Backed out changeset 5197801f499d (bug 1848639) for causing multiple build bustages related to "zoom". CLOSED TREE

layout/reftests/transform/reftest.list

@@ -152,6 +152,10 @@ fails == translate-rounding-3.html translate-rounding-viewport-ref.html # bug 13
 pref(layout.css.individual-transform.enabled,true) == animate-layer-scale-inherit-4.html animate-layer-scale-inherit-4-ref.html
 fuzzy-if(winWidget,0-1,0-1000) == 1569215-1.html 1569215-1-ref.html
 
+test-pref(layout.css.zoom-transform-hack.enabled,true) == zoom-hack-1.html zoom-hack-ref.html
+test-pref(layout.css.zoom-transform-hack.enabled,false) != zoom-hack-1.html zoom-hack-ref.html
+test-pref(layout.css.zoom-transform-hack.enabled,true) == zoom-hack-2.html zoom-hack-ref.html
+
 == transform-anon-block-1.html transform-anon-block-1-ref.html
 test-pref(layout.animation.prerender.partial.jank,true) test-pref(layout.animation.prerender.partial,true) == partial-prerender-expansion-translate.html partial-prerender-expansion-ref.html
 test-pref(layout.animation.prerender.partial,true) == partial-prerender-translate-1.html about:blank

layout/reftests/transform/zoom-hack-1.html

@@ -0,0 +1,10 @@
+<!doctype html>
+<style>
+  div {
+    width: 100px;
+    height: 100px;
+    background: green;
+    zoom: 2;
+  }
+</style>
+<div></div>

layout/reftests/transform/zoom-hack-2.html

@@ -0,0 +1,10 @@
+<!doctype html>
+<style>
+  div {
+    width: 200px;
+    height: 200px;
+    background: green;
+    zoom: 0;
+  }
+</style>
+<div></div>

layout/reftests/transform/zoom-hack-ref.html

@@ -0,0 +1,9 @@
+<!doctype html>
+<style>
+  div {
+    width: 200px;
+    height: 200px;
+    background: green;
+  }
+</style>
+<div></div>

layout/style/test/property_database.js

@@ -13674,6 +13674,18 @@ if (IsCSSPropertyPrefEnabled("layout.css.backdrop-filter.enabled")) {
   };
 }
 
+if (IsCSSPropertyPrefEnabled("layout.css.zoom-transform-hack.enabled")) {
+  gCSSProperties["zoom"] = {
+    domProp: "zoom",
+    inherited: false,
+    type: CSS_TYPE_LEGACY_SHORTHAND,
+    subproperties: ["transform", "transform-origin"],
+    initial_values: ["normal", "1.0", "0", "0%", "100%"],
+    other_values: ["10%", "2", "2.5"],
+    invalid_values: ["0 0", "foo", "10px"],
+  };
+}
+
 if (IsCSSPropertyPrefEnabled("layout.css.math-depth.enabled")) {
   gCSSProperties["math-depth"] = {
     domProp: "mathDepth",

modules/libpref/init/StaticPrefList.yaml

@@ -8184,6 +8184,13 @@
   value: true
   mirror: always
 
+# Make `zoom` a `transform` + `transform-origin` alias.
+- name: layout.css.zoom-transform-hack.enabled
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+  rust: true
+
 # Whether the `-moz-control-character-visibility` property is exposed to
 # content.
 #

servo/components/style/properties/shorthands/box.mako.rs

@@ -252,3 +252,60 @@ ${helpers.two_properties_shorthand(
         }
     }
 </%helpers:shorthand>
+
+<%helpers:shorthand name="zoom" engines="gecko"
+                    sub_properties="transform transform-origin"
+                    gecko_pref="layout.css.zoom-transform-hack.enabled"
+                    flags="SHORTHAND_IN_GETCS IS_LEGACY_SHORTHAND"
+                    spec="Not a standard, only a compat hack">
+    use crate::parser::Parse;
+    use crate::values::specified::{Number, NumberOrPercentage, TransformOrigin};
+    use crate::values::generics::transform::{Transform, TransformOperation};
+
+    pub fn parse_value<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Longhands, ParseError<'i>> {
+        let zoom = match input.try_parse(|input| NumberOrPercentage::parse(context, input)) {
+            Ok(number_or_percent) => number_or_percent.to_number(),
+            Err(..) => {
+                input.expect_ident_matching("normal")?;
+                Number::new(1.0)
+            },
+        };
+
+        // Make sure that the initial value matches the values for the
+        // longhands, just for general sanity.  `zoom: 1` and `zoom: 0` are
+        // ignored, see [1][2]. They are just hack for the "has layout" mode on
+        // IE.
+        //
+        // [1]: https://bugs.webkit.org/show_bug.cgi?id=18467
+        // [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1593009
+        Ok(if zoom.get() == 1.0 || zoom.get() == 0.0 {
+            expanded! {
+                transform: Transform::none(),
+                transform_origin: TransformOrigin::initial_value(),
+            }
+        } else {
+            expanded! {
+                transform: Transform(vec![TransformOperation::Scale(zoom, zoom)].into()),
+                transform_origin: TransformOrigin::zero_zero(),
+            }
+        })
+    }
+
+    impl<'a> ToCss for LonghandsToSerialize<'a>  {
+        fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result where W: fmt::Write {
+            if self.transform.0.is_empty() && *self.transform_origin == TransformOrigin::initial_value() {
+                return 1.0f32.to_css(dest);
+            }
+            if *self.transform_origin != TransformOrigin::zero_zero() {
+                return Ok(())
+            }
+            match &*self.transform.0 {
+                [TransformOperation::Scale(x, y)] if x == y => x.to_css(dest),
+                _ => Ok(()),
+            }
+        }
+    }
+</%helpers:shorthand>