From 70091c6bcf8767a4894447d909c59d53e4dad7c2 Mon Sep 17 00:00:00 2001
From: Ludovico Fischer <livrerie@gmail.com>
Date: Tue, 11 May 2021 23:09:40 +0200
Subject: [PATCH] chore(postcss-merge-rules): refactor Move all checks
 together.

---
 packages/postcss-merge-rules/src/index.js                | 5 -----
 .../postcss-merge-rules/src/lib/ensureCompatibility.js   | 9 +++++++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/packages/postcss-merge-rules/src/index.js b/packages/postcss-merge-rules/src/index.js
index ce1e8b915..eda11f530 100644
--- a/packages/postcss-merge-rules/src/index.js
+++ b/packages/postcss-merge-rules/src/index.js
@@ -94,11 +94,6 @@ function canMerge(ruleA, ruleB, browsers, compatibilityCache) {
   const b = ruleB.selectors;
 
   const selectors = a.concat(b);
-  const hasHost = selectors.some((selector) => selector.includes(':host'));
-
-  if (hasHost) {
-    return false;
-  }
 
   if (!ensureCompatibility(selectors, browsers, compatibilityCache)) {
     return false;
diff --git a/packages/postcss-merge-rules/src/lib/ensureCompatibility.js b/packages/postcss-merge-rules/src/lib/ensureCompatibility.js
index 1e52f82de..68e855d4c 100644
--- a/packages/postcss-merge-rules/src/lib/ensureCompatibility.js
+++ b/packages/postcss-merge-rules/src/lib/ensureCompatibility.js
@@ -61,6 +61,10 @@ function isCssMixin(selector) {
   return selector[selector.length - 1] === ':';
 }
 
+function isHostPseudoClass(selector) {
+  return selector.includes(':host');
+}
+
 const isSupportedCache = {};
 
 // Move to util in future
@@ -85,6 +89,11 @@ export default function ensureCompatibility(
   if (selectors.some(isCssMixin)) {
     return false;
   }
+
+  // Should not merge :host selector https://github.com/angular/angular-cli/issues/18672
+  if (selectors.some(isHostPseudoClass)) {
+    return false;
+  }
   return selectors.every((selector) => {
     if (simpleSelectorRe.test(selector)) {
       return true;