Self) {
+            self.copy_counter_${counter_property.lower()}_from(other)
+        }
+
         pub fn clone_counter_${counter_property.lower()}(&self) -> longhands::counter_increment::computed_value::T {
             use values::CustomIdent;
             use gecko_string_cache::Atom;

components/style/properties/helpers.mako.rs

@@ -917,6 +917,15 @@
             </%def>
         </%self:logical_setter_helper>
     }
+
+    /// Copy the appropriate physical property from another struct for ${name}
+    /// given a writing mode.
+    pub fn reset_${to_rust_ident(name)}(&mut self,
+                                        other: &Self,
+                                        wm: WritingMode) {
+        self.copy_${to_rust_ident(name)}_from(other, wm)
+    }
+
     % if need_clone:
         /// Get the computed value for the appropriate physical property for
         /// ${name} given a writing mode.

components/style/properties/properties.mako.rs

@@ -1709,6 +1709,13 @@ pub mod style_structs {
                     pub fn copy_${longhand.ident}_from(&mut self, other: &Self) {
                         self.${longhand.ident} = other.${longhand.ident}.clone();
                     }
+
+                    /// Reset ${longhand.name} from the initial struct.
+                    #[allow(non_snake_case)]
+                    #[inline]
+                    pub fn reset_${longhand.ident}(&mut self, other: &Self) {
+                        self.copy_${longhand.ident}_from(other)
+                    }
                     % if longhand.need_clone:
                         /// Get the computed value for ${longhand.name}.
                         #[allow(non_snake_case)]
@@ -2627,19 +2634,14 @@ impl<'a> StyleBuilder<'a> {
     pub fn reset_${property.ident}(&mut self) {
         let reset_struct =
             self.reset_style.get_${property.style_struct.name_lower}();
-        % if property.ident == "justify_items":
+
-            // TODO(emilio): Generalise this!
+        self.${property.style_struct.ident}.mutate()
-            self.${property.style_struct.ident}.mutate()
+            .reset_${property.ident}(
-                .reset_${property.ident}(reset_struct)
+                reset_struct,
-        % else:
+                % if property.logical:
-            self.${property.style_struct.ident}.mutate()
+                self.writing_mode,
-                .copy_${property.ident}_from(
+                % endif
-                    reset_struct,
+            );
-                    % if property.logical:
-                    self.writing_mode,
-                    % endif
-                );
-        % endif
     }
 
     % if not property.is_vector: