fix(compiler): incorrectly encapsulating selectors with escape sequences (#40264)

CSS supports escaping in selectors, e.g. writing `.foo:bar` will match an element with the
`foo` class and `bar` pseudo-class, but `.foo\:bar` will match the `foo:bar` class. Our
shimmed shadow DOM encapsulation always assumes that `:` means a pseudo selector
which breaks a selector like `.foo\:bar`.

These changes add some extra logic so that escaped characters in selectors are preserved.

Fixes #31844.

PR Close #40264

packages/compiler/src/shadow_css.ts

@@ -485,12 +485,14 @@ class SafeSelector {
   constructor(selector: string) {
     // Replaces attribute selectors with placeholders.
     // The WS in [attr="va lue"] would otherwise be interpreted as a selector separator.
-    selector = selector.replace(/(\[[^\]]*\])/g, (_, keep) => {
-      const replaceBy = `__ph-${this.index}__`;
-      this.placeholders.push(keep);
-      this.index++;
-      return replaceBy;
-    });
+    selector = this._escapeRegexMatches(selector, /(\[[^\]]*\])/g);
+
+    // CSS allows for certain special characters to be used in selectors if they're escaped.
+    // E.g. `.foo:blue` won't match a class called `foo:blue`, because the colon denotes a
+    // pseudo-class, but writing `.foo\:blue` will match, because the colon was escaped.
+    // Replace all escape sequences (`\` followed by a character) with a placeholder so
+    // that our handling of pseudo-selectors doesn't mess with them.
+    selector = this._escapeRegexMatches(selector, /(\\.)/g);
 
     // Replaces the expression in `:nth-child(2n + 1)` with a placeholder.
     // WS and "+" would otherwise be interpreted as selector separators.
@@ -503,12 +505,25 @@ class SafeSelector {
   }
 
   restore(content: string): string {
-    return content.replace(/__ph-(\d+)__/g, (ph, index) => this.placeholders[+index]);
+    return content.replace(/__ph-(\d+)__/g, (_ph, index) => this.placeholders[+index]);
   }
 
   content(): string {
     return this._content;
   }
+
+  /**
+   * Replaces all of the substrings that match a regex within a
+   * special string (e.g. `__ph-0__`, `__ph-1__`, etc).
+   */
+  private _escapeRegexMatches(content: string, pattern: RegExp): string {
+    return content.replace(pattern, (_, keep) => {
+      const replaceBy = `__ph-${this.index}__`;
+      this.placeholders.push(keep);
+      this.index++;
+      return replaceBy;
+    });
+  }
 }
 
 const _cssContentNextSelectorRe =

packages/compiler/test/shadow_css_spec.ts

@@ -10,7 +10,7 @@ import {CssRule, processRules, ShadowCss} from '@angular/compiler/src/shadow_css
 import {normalizeCSS} from '@angular/platform-browser/testing/src/browser_util';
 
 {
-  describe('ShadowCss', function() {
+  describe('ShadowCss', () => {
     function s(css: string, contentAttr: string, hostAttr: string = '') {
       const shadowCss = new ShadowCss();
       const shim = shadowCss.shimCssText(css, contentAttr, hostAttr);
@@ -112,6 +112,15 @@ import {normalizeCSS} from '@angular/platform-browser/testing/src/browser_util';
       expect(s('[is="one"] {}', 'contenta')).toEqual('[is="one"][contenta] {}');
     });
 
+    it('should handle escaped sequences in selectors', () => {
+      expect(s('one\\/two {}', 'contenta')).toEqual('one\\/two[contenta] {}');
+      expect(s('one\\:two {}', 'contenta')).toEqual('one\\:two[contenta] {}');
+      expect(s('one\\\\:two {}', 'contenta')).toEqual('one\\\\[contenta]:two {}');
+      expect(s('.one\\:two {}', 'contenta')).toEqual('.one\\:two[contenta] {}');
+      expect(s('.one\\:two .three\\:four {}', 'contenta'))
+          .toEqual('.one\\:two[contenta] .three\\:four[contenta] {}');
+    });
+
     describe((':host'), () => {
       it('should handle no context', () => {
         expect(s(':host {}', 'contenta', 'a-host')).toEqual('[a-host] {}');