Correctly handle <:inverse> named block

packages/@glimmer/compiler/lib/passes/2-encoding/content.ts

@@ -180,7 +180,11 @@ export class ContentEncoder {
   }
 
   NamedBlock({ name, body, scope }: mir.NamedBlock): WireFormat.Core.NamedBlock {
-    return [name.chars, [CONTENT.list(body), scope.slots]];
+    let nameChars = name.chars;
+    if (nameChars === 'inverse') {
+      nameChars = 'else';
+    }
+    return [nameChars, [CONTENT.list(body), scope.slots]];
   }
 
   If({ condition, block, inverse }: mir.If): WireFormat.Statements.If {

packages/@glimmer/integration-tests/lib/suites/emberish-components.ts

@@ -268,6 +268,23 @@ export class EmberishComponentTests extends RenderTest {
     this.assertStableRerender();
   }
 
+  @test({ kind: 'curly' })
+  'inverse named block'() {
+    class FooBar extends EmberishCurlyComponent {
+      [index: string]: unknown;
+
+      constructor() {
+        super();
+      }
+    }
+    this.registerComponent('Curly', 'FooBar', 'Hello{{yield "my" to="inverse"}}world!', FooBar);
+
+    this.render(`<FooBar><:inverse as |value|> {{value}} </:inverse></FooBar>`);
+
+    this.assertComponent('Hello my world!');
+    this.assertStableRerender();
+  }
+
   @test({ kind: 'curly' })
   'invoking wrapped layout via angle brackets - invocation attributes merges classes'() {
     class FooBar extends EmberishCurlyComponent {

packages/@glimmer/integration-tests/test/syntax/named-blocks-test.ts

@@ -35,6 +35,24 @@ class NamedBlocksSyntaxErrors extends RenderTest {
     }, syntaxErrorFor('Component had two named blocks with the same name, `<:foo>`. Only one block with a given name may be passed', '<Foo><:foo></:foo><:foo></:foo></Foo>', 'test-module', 1, 0));
   }
 
+  @test
+  'Throws an error if both inverse and else named blocks are passed, inverse first'() {
+    this.assert.throws(() => {
+      preprocess('<Foo><:inverse></:inverse><:else></:else></Foo>', {
+        meta: { moduleName: 'test-module' },
+      });
+    }, syntaxErrorFor('Component has both <:else> and <:inverse> block. <:inverse> is an alias for <:else>', '<Foo><:inverse></:inverse><:else></:else></Foo>', 'test-module', 1, 0));
+  }
+
+  @test
+  'Throws an error if both inverse and else named blocks are passed, else first'() {
+    this.assert.throws(() => {
+      preprocess('<Foo><:else></:else><:inverse></:inverse></Foo>', {
+        meta: { moduleName: 'test-module' },
+      });
+    }, syntaxErrorFor('Component has both <:else> and <:inverse> block. <:inverse> is an alias for <:else>', '<Foo><:else></:else><:inverse></:inverse></Foo>', 'test-module', 1, 0));
+  }
+
   @test
   'Throws an error if there is content outside of the blocks'() {
     this.assert.throws(() => {

packages/@glimmer/syntax/lib/v2-a/normalize.ts

@@ -906,6 +906,16 @@ class ElementChildren extends Children {
           );
         }
 
+        if (
+          (name === 'inverse' && seenNames.has('else')) ||
+          (name === 'else' && seenNames.has('inverse'))
+        ) {
+          throw generateSyntaxError(
+            `Component has both <:else> and <:inverse> block. <:inverse> is an alias for <:else>`,
+            this.loc
+          );
+        }
+
         seenNames.add(name);
       }