Default values supporting scalar and object

.chronus/changes/almend-ScalarDefaultValue-2024-8-12-15-34-32.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/openapi3"
+---
+
+Added support to use Scalar and Object as default types

packages/openapi3/src/lib.ts

@@ -239,12 +239,6 @@ export const libDef = {
         default: "Enums are not supported unless all options are literals of the same type.",
       },
     },
-    "invalid-default": {
-      severity: "error",
-      messages: {
-        default: paramMessage`Invalid type '${"type"}' for a default value`,
-      },
-    },
     "inline-cycle": {
       severity: "error",
       messages: {

packages/openapi3/src/openapi.ts

@@ -395,7 +395,7 @@ function createOAPIEmitter(
         }
 
         const variable: OpenAPI3ServerVariable = {
-          default: prop.defaultValue ? getDefaultValue(program, prop.defaultValue) : "",
+          default: prop.defaultValue ? getDefaultValue(program, prop.defaultValue, prop) : "",
           description: getDoc(program, prop),
         };
 
@@ -1371,7 +1371,7 @@ function createOAPIEmitter(
       options,
     );
     if (param.defaultValue) {
-      schema.default = getDefaultValue(program, param.defaultValue);
+      schema.default = getDefaultValue(program, param.defaultValue, param);
     }
     // Description is already provided in the parameter itself.
     delete schema.description;

packages/openapi3/src/schema-emitter.ts

@@ -377,7 +377,7 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     // Apply decorators on the property to the type's schema
     const additionalProps: Partial<OpenAPI3Schema> = this.#applyConstraints(prop, {});
     if (prop.defaultValue) {
-      additionalProps.default = getDefaultValue(program, prop.defaultValue);
+      additionalProps.default = getDefaultValue(program, prop.defaultValue, prop);
     }
 
     if (isReadonlyProperty(program, prop)) {
@@ -922,27 +922,12 @@ const B = {
   },
 } as const;
 
-export function getDefaultValue(program: Program, defaultType: Value): any {
-  switch (defaultType.valueKind) {
-    case "StringValue":
-      return defaultType.value;
-    case "NumericValue":
-      return defaultType.value.asNumber() ?? undefined;
-    case "BooleanValue":
-      return defaultType.value;
-    case "ArrayValue":
-      return defaultType.values.map((x) => getDefaultValue(program, x));
-    case "NullValue":
-      return null;
-    case "EnumValue":
-      return defaultType.value.value ?? defaultType.value.name;
-    default:
-      reportDiagnostic(program, {
-        code: "invalid-default",
-        format: { type: defaultType.valueKind },
-        target: defaultType,
-      });
-  }
+export function getDefaultValue(
+  program: Program,
+  defaultType: Value,
+  modelProperty: ModelProperty,
+): any {
+  return serializeValueAsJson(program, defaultType, modelProperty);
 }
 
 export function isBytesKeptRaw(program: Program, type: Type) {

packages/openapi3/test/models.test.ts

@@ -259,6 +259,41 @@ describe("openapi3: models", () => {
     });
   });
 
+  it("scalar used as a default value", async () => {
+    const res = await oapiForModel(
+      "Pet",
+      `
+        scalar shortName { init name(value: string);}
+
+        model Pet { name: shortName = shortName.name("Shorty"); }
+      `,
+    );
+
+    expect(res.schemas.Pet.properties.name.default).toEqual("Shorty");
+  });
+
+  it("encode know scalar as a default value", async () => {
+    const res = await oapiForModel(
+      "Test",
+      `
+        model Test { @encode("rfc7231") minDate: utcDateTime = utcDateTime.fromISO("2024-01-01T11:32:00Z"); }
+      `,
+    );
+
+    expect(res.schemas.Test.properties.minDate.default).toEqual("Mon, 01 Jan 2024 11:32:00 GMT");
+  });
+
+  it("object value used as a default value", async () => {
+    const res = await oapiForModel(
+      "Test",
+      `
+        model Test { Pet: {name: string;} = #{ name: "Dog"}; }
+      `,
+    );
+
+    expect(res.schemas.Test.properties.Pet.default.name).toEqual("Dog");
+  });
+
   describe("numeric defaults", () => {
     it.each([
       ["0.01", 0.01],