Some comments

bookshop/server.js

@@ -1,11 +1,16 @@
+// Serves a Swagger UI with API definitions either created on the fly
+// or loaded from file system.
+//
+// Needs @sap/cds-dk >= 3.3.0 installed
+
 const {resolve} = require ('path')
 const {promisify} = require('util')
 const readFile = promisify(require('fs').readFile)
 const swaggerUi = require ('swagger-ui-express')
 const cds = require ('@sap/cds')
-const trace = cds.debug('openapi')
 const cors = require('cors')
 
+const debug = cds.debug('openapi')
 let app, docCache={}
 
 cds
@@ -29,8 +34,9 @@ async function toOpenApiDoc(service, cache) {
     if (spec) {  // pre-compiled spec file available?
       cache[service.name] = spec
     }
-    else if (cds.compile.to.openapi) {  // on-the-fly exporter available?
-      trace && trace ('Compiling Open API spec for', service.name)
+    // On-the-fly exporter available?  Needs @sap/cds-dk >= 3.3.0
+    else if (cds.compile.to.openapi) {
+      debug && debug ('Compiling Open API spec for', service.name)
       cache[service.name] = cds.compile.to.openapi (service.model, {
         service: service.name,
         'openapi:url': service.path,
@@ -45,7 +51,7 @@ async function openApiFromFile(service) {
   const fileName = resolve(`srv/${service.name}.openapi3.json`)
   const file = await readFile(fileName).catch(()=>{/*no such file*/})
   if (file) {
-    trace && trace ('Using Open API spec from file', fileName)
+    debug && debug ('Using Open API spec from file', fileName)
     return JSON.parse(file)
   }
 }
@@ -55,6 +61,7 @@ function addLinkToIndexHtml(service, apiPath) {
     if (entity)  return // avoid link on entity level, looks too messy
     return { href:apiPath, name:'Swagger UI', title:'Show in Swagger UI' }
   }
+  // Needs @sap/cds >= 4.4.0
   service.$linkProviders ? service.$linkProviders.push(provider) : service.$linkProviders = [provider]
 }