[handlebars] Named blocks can't be self closing (#11900)

changelog_unreleased/handlebars/11899.md

@@ -0,0 +1,23 @@
+#### Support Glimmer's named blocks (#11899 by @duailibe)
+
+Prettier already supported this feature, but it converted empty named blocks to self-closing, which is not supported by the Glimmer compiler.
+
+See: [Glimmer's named blocks](https://emberjs.github.io/rfcs/0460-yieldable-named-blocks.html).
+
+<!-- prettier-ignore -->
+```hbs
+// Input
+<Component>
+  <:named></:named>
+</Component>
+
+// Prettier stable
+<Component>
+  <:named />
+</Component>
+
+// Prettier main
+<Component>
+  <:named></:named>
+</Component>
+```

src/language-handlebars/utils.js

@@ -32,6 +32,7 @@ function isGlimmerComponent(node) {
   return (
     isNodeOfSomeType(node, ["ElementNode"]) &&
     typeof node.tag === "string" &&
+    node.tag[0] !== ":" &&
     (isUppercase(node.tag[0]) || node.tag.includes("."))
   );
 }

tests/format/handlebars/basics/__snapshots__/jsfmt.spec.js.snap

@@ -93,6 +93,30 @@ printWidth: 80
 ================================================================================
 `;
 
+exports[`named-block.hbs format 1`] = `
+====================================options=====================================
+parsers: ["glimmer"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+<ComponentWithNamedBlocks>
+  <:first-named-block></:first-named-block>
+  <:second-named-block> </:second-named-block>
+  <:named-block-with-comment>{{! Do not convert to an empty element}}</:named-block-with-comment>
+  <:named-block-with-content>Hello</:named-block-with-content>
+</ComponentWithNamedBlocks>
+
+=====================================output=====================================
+<ComponentWithNamedBlocks>
+  <:first-named-block></:first-named-block>
+  <:second-named-block> </:second-named-block>
+  <:named-block-with-comment
+  >{{! Do not convert to an empty element}}</:named-block-with-comment>
+  <:named-block-with-content>Hello</:named-block-with-content>
+</ComponentWithNamedBlocks>
+================================================================================
+`;
+
 exports[`nested-path.hbs format 1`] = `
 ====================================options=====================================
 parsers: ["glimmer"]

tests/format/handlebars/basics/named-block.hbs

@@ -0,0 +1,6 @@
+<ComponentWithNamedBlocks>
+  <:first-named-block></:first-named-block>
+  <:second-named-block> </:second-named-block>
+  <:named-block-with-comment>{{! Do not convert to an empty element}}</:named-block-with-comment>
+  <:named-block-with-content>Hello</:named-block-with-content>
+</ComponentWithNamedBlocks>