From 7ed24db8e239f8535969fde2bb780805dcf7f84a Mon Sep 17 00:00:00 2001
From: Konv Suu <hi@kovsu.com>
Date: Fri, 11 Sep 2026 16:09:34 +0800
Subject: [PATCH] Handlebars: Stop formatting `<style lang="">` as CSS (#20031)

Co-authored-by: fisker <lionkay@gmail.com>
---
 changelog_unreleased/handlebars/20031.md      | 23 +++++++
 src/language-handlebars/embed.js              |  3 +-
 .../__snapshots__/format.test.js.snap         | 65 ++++++++++---------
 .../style-tag/with-lang-attribute-2.hbs       | 10 ---
 .../style-tag/with-lang-attribute-3.hbs       |  9 ---
 .../style-tag/with-lang-attribute.hbs         | 32 +++++++++
 6 files changed, 89 insertions(+), 53 deletions(-)
 create mode 100644 changelog_unreleased/handlebars/20031.md
 delete mode 100644 tests/format/handlebars/style-tag/with-lang-attribute-2.hbs
 delete mode 100644 tests/format/handlebars/style-tag/with-lang-attribute-3.hbs

diff --git a/changelog_unreleased/handlebars/20031.md b/changelog_unreleased/handlebars/20031.md
new file mode 100644
index 000000000..a3718bde3
--- /dev/null
+++ b/changelog_unreleased/handlebars/20031.md
@@ -0,0 +1,23 @@
+#### Don't format `<style lang="">` as CSS (#20031 by @kovsu)
+
+<!-- prettier-ignore -->
+```hbs
+{{! Input }}
+<style lang="">
+  .a { color: red;
+  }
+</style>
+
+{{! Prettier stable }}
+<style lang="">
+  .a {
+    color: red;
+  }
+</style>
+
+{{! Prettier main }}
+<style lang="">
+  .a { color: red;
+  }
+</style>
+```
diff --git a/src/language-handlebars/embed.js b/src/language-handlebars/embed.js
index 62e86de08..035cf942c 100644
--- a/src/language-handlebars/embed.js
+++ b/src/language-handlebars/embed.js
@@ -23,8 +23,7 @@ function embed(path /* , options*/) {
     languageAttribute &&
     !(
       languageAttribute.value.type === "TextNode" &&
-      (languageAttribute.value.chars === "" ||
-        languageAttribute.value.chars === "css")
+      languageAttribute.value.chars === "css"
     )
   ) {
     return;
diff --git a/tests/format/handlebars/style-tag/__snapshots__/format.test.js.snap b/tests/format/handlebars/style-tag/__snapshots__/format.test.js.snap
index 6e2a9833e..117fc5dbc 100644
--- a/tests/format/handlebars/style-tag/__snapshots__/format.test.js.snap
+++ b/tests/format/handlebars/style-tag/__snapshots__/format.test.js.snap
@@ -134,26 +134,21 @@ parsers: ["glimmer"]
   </style>
 </div>
 
-=====================================output=====================================
-<div>
-  <style lang="css">
-    .a {
-      color: red;
-    }
-  </style>
-</div>
-================================================================================
-`;
-
-exports[`with-lang-attribute-2.hbs format 1`] = `
-====================================options=====================================
-parsers: ["glimmer"]
-                                                      printWidth: 80 (default) |
-=====================================input======================================
 <div>
   <style lang>
 
 
+    .a { color: red;
+    }
+
+
+  </style>
+</div>
+
+<div>
+  <style lang="">
+
+
     .a {color: red;
     }
 
@@ -161,22 +156,6 @@ parsers: ["glimmer"]
   </style>
 </div>
 
-=====================================output=====================================
-<div>
-  <style lang>
-    .a {
-      color: red;
-    }
-  </style>
-</div>
-================================================================================
-`;
-
-exports[`with-lang-attribute-3.hbs format 1`] = `
-====================================options=====================================
-parsers: ["glimmer"]
-                                                      printWidth: 80 (default) |
-=====================================input======================================
 
   <style lang="unknown">
 
@@ -188,6 +167,28 @@ parsers: ["glimmer"]
   </style>
 
 =====================================output=====================================
+<div>
+  <style lang="css">
+    .a {
+      color: red;
+    }
+  </style>
+</div>
+
+<div>
+  <style lang>
+    .a { color: red;
+    }
+  </style>
+</div>
+
+<div>
+  <style lang="">
+    .a {color: red;
+    }
+  </style>
+</div>
+
 <style lang="unknown">
   .a {color: red;
   }
diff --git a/tests/format/handlebars/style-tag/with-lang-attribute-2.hbs b/tests/format/handlebars/style-tag/with-lang-attribute-2.hbs
deleted file mode 100644
index 97de2990c..000000000
--- a/tests/format/handlebars/style-tag/with-lang-attribute-2.hbs
+++ /dev/null
@@ -1,10 +0,0 @@
-<div>
-  <style lang>
-
-
-    .a {color: red;
-    }
-
-
-  </style>
-</div>
diff --git a/tests/format/handlebars/style-tag/with-lang-attribute-3.hbs b/tests/format/handlebars/style-tag/with-lang-attribute-3.hbs
deleted file mode 100644
index 8f85a4c89..000000000
--- a/tests/format/handlebars/style-tag/with-lang-attribute-3.hbs
+++ /dev/null
@@ -1,9 +0,0 @@
-
-  <style lang="unknown">
-
-
-    .a {color: red;
-    }
-
-
-  </style>
diff --git a/tests/format/handlebars/style-tag/with-lang-attribute.hbs b/tests/format/handlebars/style-tag/with-lang-attribute.hbs
index efe82df55..daa895462 100644
--- a/tests/format/handlebars/style-tag/with-lang-attribute.hbs
+++ b/tests/format/handlebars/style-tag/with-lang-attribute.hbs
@@ -8,3 +8,35 @@
 
   </style>
 </div>
+
+<div>
+  <style lang>
+
+
+    .a { color: red;
+    }
+
+
+  </style>
+</div>
+
+<div>
+  <style lang="">
+
+
+    .a {color: red;
+    }
+
+
+  </style>
+</div>
+
+
+  <style lang="unknown">
+
+
+    .a {color: red;
+    }
+
+
+  </style>