Bug 1843527 - Move abs() function behind a pref. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D183574

modules/libpref/init/StaticPrefList.yaml

@@ -8235,6 +8235,13 @@
   mirror: always
   rust: true
 
+# Whether sign/abs functions are enabled in calc().
+- name: layout.css.abs-sign.enabled
+  type: RelaxedAtomicBool
+  value: @IS_NIGHTLY_BUILD@
+  mirror: always
+  rust: true
+
 # Whether infinity / nan constants are enabled in calc().
 - name: layout.css.nan-inf.enabled
   type: RelaxedAtomicBool

servo/components/style/values/specified/calc.rs

@@ -968,6 +968,8 @@ impl CalcNode {
             static_prefs::pref!("layout.css.mod-rem.enabled")
         } else if matches!(function, Pow | Sqrt | Hypot | Log | Exp) {
             static_prefs::pref!("layout.css.exp.enabled")
+        } else if matches!(function, Abs) {
+            static_prefs::pref!("layout.css.abs-sign.enabled")
         } else {
             true
         };