fix(compiler): support one additional level of nesting in :host()

mattrbeck · thePunderWoman · commit 444143758e05 · 2025-11-06T10:53:42.000-08:00
Previously we supported one level of nested parentheses inside of a `:host()` selector, e.g. `:host(:not(p))`. This caused a breakage in g3 when I migrated a selector from `:host:not(:has(p))` to `:host(:not(:has(p)))`. This change adds support for just one more level of nesting. It'd be nice to move everything to a real CSS parser (or even update it to count parentheses like I did with :host-context()), but I wasn't able to get that to work in ~20 minutes and I'm focusing on other things at the moment. This change punts the problem until somebody tries to use just one more level of nesting in a selector. Fixes #64830
diff --git a/packages/compiler/src/shadow_css.ts b/packages/compiler/src/shadow_css.ts
@@ -1067,7 +1067,13 @@ const _cssContentUnscopedRuleRe =
 const _polyfillHost = '-shadowcsshost';
 // note: :host-context pre-processed to -shadowcsshostcontext.
 const _polyfillHostContext = '-shadowcsscontext';
-const _parenSuffix = '(?:\\((' + '(?:\\([^)(]*\\)|[^)(]*)+?' + ')\\))';
+// Matches text content with no parentheses, e.g., "foo"
+const _noParens = '[^)(]*';
+// Matches content with at most ONE level of nesting, e.g., "a(b)c"
+const _level1Parens = String.raw`(?:\(${_noParens}\)|${_noParens})+?`;
+// Matches content with at most TWO levels of nesting, e.g., "a(b(c)d)e"
+const _level2Parens = String.raw`(?:\(${_level1Parens}\)|${_noParens})+?`;
+const _parenSuffix = String.raw`(?:\((${_level2Parens})\))`;
 const _cssColonHostRe = new RegExp(_polyfillHost + _parenSuffix + '?([^,{]*)', 'gim');
 // note: :host-context patterns are terminated with `{`, as opposed to :host which
 // is both `{` and `,` because :host-context handles top-level commas differently.
diff --git a/packages/compiler/test/shadow_css/host_and_host_context_spec.ts b/packages/compiler/test/shadow_css/host_and_host_context_spec.ts
@@ -83,6 +83,9 @@ describe('ShadowCss, :host and :host-context', () => {
       expect(shim(':host(:not(p)):before {}', 'contenta', 'a-host')).toEqualCss(
         '[a-host]:not(p):before {}',
       );
+      expect(shim(':host(:not(:has(p))) {}', 'contenta', 'a-host')).toEqualCss(
+        '[a-host]:not(:has(p)) {}',
+      );
       expect(shim(':host:not(:host.foo) {}', 'contenta', 'a-host')).toEqualCss(
         '[a-host]:not([a-host].foo) {}',
       );
