feat(openapi): richer info (description/termsOfService/contact/license) + top-level servers on App::openapi (FastAPI parity; servers 3.x-only, empty fields omitted).

Signed-off-by: 林晨 (Leo Cheng) <chengkelfan@qq.com>

Author: Lfan-ke

app_wbtest.mbt

@@ -255,3 +255,39 @@ test "openapi operation deprecated flag" {
   }
   assert_eq(has_dep, false)
 }
+
+///|
+test "openapi richer info: description/contact/license + servers" {
+  let app = App::new()
+  app.get("/ping", _ctx => text(200, "ok"))
+  let doc = app.openapi(
+    version=OpenApi31,
+    title="Greet",
+    description="qwq api",
+    contact=Some({ name: "heke1228", url: "", email: "emm@qq.com" }),
+    license=Some({ name: "Apache-2.0", url: "https://apache.org" }),
+    servers=[{ url: "https://api.example.com", description: "prod" }],
+  )
+  guard doc is Object(m) else { fail("doc should be an object") }
+  guard m.get("info") is Some(Object(info)) else {
+    fail("info should be present")
+  }
+  assert_eq(info.get("description"), Some("qwq api".to_json()))
+  guard info.get("contact") is Some(Object(c)) else {
+    fail("contact should be present")
+  }
+  assert_eq(c.get("name"), Some("heke1228".to_json()))
+  assert_eq(c.get("email"), Some("emm@qq.com".to_json()))
+  // An empty contact field is omitted, not emitted as "".
+  assert_eq(c.get("url"), None)
+  guard info.get("license") is Some(Object(l)) else {
+    fail("license should be present")
+  }
+  assert_eq(l.get("name"), Some("Apache-2.0".to_json()))
+  guard m.get("servers") is Some(Array(sv)) else {
+    fail("servers should be present")
+  }
+  assert_eq(sv.length(), 1)
+  guard sv[0] is Object(s0) else { fail("server should be an object") }
+  assert_eq(s0.get("url"), Some("https://api.example.com".to_json()))
+}

openapi.mbt

@@ -54,11 +54,41 @@ fn path_parameters(path : String, version : OpenApiVersion) -> Array[Json] {
 ///|
 /// Build the OpenAPI / Swagger document for the app as a `Json` value, walking
 /// the registered routes once into paths → methods → operations.
+/// OpenAPI `contact` info (← FastAPI's `contact`): every field optional, emitted
+/// only when non-empty.
+pub(all) struct Contact {
+  name : String
+  url : String
+  email : String
+}
+
+///|
+/// OpenAPI `license` info (← FastAPI's `license_info`): `name` required, `url`
+/// optional.
+pub(all) struct License {
+  name : String
+  url : String
+}
+
+///|
+/// A `servers` entry (← FastAPI's `servers`): a base URL and an optional
+/// description.
+pub(all) struct Server {
+  url : String
+  description : String
+}
+
+///|
 pub fn App::openapi(
   self : App,
   version? : OpenApiVersion = OpenApi31,
   title? : String = "moonapi",
   api_version? : String = "0.1.0",
+  description? : String = "",
+  terms_of_service? : String = "",
+  contact? : Contact? = None,
+  license? : License? = None,
+  servers? : Array[Server] = [],
 ) -> Json {
   let paths : Map[String, Json] = Map([])
   let defs : Map[String, Json] = Map([])
@@ -110,12 +140,64 @@ pub fn App::openapi(
     ("title", title.to_json()),
     ("version", api_version.to_json()),
   ])
+  if description != "" {
+    info["description"] = description.to_json()
+  }
+  if terms_of_service != "" {
+    info["termsOfService"] = terms_of_service.to_json()
+  }
+  match contact {
+    Some(c) => {
+      let cm : Map[String, Json] = Map([])
+      if c.name != "" {
+        cm["name"] = c.name.to_json()
+      }
+      if c.url != "" {
+        cm["url"] = c.url.to_json()
+      }
+      if c.email != "" {
+        cm["email"] = c.email.to_json()
+      }
+      if !cm.is_empty() {
+        info["contact"] = cm.to_json()
+      }
+    }
+    None => ()
+  }
+  match license {
+    Some(l) => {
+      let lm : Map[String, Json] = Map([("name", l.name.to_json())])
+      if l.url != "" {
+        lm["url"] = l.url.to_json()
+      }
+      info["license"] = lm.to_json()
+    }
+    None => ()
+  }
   let (root_key, version_str) = version_field(version)
   let doc : Map[String, Json] = Map([
     (root_key, version_str.to_json()),
     ("info", info.to_json()),
     ("paths", paths.to_json()),
   ])
+  // `servers` is an OpenAPI 3.x construct (2.0 uses host/basePath), so emit it
+  // only for the 3.x dialects.
+  if !servers.is_empty() {
+    match version {
+      Swagger20 => ()
+      _ => {
+        let sarr : Array[Json] = []
+        for s in servers {
+          let sm : Map[String, Json] = Map([("url", s.url.to_json())])
+          if s.description != "" {
+            sm["description"] = s.description.to_json()
+          }
+          sarr.push(sm.to_json())
+        }
+        doc["servers"] = sarr.to_json()
+      }
+    }
+  }
   // Hoisted named object schemas and the declared security schemes (the app's
   // own plus every mounted sub-app's): under `components` (`schemas` /
   // `securitySchemes`) in 3.x, or the top-level `definitions` /