Keep is/extends inline for multi-argument template heritage

.chronus/changes/fix-formatter-heritage-keyword-break-2026-6-18.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/compiler"
+---
+
+Keep the `is`/`extends` keyword on the declaration line when the base is a template reference with multiple arguments. The template argument list now controls the line breaking instead of the keyword being pushed onto its own indented line.

.chronus/changes/fix-formatter-heritage-keyword-break-java-2026-6-18.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/http-client-java"
+---
+
+Reformat a test spec affected by the compiler formatter change keeping `is`/`extends` inline for multi-argument template references (whitespace only, no semantic change).

packages/compiler/src/formatter/print/printer.ts

@@ -1043,17 +1043,40 @@ export function printArrayLiteral(
   ]);
 }
 
+// When the base is a multi-argument template, its argument list breaks on its
+// own, so keep `is`/`extends` inline instead of breaking the keyword too (#11009).
+function printHeritageClause<T extends Node>(
+  path: AstPath<T>,
+  print: PrettierChildPrint,
+  keyword: string,
+  propertyName: keyof T,
+): Doc {
+  const ref = path.node[propertyName] as Node | undefined;
+  if (!ref) {
+    return "";
+  }
+  const printed = [`${keyword} `, path.call(print, propertyName as any)];
+  if (isMultiArgTemplateReference(ref)) {
+    return [" ", printed];
+  }
+  return group(indent([ifBreak(line, " "), printed]));
+}
+
+function isMultiArgTemplateReference(node: Node): boolean {
+  return (
+    node.kind === SyntaxKind.TypeReference && (node as TypeReferenceNode).arguments.length >= 2
+  );
+}
+
 export function printModelStatement(
   path: AstPath<ModelStatementNode>,
   options: TypeSpecPrettierOptions,
   print: PrettierChildPrint,
 ) {
   const node = path.node;
   const id = path.call(print, "id");
-  const heritage = node.extends
-    ? [ifBreak(line, " "), "extends ", path.call(print, "extends")]
-    : "";
-  const isBase = node.is ? [ifBreak(line, " "), "is ", path.call(print, "is")] : "";
+  const heritage = printHeritageClause(path, print, "extends", "extends");
+  const isBase = printHeritageClause(path, print, "is", "is");
   const generic = printTemplateParameters(path, options, print, "templateParameters");
   const nodeHasComments = hasComments(node, CommentCheckFlags.Dangling);
   const shouldPrintBody = nodeHasComments || !(node.properties.length === 0 && node.is);
@@ -1064,7 +1087,8 @@ export function printModelStatement(
     "model ",
     id,
     generic,
-    group(indent(["", heritage, isBase])),
+    heritage,
+    isBase,
     body,
   ];
 }
@@ -1240,9 +1264,7 @@ function printScalarStatement(
   const id = path.call(print, "id");
   const template = printTemplateParameters(path, options, print, "templateParameters");
 
-  const heritage = node.extends
-    ? [ifBreak(line, " "), "extends ", path.call(print, "extends")]
-    : "";
+  const heritage = printHeritageClause(path, print, "extends", "extends");
   const nodeHasComments = hasComments(node, CommentCheckFlags.Dangling);
   const shouldPrintBody = nodeHasComments || !(node.members.length === 0);
 
@@ -1253,7 +1275,7 @@ function printScalarStatement(
     "scalar ",
     id,
     template,
-    group(indent(["", heritage])),
+    heritage,
     members,
   ];
 }

packages/compiler/test/formatter/formatter.test.ts

@@ -207,6 +207,21 @@ model   Foo extends SuperExtremeAndVeryVeryVeryVeryVeryVeryLongModelThatWillBeTo
           expected: `
 model Foo
   extends SuperExtremeAndVeryVeryVeryVeryVeryVeryLongModelThatWillBeTooLong {}
+`,
+        });
+      });
+
+      it("keeps extends inline and breaks the template arguments when too long", async () => {
+        await assertFormat({
+          code: `
+model Foo extends Base<FirstArgumentTypeName, SecondArgumentTypeName, ThirdArgumentTypeName> {}
+`,
+          expected: `
+model Foo extends Base<
+  FirstArgumentTypeName,
+  SecondArgumentTypeName,
+  ThirdArgumentTypeName
+> {}
 `,
         });
       });
@@ -255,6 +270,21 @@ model   Foo is SuperExtremeAndVeryVeryVeryVeryVeryVeryLongLongLongModelThatWillB
           expected: `
 model Foo
   is SuperExtremeAndVeryVeryVeryVeryVeryVeryLongLongLongModelThatWillBeTooLong;
+`,
+        });
+      });
+
+      it("keeps is inline and breaks the template arguments when too long", async () => {
+        await assertFormat({
+          code: `
+model Foo is Base<FirstArgumentTypeName, SecondArgumentTypeName, ThirdArgumentTypeName>;
+`,
+          expected: `
+model Foo is Base<
+  FirstArgumentTypeName,
+  SecondArgumentTypeName,
+  ThirdArgumentTypeName
+>;
 `,
         });
       });
@@ -809,6 +839,21 @@ scalar Foo extends string;
       });
     });
 
+    it("keeps extends inline and breaks the template arguments when too long", async () => {
+      await assertFormat({
+        code: `
+scalar Foo extends Base<FirstArgumentTypeName, SecondArgumentTypeName, ThirdArgumentTypeName>;
+`,
+        expected: `
+scalar Foo extends Base<
+  FirstArgumentTypeName,
+  SecondArgumentTypeName,
+  ThirdArgumentTypeName
+>;
+`,
+      });
+    });
+
     it("format with template parameters", async () => {
       await assertFormat({
         code: `

packages/http-client-java/generator/http-client-generator-test/tsp/arm-customization.tsp

@@ -23,8 +23,10 @@ enum Versions {
   v2023_12_01_preview: "2023-12-01-preview",
 }
 
-model Vault
-  is Azure.ResourceManager.Legacy.TrackedResourceWithOptionalLocation<VaultProperties, false> {
+model Vault is Azure.ResourceManager.Legacy.TrackedResourceWithOptionalLocation<
+  VaultProperties,
+  false
+> {
   ...ResourceNameParameter<
     Resource = Vault,
     KeyName = "vaultName",

website/src/content/docs/release-notes/typespec-1-11-0.mdx

@@ -31,12 +31,11 @@ model Example {
   description: string;
 }
 
-model CreateAndReadExample
-  is FilterVisibility<
-    Example,
-    #{ all: #[Lifecycle.Create, Lifecycle.Read] },
-    "CreateAndRead{name}"
-  >;
+model CreateAndReadExample is FilterVisibility<
+  Example,
+  #{ all: #[Lifecycle.Create, Lifecycle.Read] },
+  "CreateAndRead{name}"
+>;
 ```
 
 :::caution