Build all ad extensions with amp-ad (#17291)

* build all ad extensions

* approach 2

* add comment

gulpfile.js

@@ -57,6 +57,9 @@ const hostname3p = argv.hostname3p || '3p.ampproject.net';
 const extensions = {};
 const extensionAliasFilePath = {};
 
+// All a4a extensions.
+const adVendors = [];
+
 const {green, red, cyan} = colors;
 
 const minifiedRuntimeTarget = 'dist/v0.js';
@@ -139,6 +142,12 @@ function declareExtension(name, version, options) {
     extensions[`${name}-${v}`] =
         Object.assign({name, version: v}, defaultOptions, options);
   });
+  if (name.startsWith('amp-ad-network-')) {
+    // Get the ad network name. All ad network extensions are named
+    // in the format `amp-ad-network-${name}-impl`
+    name = name.slice(15, -5);
+    adVendors.push(name);
+  }
 }
 
 /**
@@ -260,10 +269,22 @@ function getExtensionsFromArg(examples) {
     const html = fs.readFileSync(example, 'utf8');
     const customElementTemplateRe = /custom-(element|template)="([^"]+)"/g;
     const extensionNameMatchIndex = 2;
+    let hasAd = false;
     let match;
     while ((match = customElementTemplateRe.exec(html))) {
+      if (match[extensionNameMatchIndex] == 'amp-ad') {
+        hasAd = true;
+      }
       extensions.push(match[extensionNameMatchIndex]);
     }
+    if (hasAd) {
+      for (let i = 0; i < adVendors.length; i++) {
+        if (html.includes(`type="${adVendors[i]}"`)) {
+          extensions.push('amp-a4a');
+          extensions.push(`amp-ad-network-${adVendors[i]}-impl`);
+        }
+      }
+    }
   });
 
   return dedupe(extensions);