Fix: Passing const of model type to @example (#4574)

fix #4544

.chronus/changes/fix-examples-const-2024-8-30-17-28-17.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/compiler"
+---
+
+Fix: Passing `const` of model type to `@example`

docs/standard-library/examples.md

@@ -65,6 +65,18 @@ model Pet {
 }
 ```
 
+### Define typed examples using `const`
+
+```tsp
+const petExample: Pet = #{ name: "Max", age: 3 };
+
+@example(petExample)
+model Pet {
+  name: string;
+  age: int32;
+}
+```
+
 ## Operation examples
 
 Operation example are provided with the `@opExample` decorator. Similar to the `@example` decorator the first argument is the example value however it takes both the `parameters` and `returnType` example.

packages/compiler/src/core/checker.ts

@@ -3921,7 +3921,6 @@ export function createChecker(program: Program): Checker {
         type.indexer = isBase.indexer;
       }
     }
-    decorators.push(...checkDecorators(type, node, mapper));
 
     if (isBase) {
       for (const prop of isBase.properties.values()) {
@@ -3957,6 +3956,8 @@ export function createChecker(program: Program): Checker {
     // Evaluate the properties after
     checkModelProperties(node, type.properties, type, mapper);
 
+    decorators.push(...checkDecorators(type, node, mapper));
+
     linkMapper(type, mapper);
 
     if (shouldCreateTypeForTemplate(node, mapper)) {

packages/compiler/test/decorators/examples.test.ts

@@ -47,6 +47,19 @@ describe("@example", () => {
       expect(serializeValueAsJson(program, examples[0].value, target)).toEqual({ a: 1, b: 2 });
     });
 
+    it("use const with type of model", async () => {
+      const { program, examples, target } = await getExamplesFor(`
+      const example: Test = #{ a: 1, b: 2 };
+      @example(example)
+      @test("test") model Test {
+        a: int32;
+        b: int32;
+      }
+    `);
+      expect(examples).toHaveLength(1);
+      expect(serializeValueAsJson(program, examples[0].value, target)).toEqual({ a: 1, b: 2 });
+    });
+
     it("emit diagnostic for missing property", async () => {
       const diagnostics = await diagnoseCode(`
         @example(#{ a: 1 })
@@ -98,6 +111,16 @@ describe("@example", () => {
       expect(serializeValueAsJson(program, examples[0].value, target)).toEqual("11:32");
     });
 
+    it("use const with type of scalar", async () => {
+      const { program, examples, target } = await getExamplesFor(`
+        const example: test = test.fromISO("11:32");
+        @example(example)
+        @test scalar test extends utcDateTime;
+      `);
+      expect(examples).toHaveLength(1);
+      expect(serializeValueAsJson(program, examples[0].value, target)).toEqual("11:32");
+    });
+
     it("emit diagnostic for unassignable value", async () => {
       const diagnostics = await diagnoseCode(`
         @example("11:32")
@@ -122,6 +145,19 @@ describe("@example", () => {
       expect(serializeValueAsJson(program, examples[0].value, target)).toEqual("a");
     });
 
+    it("use const with type of enum", async () => {
+      const { program, examples, target } = await getExamplesFor(`
+      const example: Test = Test.a;
+      @example(example)
+      @test("test") enum Test {
+        a,
+        b,
+      }
+    `);
+      expect(examples).toHaveLength(1);
+      expect(serializeValueAsJson(program, examples[0].value, target)).toEqual("a");
+    });
+
     it("emit diagnostic for unassignable value", async () => {
       const diagnostics = await diagnoseCode(`
         @example(1)