feat: support rollup plugin this.load in plugin container context

packages/vite/src/node/server/__tests__/pluginContainer.spec.ts

@@ -147,6 +147,44 @@ describe('plugin container', () => {
       expect.assertions(2)
     })
   })
+
+  describe('load', () => {
+    beforeEach(() => {
+      moduleGraph = new ModuleGraph((id) => resolveId(id))
+    })
+
+    it('can resolve a secondary module', async () => {
+      const entryUrl = '/x.js'
+
+      const plugin: Plugin = {
+        name: 'p1',
+        resolveId(id) {
+          return id
+        },
+        load(id) {
+          if (id === entryUrl) return { code: '1', meta: { x: 1 } }
+          else return { code: '2', meta: { x: 2 } }
+        },
+        async transform(code, id) {
+          if (id === entryUrl)
+            return {
+              code: `${
+                (await this.load({ id: '/secondary.js' })).meta.x || undefined
+              }`,
+            }
+          return { code }
+        },
+      }
+
+      const container = await getPluginContainer({
+        plugins: [plugin],
+      })
+      await moduleGraph.ensureEntryFromUrl(entryUrl, false)
+      const loadResult: any = await container.load(entryUrl)
+      const result: any = await container.transform(loadResult.code, entryUrl)
+      expect(result.code).equals('2')
+    })
+  })
 })
 
 async function getPluginContainer(

packages/vite/src/node/server/pluginContainer.ts

@@ -42,9 +42,11 @@ import type {
   LoadResult,
   MinimalPluginContext,
   ModuleInfo,
+  ModuleOptions,
   NormalizedInputOptions,
   OutputOptions,
   ParallelPluginHooks,
+  PartialNull,
   PartialResolvedId,
   ResolvedId,
   RollupError,
@@ -126,8 +128,6 @@ export interface PluginContainer {
 
 type PluginContext = Omit<
   RollupPluginContext,
-  // not supported
-  | 'load'
   // not documented
   | 'cache'
   // deprecated
@@ -221,6 +221,10 @@ export async function createPluginContainer(
       if (key in info) {
         return info[key]
       }
+      // Don't throw an error when returning from an async function
+      if (key === 'then') {
+        return undefined
+      }
       throw Error(
         `[vite] The "${key}" property of ModuleInfo is not supported.`,
       )
@@ -306,6 +310,28 @@ export async function createPluginContainer(
       return out as ResolvedId | null
     }
 
+    async load(
+      options: {
+        id: string
+        resolveDependencies?: boolean
+      } & Partial<PartialNull<ModuleOptions>>,
+    ): Promise<ModuleInfo> {
+      // We may not have added this to our module graph yet, so ensure it exists
+      await moduleGraph?.ensureEntryFromUrl(options.id)
+      // Not all options passed to this function make sense in the context of loading individual files,
+      // but we can at least update the module info properties we support
+      updateModuleInfo(options.id, options)
+
+      await container.load(options.id)
+      const moduleInfo = this.getModuleInfo(options.id)
+      // This shouldn't happen due to calling ensureEntryFromUrl, but 1) our types can't ensure that
+      // and 2) moduleGraph may not have been provided (though in the situations where that happens,
+      // we should never have plugins calling this.load)
+      if (!moduleInfo)
+        throw Error(`Failed to load module with id ${options.id}`)
+      return moduleInfo
+    }
+
     getModuleInfo(id: string) {
       return getModuleInfo(id)
     }