fix(compiler): only return undefined for no-arg scalar constructor, preserve args[0] behavior

Co-authored-by: markcowl <1054056+markcowl@users.noreply.github.com>

Author: Copilot

packages/compiler/src/lib/examples.ts

@@ -229,7 +229,11 @@ function serializeScalarValueAsJson(
 
   const result = resolveKnownScalar(program, value.scalar);
   if (result === undefined) {
-    return undefined;
+    const firstArg = value.value.args[0];
+    if (firstArg === undefined) {
+      return undefined;
+    }
+    return serializeValueAsJson(program, firstArg, firstArg.type);
   }
 
   encodeAs = encodeAs ?? result.encodeAs;

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

@@ -142,15 +142,15 @@ describe("@example", () => {
       expect(serializeValueAsJson(program, examples[0].value, target)).toBeUndefined();
     });
 
-    it("returns undefined for custom scalar with initializer", async () => {
+    it("serializes first argument for custom scalar with initializer", async () => {
       const { program, examples, target } = await getExamplesFor(`
-        @example(test.i("foo"))
+        @example(test.name("Shorty"))
         @test scalar test {
-          init i(s: string);
+          init name(value: string);
         }
       `);
       expect(examples).toHaveLength(1);
-      expect(serializeValueAsJson(program, examples[0].value, target)).toBeUndefined();
+      expect(serializeValueAsJson(program, examples[0].value, target)).toEqual("Shorty");
     });
   });
 

packages/openapi3/test/models.test.ts

@@ -275,6 +275,19 @@ worksFor(supportedVersions, ({ diagnoseOpenApiFor, oapiForModel, openApiFor }) =
     expect(res.schemas.Pet.properties.name.default).toEqual("Shorty");
   });
 
+  it("scalar with no-argument initializer used as a default value does not crash", async () => {
+    const res = await oapiForModel(
+      "M",
+      `
+        scalar S { init i(); }
+
+        model M { p: S = S.i(); }
+      `,
+    );
+
+    expect(res.schemas.M.properties.p.default).toBeUndefined();
+  });
+
   it("encode know scalar as a default value", async () => {
     const res = await oapiForModel(
       "Test",