fix: drop support for ShadyCSS

src/ConstructStyleSheet.js

@@ -1,7 +1,7 @@
 import {
   constructStyleSheetRegistry,
   deferredStyleSheets,
-  frame, hasShadyCss, shadyCssAdoptersRegistry,
+  frame,
   state,
 } from './shared';
 import {instanceOfStyleSheet} from './utils';
@@ -42,14 +42,6 @@ export function updatePrototype(proto) {
           }
         });
 
-        if (hasShadyCss && shadyCssAdoptersRegistry.has(this)) {
-          const location = shadyCssAdoptersRegistry.get(this);
-
-          // We need to call adoptedStyleSheets setter to re-assign styles
-          // to ShadyCSS.
-          location.adoptedStyleSheets = location.adoptedStyleSheets;
-        }
-
         // And we also need to remember all these changes to apply them to
         // each newly adopted style element.
         actions.push([methodKey, args]);
@@ -66,14 +58,6 @@ function updateAdopters(sheet) {
   adopters.forEach(styleElement => {
     styleElement.innerHTML = basicStyleElement.innerHTML;
   });
-
-  if (hasShadyCss && shadyCssAdoptersRegistry.has(sheet)) {
-    const location = shadyCssAdoptersRegistry.get(sheet);
-
-    // We need to call adoptedStyleSheets setter to re-assign styles
-    // to ShadyCSS.
-    location.adoptedStyleSheets = location.adoptedStyleSheets;
-  }
 }
 
 // This class will be a substitute for the CSSStyleSheet class that

src/init.js

@@ -5,11 +5,9 @@ import {
   adoptedStyleSheetsRegistry,
   deferredStyleSheets,
   frame,
-  hasShadyCss,
-  shadyCssAdoptersRegistry,
   state,
 } from './shared';
-import {checkAndPrepare, reduce} from './utils';
+import {checkAndPrepare} from './utils';
 
 // Initialize the polyfill — Will be called on the window's load event
 export function initPolyfill() {
@@ -84,32 +82,7 @@ export function initAdoptedStyleSheets() {
     adoptedStyleSheetAccessors,
   );
 
-  if (hasShadyCss) {
-    Object.defineProperty(ShadowRoot.prototype, 'adoptedStyleSheets', {
-      configurable: true,
-      get() {
-        return adoptedStyleSheetsRegistry.get(this) || [];
-      },
-      set(sheets) {
-        const uniqueSheets = checkAndPrepare(sheets, this);
-
-        const cssToAdopt = uniqueSheets.map(({cssRules}) =>
-          reduce.call(cssRules, (text, {cssText}) => `${text} ${cssText}`, ''),
-        );
-
-        ShadyCSS.ScopingShim.prepareAdoptedCssText(
-          cssToAdopt,
-          this.host.localName,
-        );
-
-        uniqueSheets.forEach(sheet =>
-          shadyCssAdoptersRegistry.set(sheet, this),
-        );
-
-        ShadyCSS.styleSubtree(this.host);
-      },
-    });
-  } else if (typeof ShadowRoot !== 'undefined') {
+  if (typeof ShadowRoot !== 'undefined') {
     const oldAttachShadow = HTMLElement.prototype.attachShadow;
 
     // Shadow root of each element should be observed to add styles to all

src/shared.js

@@ -1,4 +1,7 @@
-export const hasShadyCss = 'ShadyCSS' in window;
+// Even if the polyfill does not support ShadyCSS, it should be detected in
+// order to avoid errors of parallel usage.
+export const hasShadyCss =
+  'ShadyCSS' in window && !window.ShadyCSS.nativeShadow;
 
 // Style elements that will be attached to the head
 // that need to be moved to the iframe
@@ -21,9 +24,6 @@ export const observerRegistry = new WeakMap();
 // for the specific style element.
 export const appliedActionsCursorRegistry = new WeakMap();
 
-// The list of ShadowRoots for specific sheet (when ShadyCSS is enabled).
-export const shadyCssAdoptersRegistry = new WeakMap();
-
 export const state = {
   // Can we rely on document.body
   loaded: false,

src/utils.js

@@ -29,5 +29,3 @@ export function checkAndPrepare(sheets, location) {
 
   return uniqueSheets;
 }
-
-export const {reduce} = Array.prototype;