fix(hmr): trigger prune event when last import is removed (#20781)

packages/vite/src/node/plugins/importAnalysis.ts

@@ -299,7 +299,17 @@ export function importAnalysisPlugin(config: ResolvedConfig): Plugin {
         !imports.length &&
         !(this as unknown as TransformPluginContext)._addedImports
       ) {
-        importerModule.isSelfAccepting = false
+        const prunedImports = await moduleGraph.updateModuleInfo(
+          importerModule,
+          new Set(),
+          null,
+          new Set(),
+          null,
+          false,
+        )
+        if (prunedImports) {
+          handlePrunedModules(prunedImports, environment)
+        }
         debug?.(
           `${timeFrom(msAtStart)} ${colors.dim(
             `[no imports] ${prettifyUrl(importer, root)}`,

playground/hmr/__tests__/hmr.spec.ts

@@ -1022,9 +1022,17 @@ if (!isBuild) {
     editFile('prune/dep1.js', (code) =>
       code.replace(`import './dep2.js'`, `// import './dep2.js'`),
     )
+    // Prune is triggered when there are other dependencies.
     await expect
       .poll(() => page.textContent('.prune'))
       .toMatch('prune-init|dep2-disposed|dep2-pruned')
+    editFile('prune/dep1.js', (code) =>
+      code.replace(`import './dep3.js'`, `// import './dep3.js'`),
+    )
+    // Prune is triggered when there are no more dependencies.
+    await expect
+      .poll(() => page.textContent('.prune'))
+      .toMatch('prune-init|dep2-disposed|dep2-pruned|dep3-disposed|dep3-pruned')
   })
 
   test('import.meta.hot?.accept', async () => {

playground/hmr/prune/dep1.js

@@ -1,8 +1,2 @@
 import './dep2.js'
-
-// TODO: https://github.com/vitejs/vite/issues/20781
-// currently we need one more `import` in this module
-// to trigger prune for depending module `dep2.js` since
-// the prune event logic is skipped when `es-module-lexer`
-// detects `imports.length === 0`
-import './dep2-other.js'
+import './dep3.js'

playground/hmr/prune/dep3.js

@@ -0,0 +1,8 @@
+if (import.meta.hot) {
+  import.meta.hot.dispose(() => {
+    document.querySelector('.prune').textContent += '|dep3-disposed'
+  })
+  import.meta.hot.prune(() => {
+    document.querySelector('.prune').textContent += '|dep3-pruned'
+  })
+}