Use Gulp to index demos (#6203)

build-scripts/gulp/gallery.js

@@ -1,7 +1,10 @@
 // Run demo develop mode
 const gulp = require("gulp");
+const fs = require("fs");
+const path = require("path");
 
 const env = require("../env");
+const paths = require("../paths");
 
 require("./clean.js");
 require("./translations.js");
@@ -12,6 +15,31 @@ require("./service-worker.js");
 require("./entry-html.js");
 require("./rollup.js");
 
+gulp.task("gather-gallery-demos", async function gatherDemos() {
+  const files = await fs.promises.readdir(
+    path.resolve(paths.gallery_dir, "src/demos")
+  );
+
+  let content = "export const DEMOS = {\n";
+
+  for (const file of files) {
+    const demoId = path.basename(file, ".ts");
+    const demoPath = "../src/demos/" + demoId;
+    content += `  "${demoId}": () => import("${demoPath}"),\n`;
+  }
+
+  content += "};";
+
+  const galleryBuild = path.resolve(paths.gallery_dir, "build");
+
+  fs.mkdirSync(galleryBuild, { recursive: true });
+  fs.writeFileSync(
+    path.resolve(galleryBuild, "import-demos.ts"),
+    content,
+    "utf-8"
+  );
+});
+
 gulp.task(
   "develop-gallery",
   gulp.series(
@@ -20,7 +48,11 @@ gulp.task(
     },
     "clean-gallery",
     "translations-enable-merge-backend",
-    gulp.parallel("gen-icons-json", "build-translations"),
+    gulp.parallel(
+      "gen-icons-json",
+      "build-translations",
+      "gather-gallery-demos"
+    ),
     "copy-static-gallery",
     "gen-index-gallery-dev",
     env.useRollup() ? "rollup-dev-server-gallery" : "webpack-dev-server-gallery"
@@ -35,7 +67,11 @@ gulp.task(
     },
     "clean-gallery",
     "translations-enable-merge-backend",
-    gulp.parallel("gen-icons-json", "build-translations"),
+    gulp.parallel(
+      "gen-icons-json",
+      "build-translations",
+      "gather-gallery-demos"
+    ),
     "copy-static-gallery",
     env.useRollup() ? "rollup-prod-gallery" : "webpack-prod-gallery",
     "gen-index-gallery-prod"