fix(compiler): apply style on :host attribudes in prod builds.

In prod builds, selectors are optimized and spaces a removed. angular#48558 introduced a regression on selectors without spaces. This commit fixes tihs.

Fixes angular#49100

packages/compiler/src/shadow_css.ts

@@ -696,7 +696,7 @@ export class ShadowCss {
       // (ie: ".\fc ber" for ".über") is not a separator between 2 selectors
       // also keep in mind that backslashes are replaced by a placeholder by SafeSelector
       // These escaped selectors happen for example when esbuild runs with optimization.minify.
-      if (part.match(_placeholderRe) && selector[res.index + 1]?.match(/[a-fA-F\d]/)) {
+      if (part.match(/__esc-ph-(\d+)__/g) && selector[res.index + 1]?.match(/[a-fA-F\d]/)) {
         continue;
       }
 
@@ -735,7 +735,13 @@ class SafeSelector {
     // 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);
+    // Escaped characters have a specific placeholder so they can be detected separately.
+    selector = selector.replace(/(\\.)/g, (_, keep) => {
+      const replaceBy = `__esc-ph-${this.index}__`;
+      this.placeholders.push(keep);
+      this.index++;
+      return replaceBy;
+    });
 
     // Replaces the expression in `:nth-child(2n + 1)` with a placeholder.
     // WS and "+" would otherwise be interpreted as selector separators.
@@ -748,7 +754,7 @@ class SafeSelector {
   }
 
   restore(content: string): string {
-    return content.replace(_placeholderRe, (_ph, index) => this.placeholders[+index]);
+    return content.replace(/__(?:ph|esc-ph)-(\d+)__/g, (_ph, index) => this.placeholders[+index]);
   }
 
   content(): string {
@@ -804,8 +810,6 @@ const _colonHostContextRe = /:host-context/gim;
 
 const _commentRe = /\/\*[\s\S]*?\*\//g;
 
-const _placeholderRe = /__ph-(\d+)__/g;
-
 function stripComments(input: string): string {
   return input.replace(_commentRe, '');
 }

packages/compiler/test/shadow_css/host_and_host_context_spec.ts

@@ -27,6 +27,11 @@ describe('ShadowCss, :host and :host-context', () => {
       expect(shim(':host([a=b]) {}', 'contenta', 'a-host')).toEqualCss('[a=b][a-host] {}');
     });
 
+    it('should handle attribute and next operator without spaces', () => {
+      expect(shim(':host[foo]>div {}', 'contenta', 'a-host'))
+          .toEqualCss(('[foo][a-host] > div[contenta] {}'));
+    });
+
     it('should handle multiple tag selectors', () => {
       expect(shim(':host(ul,li) {}', 'contenta', 'a-host')).toEqualCss('ul[a-host], li[a-host] {}');
       expect(shim(':host(ul,li) > .z {}', 'contenta', 'a-host'))