feat(cdk-scrollable): add methods to normalize scrolling in RTL (#12607)

* feat(cdk-scrollable): add methods to normalize scrolling in RTL

* address comments

Author: mmalerba

src/cdk/platform/features.ts renamed to src/cdk/platform/features/input-types.ts

@@ -6,33 +6,6 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-/** Cached result of whether the user's browser supports passive event listeners. */
-let supportsPassiveEvents: boolean;
-
-/**
- * Checks whether the user's browser supports passive event listeners.
- * See: https://github.com/WICG/EventListenerOptions/blob/gh-pages/explainer.md
- */
-export function supportsPassiveEventListeners(): boolean {
-  if (supportsPassiveEvents == null && typeof window !== 'undefined') {
-    try {
-      window.addEventListener('test', null!, Object.defineProperty({}, 'passive', {
-        get: () => supportsPassiveEvents = true
-      }));
-    } finally {
-      supportsPassiveEvents = supportsPassiveEvents || false;
-    }
-  }
-
-  return supportsPassiveEvents;
-}
-
-/** Check whether the browser supports scroll behaviors. */
-export function supportsScrollBehavior(): boolean {
-  return !!(document && document.documentElement && document.documentElement.style &&
-      'scrollBehavior' in document.documentElement.style);
-}
-
 /** Cached result Set of input types support by the current browser. */
 let supportedInputTypes: Set<string>;
 

src/cdk/platform/features/passive-listeners.ts

@@ -0,0 +1,28 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/** Cached result of whether the user's browser supports passive event listeners. */
+let supportsPassiveEvents: boolean;
+
+/**
+ * Checks whether the user's browser supports passive event listeners.
+ * See: https://github.com/WICG/EventListenerOptions/blob/gh-pages/explainer.md
+ */
+export function supportsPassiveEventListeners(): boolean {
+  if (supportsPassiveEvents == null && typeof window !== 'undefined') {
+    try {
+      window.addEventListener('test', null!, Object.defineProperty({}, 'passive', {
+        get: () => supportsPassiveEvents = true
+      }));
+    } finally {
+      supportsPassiveEvents = supportsPassiveEvents || false;
+    }
+  }
+
+  return supportsPassiveEvents;
+}

src/cdk/platform/features/scrolling.ts

@@ -0,0 +1,84 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/** The possible ways the browser may handle the horizontal scroll axis in RTL languages. */
+export enum RtlScrollAxisType {
+  /**
+   * scrollLeft is 0 when scrolled all the way left and (scrollWidth - clientWidth) when scrolled
+   * all the way right.
+   */
+  NORMAL,
+  /**
+   * scrollLeft is -(scrollWidth - clientWidth) when scrolled all the way left and 0 when scrolled
+   * all the way right.
+   */
+  NEGATED,
+  /**
+   * scrollLeft is (scrollWidth - clientWidth) when scrolled all the way left and 0 when scrolled
+   * all the way right.
+   */
+  INVERTED
+}
+
+/** Cached result of the way the browser handles the horizontal scroll axis in RTL mode. */
+let rtlScrollAxisType: RtlScrollAxisType;
+
+/** Check whether the browser supports scroll behaviors. */
+export function supportsScrollBehavior(): boolean {
+  return !!(typeof document == 'object' && 'scrollBehavior' in document.documentElement.style);
+}
+
+/**
+ * Checks the type of RTL scroll axis used by this browser. As of time of writing, Chrome is NORMAL,
+ * Firefox & Safari are NEGATED, and IE & Edge are INVERTED.
+ */
+export function getRtlScrollAxisType(): RtlScrollAxisType {
+  // We can't check unless we're on the browser. Just assume 'normal' if we're not.
+  if (typeof document !== 'object' || !document) {
+    return RtlScrollAxisType.NORMAL;
+  }
+
+  if (!rtlScrollAxisType) {
+    // Create a 1px wide scrolling container and a 2px wide content element.
+    const scrollContainer = document.createElement('div');
+    const containerStyle = scrollContainer.style;
+    scrollContainer.dir = 'rtl';
+    containerStyle.height = '1px';
+    containerStyle.width = '1px';
+    containerStyle.overflow = 'auto';
+    containerStyle.visibility = 'hidden';
+    containerStyle.pointerEvents = 'none';
+    containerStyle.position = 'absolute';
+
+    const content = document.createElement('div');
+    const contentStyle = content.style;
+    contentStyle.width = '2px';
+    contentStyle.height = '1px';
+
+    scrollContainer.appendChild(content);
+    document.body.appendChild(scrollContainer);
+
+    rtlScrollAxisType = RtlScrollAxisType.NORMAL;
+
+    // The viewport starts scrolled all the way to the right in RTL mode. If we are in a NORMAL
+    // browser this would mean that the scrollLeft should be 1. If it's zero instead we know we're
+    // dealing with one of the other two types of browsers.
+    if (scrollContainer.scrollLeft === 0) {
+      // In a NEGATED browser the scrollLeft is always somewhere in [-maxScrollAmount, 0]. For an
+      // INVERTED browser it is always somewhere in [0, maxScrollAmount]. We can determine which by
+      // setting to the scrollLeft to 1. This is past the max for a NEGATED browser, so it will
+      // return 0 when we read it again.
+      scrollContainer.scrollLeft = 1;
+      rtlScrollAxisType =
+          scrollContainer.scrollLeft === 0 ? RtlScrollAxisType.NEGATED : RtlScrollAxisType.INVERTED;
+    }
+
+    scrollContainer.parentNode!.removeChild(scrollContainer);
+  }
+  return rtlScrollAxisType;
+}

src/cdk/platform/public-api.ts

@@ -7,5 +7,7 @@
  */
 
 export * from './platform';
-export * from './features';
 export * from './platform-module';
+export * from './features/input-types';
+export * from './features/passive-listeners';
+export * from './features/scrolling';

src/cdk/scrolling/BUILD.bazel

@@ -10,6 +10,7 @@ ng_module(
   module_name = "@angular/cdk/scrolling",
   assets = [":virtual-scroll-viewport.css"] + glob(["**/*.html"]),
   deps = [
+    "//src/cdk/bidi",
     "//src/cdk/coercion",
     "//src/cdk/collections",
     "//src/cdk/platform",
@@ -29,6 +30,7 @@ ts_library(
   srcs = glob(["**/*.spec.ts"]),
   deps = [
     ":scrolling",
+    "//src/cdk/bidi",
     "//src/cdk/collections",
     "//src/cdk/testing",
     "@rxjs",