Optional braces for model is (#673)

common/changes/@cadl-lang/compiler/optional-braces-for-is_2022-06-29-17-54.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@cadl-lang/compiler",
+      "comment": "Allow omitting braces from model is statements",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@cadl-lang/compiler"
+}

packages/compiler/core/parser.ts

@@ -674,7 +674,18 @@ export function parse(code: string | SourceFile, options: ParseOptions = {}): Ca
 
     const optionalExtends: TypeReferenceNode | undefined = parseOptionalModelExtends();
     const optionalIs = optionalExtends ? undefined : parseOptionalModelIs();
-    const properties = parseList(ListKind.ModelProperties, parseModelPropertyOrSpread);
+
+    let properties: (ModelPropertyNode | ModelSpreadPropertyNode)[] = [];
+    if (optionalIs) {
+      const tok = expectTokenIsOneOf(Token.Semicolon, Token.OpenBrace);
+      if (tok === Token.Semicolon) {
+        nextToken();
+      } else {
+        properties = parseList(ListKind.ModelProperties, parseModelPropertyOrSpread);
+      }
+    } else {
+      properties = parseList(ListKind.ModelProperties, parseModelPropertyOrSpread);
+    }
 
     return {
       kind: SyntaxKind.ModelStatement,

packages/compiler/test/parser.test.ts

@@ -93,6 +93,8 @@ describe("compiler: syntax", () => {
       "model Car { ... A.B, ... C<D> }",
 
       "model Car is Vehicle { }",
+
+      "model Car is Vehicle;",
     ]);
 
     parseErrorEach([
@@ -105,6 +107,9 @@ describe("compiler: syntax", () => {
         [/Cannot use default with non optional properties/],
       ],
       ["model", [/Identifier expected/]],
+      ["model Car is Vehicle", [/';', or '{' expected/]],
+      ["model Car;", [/'{', '=', 'extends', or 'is' expected/]],
+      ["model Car extends Foo;", [/'{' expected/]],
     ]);
   });
 

packages/spec/src/spec.emu.html

@@ -283,12 +283,19 @@ UsingStatement :
     `using` IdentifierOrMemberExpression `;`
 
 ModelStatement :
+    DecoratorList? `model` Identifier TemplateParameters? IsModelHeritage `;`
     DecoratorList? `model` Identifier TemplateParameters? ModelHeritage? `{` ModelBody? `}`
 
-ModelHeritage :
-    `extends` ReferenceExpression
+IsModelHeritage :
     `is` ReferenceExpression
 
+ExtendsModelHeritage :
+    `extends` ReferenceExpression
+
+ModelHeritage :
+    IsModelHeritage
+    ExtendsModelHeritage
+    
 ModelBody :
     ModelPropertyList `,`?
     ModelPropertyList `;`?