From ad421513ea6ac033ea657c91649eab4b09a19b2f Mon Sep 17 00:00:00 2001
From: Martin Hristov <martin.r.hristov@gmail.com>
Date: Thu, 18 Apr 2019 11:40:42 +0300
Subject: [PATCH] fix(postcss-merge-rules): prevent merging of :host(tag) and
 tag

Fixes: https://github.com/cssnano/cssnano/issues/730
---
 .all-contributorsrc                                 | 12 +++++++++++-
 CONTRIBUTORS.md                                     |  3 +++
 packages/postcss-merge-rules/src/__tests__/index.js |  8 ++++++++
 packages/postcss-merge-rules/src/index.js           |  5 +++++
 4 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/.all-contributorsrc b/.all-contributorsrc
index 18600c6fc..6d8513f29 100644
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@@ -620,7 +620,17 @@
       "contributions": [
         "maintenance"
       ]
+    },
+    {
+      "login": "MapTo0",
+      "name": "Martin",
+      "avatar_url": "https://avatars.githubusercontent.com/u/5821279?v=4",
+      "profile": "https://github.com/MapTo0",
+      "contributions": [
+        "code"
+      ]
     }
   ],
-  "repoType": "github"
+  "repoType": "github",
+  "commitConvention": "none"
 }
diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index f842e9a63..f708b8c39 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -87,6 +87,9 @@ Thanks goes to these wonderful people ([emoji key](https://github.com/kentcdodds
     <td align="center"><a href="https://genemecija.com"><img src="https://avatars2.githubusercontent.com/u/39816902?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Gene Mecija</b></sub></a><br /><a href="https://github.com/cssnano/cssnano/issues?q=author%3Agenemecija" title="Bug reports">🐛</a> <a href="https://github.com/cssnano/cssnano/commits?author=genemecija" title="Code">💻</a> <a href="https://github.com/cssnano/cssnano/commits?author=genemecija" title="Tests">⚠️</a></td>
     <td align="center"><a href="https://www.ludofischer.com"><img src="https://avatars1.githubusercontent.com/u/43557?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ludovico Fischer</b></sub></a><br /><a href="#maintenance-ludofischer" title="Maintenance">🚧</a></td>
   </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/MapTo0"><img src="https://avatars.githubusercontent.com/u/5821279?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Martin</b></sub></a><br /><a href="https://github.com/cssnano/cssnano/commits?author=MapTo0" title="Code">💻</a></td>
+  </tr>
 </table>
 
 <!-- markdownlint-restore -->
diff --git a/packages/postcss-merge-rules/src/__tests__/index.js b/packages/postcss-merge-rules/src/__tests__/index.js
index 505654015..43ed8e5a7 100644
--- a/packages/postcss-merge-rules/src/__tests__/index.js
+++ b/packages/postcss-merge-rules/src/__tests__/index.js
@@ -619,6 +619,14 @@ test('should not crash when node.raws.value is null (2)', () => {
   );
 });
 
+test(
+  'should not merge :host(tagname) with tagname',
+  processCSS(
+    ':host(tag){display:block}tag{display:block}',
+    ':host(tag){display:block}tag{display:block}'
+  )
+);
+
 test(
   'should merge multiple media queries',
   processCSS(
diff --git a/packages/postcss-merge-rules/src/index.js b/packages/postcss-merge-rules/src/index.js
index eda11f530..ce1e8b915 100644
--- a/packages/postcss-merge-rules/src/index.js
+++ b/packages/postcss-merge-rules/src/index.js
@@ -94,6 +94,11 @@ 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;