ui: Replace plugin barrel codegen with a Vite virtual module (#5903)

The `plugin`/`core_plugin` import barrels are currently generated by a
Python script (`tools/gen_ui_imports`) that write .ts and .scss files
into ui/src/gen.

This patch moves the .ts barrels into a Vite plugin that exposes them as
virtual modules:

```ts
import NON_CORE_PLUGINS from 'virtual:perfetto/all_plugins';
import CORE_PLUGINS from 'virtual:perfetto/all_core_plugins';
```

The .scss barrel is gone too — each plugin's index.ts now does `import
'./styles.scss'` so Vite pulls plugin styles in via the JS module graph
instead of a separate aggregated SCSS file.

Drops the tools/gen_ui_imports script and its build.mjs invocations.

By virtue of the added d.ts file, this makes the plugin list types
available before the barrel file has been generated, getting us closer
to a world where the typescript build can be checked before any
artifacts are generated.

Author: stevegolton

python/tools/check_imports.py

@@ -34,7 +34,10 @@
 # [a,b] -> [c,d] is equivalent to allowing a>c, a>d, b>c, b>d.
 DEPS_ALLOWLIST = [
     # Everything can depend on base/, protos and NPM packages.
-    ('*', ['/base/*', '/protos/index', '/gen/perfetto_version', NODE_MODULES]),
+    ('*', [
+        '/base/*', '/protos/index', '/gen/perfetto_version', NODE_MODULES,
+        'virtual:*'
+    ]),
 
     # Integration tests can depend on everything.
     ('/test/*', '*'),

tools/gen_ui_imports

@@ -77,7 +77,6 @@ const __dirname = path.dirname(__filename);
 
 const ROOT_DIR = path.dirname(__dirname); // The repo root.
 const VERSION_SCRIPT = pjoin(ROOT_DIR, 'tools/write_version_header.py');
-const GEN_IMPORTS_SCRIPT = pjoin(ROOT_DIR, 'tools/gen_ui_imports');
 const DEFAULT_PORT = 10000;
 
 const cfg = {
@@ -379,8 +378,6 @@ Env-var overrides:
 
     buildWasm(args.no_wasm);
     copySyntaqliteRuntime();
-    generateImports('ui/src/core_plugins', 'all_core_plugins');
-    generateImports('ui/src/plugins', 'all_plugins');
     scanDir('ui/src/assets');
     scanDir('ui/src/chrome_extension');
     scanDir('buildtools/typefaces');
@@ -566,19 +563,6 @@ function compileProtos() {
   addTask(execModule, ['pbts', pbtsArgs]);
 }
 
-function generateImports(dir, name) {
-  // We have to use the symlink (ui/src/gen) rather than cfg.outGenDir
-  // below since we want to generate the correct relative imports. For example:
-  // ui/src/frontend/foo.ts
-  //    import '../gen/all_plugins.ts';
-  // ui/src/gen/all_plugins.ts (aka ui/out/tsc/gen/all_plugins.ts)
-  //    import '../frontend/some_plugin.ts';
-  const dstTs = pjoin(ROOT_DIR, 'ui/src/gen', name);
-  const inputDir = pjoin(ROOT_DIR, dir);
-  const args = [GEN_IMPORTS_SCRIPT, inputDir, '--out', dstTs];
-  addTask(exec, ['python3', args]);
-}
-
 // Generates a .ts source that defines the VERSION and SCM_REVISION constants.
 function genVersion() {
   const cmd = 'python3';

ui/build.mjs

@@ -17,8 +17,8 @@ import '../base/disposable_polyfill';
 import '../base/static_initializers';
 import '../assets/perfetto.scss';
 import z from 'zod';
-import NON_CORE_PLUGINS from '../gen/all_plugins';
-import CORE_PLUGINS from '../gen/all_core_plugins';
+import NON_CORE_PLUGINS from 'virtual:perfetto/all_plugins';
+import CORE_PLUGINS from 'virtual:perfetto/all_core_plugins';
 import m from 'mithril';
 import {defer} from '../base/deferred';
 import {addErrorHandler, reportError} from '../base/logging';

ui/src/frontend/index.ts

@@ -0,0 +1,36 @@
+// Copyright (C) 2026 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Type declarations for virtual modules generated by Vite plugins. See
+// pluginAllPluginsBarrel in ui/vite.config.mjs.
+//
+// NB: this file must be an ambient script (no top-level imports), otherwise
+// the `declare module` blocks would become module-scoped and tsc wouldn't
+// pick them up when resolving the `virtual:` imports elsewhere. Imports
+// inside a `declare module` block can't be relative, so we go via baseUrl.
+
+declare module 'virtual:perfetto/all_plugins' {
+  // Putting the imports here rather than hoisting to the top of the file keeps
+  // this as an ambient script, which is required in order to get tsc to pick up
+  // the module declarations.
+  import type {PerfettoPluginStatic, PerfettoPlugin} from 'src/public/plugin';
+  const plugins: PerfettoPluginStatic<PerfettoPlugin>[];
+  export default plugins;
+}
+
+declare module 'virtual:perfetto/all_core_plugins' {
+  import type {PerfettoPluginStatic, PerfettoPlugin} from 'src/public/plugin';
+  const plugins: PerfettoPluginStatic<PerfettoPlugin>[];
+  export default plugins;
+}

ui/src/types/virtual-modules.d.ts

@@ -103,6 +103,82 @@ function pluginEmbedMinimalSourceMap() {
   };
 }
 
+// Generates barrel modules that import every plugin under ui/src/plugins (or
+// ui/src/core_plugins) and default-export an array of their default exports.
+// Replaces the on-disk barrels that tools/gen_ui_imports used to produce.
+//
+// Exposed as virtual modules so consumers do:
+//   import NON_CORE_PLUGINS from 'virtual:perfetto/all_plugins';
+//   import CORE_PLUGINS     from 'virtual:perfetto/all_core_plugins';
+//
+// Types live in ui/src/types/virtual-modules.d.ts.
+function pluginAllPluginsBarrel() {
+  const VIRTUALS = {
+    'virtual:perfetto/all_plugins':      path.join(SRC, 'plugins'),
+    'virtual:perfetto/all_core_plugins': path.join(SRC, 'core_plugins'),
+  };
+  const toCamelCase = (s) => {
+    const [first, ...rest] = s.split(/[._]/);
+    return first +
+        rest.map((x) => x.charAt(0).toUpperCase() + x.slice(1)).join('');
+  };
+  const generate = (dir) => {
+    const entries = fs.readdirSync(dir)
+      .map((name) => ({name, full: path.join(dir, name)}))
+      .filter(({full}) => {
+        try {
+          return fs.statSync(full).isDirectory() &&
+                 fs.existsSync(path.join(full, 'index.ts'));
+        } catch (_) { return false; }
+      })
+      .sort((a, b) => a.name.localeCompare(b.name));
+    const imports = entries
+      .map(({name, full}) => `import ${toCamelCase(name)} from '${full}';`)
+      .join('\n');
+    const arr = entries.map(({name}) => `  ${toCamelCase(name)},`).join('\n');
+    return `${imports}\n\nexport default [\n${arr}\n];\n`;
+  };
+  let server = null;
+  return {
+    name: 'perfetto:all-plugins-barrel',
+    configureServer(s) {
+      server = s;
+      // Watch the parent dirs so adding/removing a plugin dir invalidates
+      // the barrel even before any file inside it changes. addWatchFile in
+      // load() only covers index.ts files that already exist at load time.
+      for (const dir of Object.values(VIRTUALS)) s.watcher.add(dir);
+    },
+    resolveId(id) {
+      if (id in VIRTUALS) return '\0' + id;
+    },
+    load(id) {
+      if (!id.startsWith('\0virtual:perfetto/')) return;
+      const realId = id.slice(1);
+      const dir = VIRTUALS[realId];
+      if (!dir) return;
+      // Tell Rollup we depend on every index.ts so edits/deletes trigger
+      // a rebuild in `vite build --watch`.
+      for (const name of fs.readdirSync(dir)) {
+        const idx = path.join(dir, name, 'index.ts');
+        if (fs.existsSync(idx)) this.addWatchFile(idx);
+      }
+      return generate(dir);
+    },
+    handleHotUpdate(ctx) {
+      // Invalidate the matching barrel when any file under one of the
+      // plugin parent dirs is added/changed/removed (catches new plugin
+      // dirs being dropped in). Edits to existing plugin source don't need
+      // to invalidate the barrel itself — Vite handles those normally.
+      if (!server) return;
+      for (const [realId, dir] of Object.entries(VIRTUALS)) {
+        if (!ctx.file.startsWith(dir + path.sep)) continue;
+        const mod = server.moduleGraph.getModuleById('\0' + realId);
+        if (mod) server.moduleGraph.invalidateModule(mod);
+      }
+    },
+  };
+}
+
 function pluginGenRelativeImports() {
   return {
     name: 'perfetto:gen-relative-imports',
@@ -151,6 +227,7 @@ export default defineConfig({
   // No HTML index — build.mjs handles HTML.
   appType: 'custom',
   plugins: [
+    pluginAllPluginsBarrel(),
     pluginGenRelativeImports(),
     ...(NO_SOURCE_MAPS ? [] : [pluginEmbedMinimalSourceMap()]),
   ],