[wip] sketching watch API

This is just a toy example to motivate a watch api for virtual content.

Along the way we discovered that vite incorectly implements rollups `addWatchFile` API because (1) it's supposed to accept directories and doesn't and (2) it's supposed to resolve relative paths relative to the current working directory, not the current request.

packages/core/src/module-resolver.ts

@@ -160,6 +160,10 @@ export class Resolver {
   constructor(readonly options: Options) {}
 
   beforeResolve<R extends ModuleRequest>(request: R): R {
+    if (request.specifier === '#the-file-list') {
+      return request.virtualize('/the-file-list');
+    }
+
     if (request.specifier === '@embroider/macros') {
       // the macros package is always handled directly within babel (not
       // necessarily as a real resolvable package), so we should not mess with it.

packages/core/src/node-resolve.ts

@@ -56,7 +56,7 @@ export function nodeResolve(
           type: 'found',
           result: {
             type: 'virtual' as 'virtual',
-            content: virtualContent(request.specifier, resolver),
+            content: virtualContent(request.specifier, resolver).src,
             filename: request.specifier,
           },
         };

packages/core/src/virtual-content.ts

@@ -2,6 +2,7 @@ import { dirname, basename, resolve, posix, sep, join } from 'path';
 import type { Resolver, AddonPackage, Package } from '.';
 import { explicitRelative, extensionsPattern } from '.';
 import { compile } from './js-handlebars';
+import { readdirSync } from 'fs-extra';
 
 const externalESPrefix = '/@embroider/ext-es/';
 const externalCJSPrefix = '/@embroider/ext-cjs/';
@@ -10,29 +11,40 @@ const externalCJSPrefix = '/@embroider/ext-cjs/';
 // this produces the corresponding contents. It's a static, stateless function
 // because we recognize that that process that did resolution might not be the
 // same one that loads the content.
-export function virtualContent(filename: string, resolver: Resolver): string {
+export function virtualContent(filename: string, resolver: Resolver): { src: string; watches: string[] } {
+  if (filename === '/the-file-list') {
+    let dir = join(resolver.options.appRoot, 'app');
+    let files = readdirSync(dir);
+    return {
+      src: `export default [
+      ${files.map(f => `"${f}"`).join(',')}
+    ]`,
+      watches: [join(resolver.options.appRoot, 'app', 'app.js')],
+    };
+  }
+
   let cjsExtern = decodeVirtualExternalCJSModule(filename);
   if (cjsExtern) {
-    return renderCJSExternalShim(cjsExtern);
+    return { src: renderCJSExternalShim(cjsExtern), watches: [] };
   }
 
   let extern = decodeVirtualExternalESModule(filename);
   if (extern) {
-    return renderESExternalShim(extern);
+    return { src: renderESExternalShim(extern), watches: [] };
   }
   let match = decodeVirtualPairComponent(filename);
   if (match) {
-    return pairedComponentShim(match);
+    return { src: pairedComponentShim(match), watches: [] };
   }
 
   let fb = decodeFastbootSwitch(filename);
   if (fb) {
-    return fastbootSwitchTemplate(fb);
+    return { src: fastbootSwitchTemplate(fb), watches: [] };
   }
 
   let im = decodeImplicitModules(filename);
   if (im) {
-    return renderImplicitModules(im, resolver);
+    return { src: renderImplicitModules(im, resolver), watches: [] };
   }
 
   throw new Error(`not an @embroider/core virtual file: ${filename}`);

packages/vite/src/esbuild-resolver.ts

@@ -39,7 +39,7 @@ export function esBuildResolver(root = process.cwd()): EsBuildPlugin {
       });
 
       build.onLoad({ namespace: 'embroider', filter: /./ }, ({ path }) => {
-        let src = virtualContent(path, resolverLoader.resolver);
+        let { src } = virtualContent(path, resolverLoader.resolver);
         if (!macrosConfig) {
           macrosConfig = readJSONSync(
             resolve(locateEmbroiderWorkingDir(root), 'rewritten-app', 'macros-config.json')
@@ -82,7 +82,7 @@ export function esBuildResolver(root = process.cwd()): EsBuildPlugin {
       build.onLoad({ filter: /\.[jt]s$/ }, ({ path, namespace }) => {
         let src: string;
         if (namespace === 'embroider') {
-          src = virtualContent(path, resolverLoader.resolver);
+          src = virtualContent(path, resolverLoader.resolver).src;
         } else {
           src = readFileSync(path, 'utf8');
         }

packages/vite/src/resolver.ts

@@ -29,7 +29,11 @@ export function resolver(): Plugin {
     },
     load(id) {
       if (id.startsWith(virtualPrefix)) {
-        return virtualContent(id.slice(virtualPrefix.length), resolverLoader.resolver);
+        let { src, watches } = virtualContent(id.slice(virtualPrefix.length), resolverLoader.resolver);
+        for (let watch of watches) {
+          this.addWatchFile(watch);
+        }
+        return src;
       }
     },
   };