Bug 1505489 - Add a pref and enable Shadow Parts in Nightly and for chrome stylesheets. r=heycam

I want to enable in Nightly to evaluate (in the medium term) shipping it without
the part forwarding, once the cascade order and importance issues are fixed, and
that we pass all the tests that don't involve forwarding.

That is, I want to monitor whether having ::part() causes compat issues or not.

Depends on D32648

Differential Revision: https://phabricator.services.mozilla.com/D32649

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.h

@@ -4721,6 +4721,19 @@ VARCACHE_PREF(
   bool, false
 )
 
+#ifdef NIGHTLY_BUILD
+# define PREF_VALUE true
+#else
+# define PREF_VALUE false
+#endif
+VARCACHE_PREF(
+  Live,
+  "layout.css.shadow-parts.enabled",
+   layout_css_shadow_parts_enabled,
+  bool, PREF_VALUE
+)
+#undef PREF_VALUE
+
 #ifdef NIGHTLY_BUILD
 # define PREF_VALUE true
 #else

servo/components/style/gecko/selector_parser.rs

@@ -5,7 +5,7 @@
 //! Gecko-specific bits for selector-parsing.
 
 use crate::element_state::{DocumentState, ElementState};
-use crate::gecko_bindings::structs::RawServoSelectorList;
+use crate::gecko_bindings::structs::{self, RawServoSelectorList};
 use crate::gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
 use crate::invalidation::element::document_state::InvalidationMatchingData;
 use crate::selector_parser::{Direction, SelectorParser};
@@ -349,7 +349,14 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
 
     #[inline]
     fn parse_host(&self) -> bool {
-        self.parse_slotted()
+        true
+    }
+
+    #[inline]
+    fn parse_part(&self) -> bool {
+        self.chrome_rules_enabled() || unsafe {
+            structs::StaticPrefs_sVarCache_layout_css_shadow_parts_enabled
+        }
     }
 
     fn parse_non_ts_pseudo_class(

testing/web-platform/meta/css/css-shadow-parts/__dir__.ini

@@ -0,0 +1 @@
+prefs: [layout.css.shadow-parts.enabled:true]

testing/web-platform/meta/css/css-shadow-parts/all-hosts.html.ini

@@ -1,6 +0,0 @@
-[all-hosts.html]
-  [::part with host selector styles in first host]
-    expected: FAIL
-
-  [::part with host selector styles in second host]
-    expected: FAIL

testing/web-platform/meta/css/css-shadow-parts/chaining-invalid-selector.html.ini

@@ -1,4 +0,0 @@
-[chaining-invalid-selector.html]
-  [CSS Shadow Parts - Chaining Invalid Selector]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/complex-matching.html.ini

@@ -1,4 +0,0 @@
-[complex-matching.html]
-  [Complex selector for host works]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/complex-non-matching.html.ini

@@ -1,4 +0,0 @@
-[complex-non-matching.html]
-  [CSS Shadow Parts - Complex Non-matching]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/different-host.html.ini

@@ -1,4 +0,0 @@
-[different-host.html]
-  [CSS Shadow Parts - Different Host]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/inner-host.html.ini

@@ -1,4 +0,0 @@
-[inner-host.html]
-  [Part in outer host is styled by document style sheet]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/interaction-with-placeholder.html.ini

@@ -1,2 +0,0 @@
-[interaction-with-placeholder.html]
-  expected: FAIL

testing/web-platform/meta/css/css-shadow-parts/interaction-with-pseudo-elements.html.ini

@@ -1,19 +0,0 @@
-[interaction-with-pseudo-elements.html]
-  [::first-letter in selected host is styled]
-    expected: FAIL
-
-  [::first-line in selected host is styled]
-    expected: FAIL
-
-  [::before in selected host is styled]
-    expected: FAIL
-
-  [::placeholder in selected host is styled]
-    expected: FAIL
-
-  [::selection in selected host is styled]
-    expected: FAIL
-
-  [::after in selected host is styled]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/invalidation-change-part-name.html.ini

@@ -1,4 +0,0 @@
-[invalidation-change-part-name.html]
-  [Part in selected host changed color]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/invalidation-complex-selector.html.ini

@@ -1,4 +0,0 @@
-[invalidation-complex-selector.html]
-  [Part in selected host changed color]
-    expected: FAIL
-

testing/web-platform/meta/css/css-shadow-parts/simple.html.ini

@@ -1,4 +0,0 @@
-[simple.html]
-  [Part in selected host is styled]
-    expected: FAIL
-