Change the Server Actions feature flag to be validated at compile time

packages/next-swc/crates/core/src/server_actions.rs

@@ -22,6 +22,7 @@ use turbopack_binding::swc::core::{
 #[serde(deny_unknown_fields, rename_all = "camelCase")]
 pub struct Config {
     pub is_server: bool,
+    pub enabled: bool
 }
 
 pub fn server_actions<C: Comments>(
@@ -101,6 +102,7 @@ impl<C: Comments> ServerActions<C> {
                     &mut body.stmts,
                     remove_directive,
                     &mut is_action_fn,
+                    self.config.enabled,
                 );
 
                 if is_action_fn && !self.config.is_server {
@@ -721,6 +723,7 @@ impl<C: Comments> VisitMut for ServerActions<C> {
             stmts,
             &mut self.in_action_file,
             &mut self.has_action,
+            self.config.enabled,
         );
 
         let old_annotations = self.annotations.take();
@@ -1231,6 +1234,7 @@ fn remove_server_directive_index_in_module(
     stmts: &mut Vec<ModuleItem>,
     in_action_file: &mut bool,
     has_action: &mut bool,
+    enabled: bool,
 ) {
     let mut is_directive = true;
 
@@ -1244,6 +1248,16 @@ fn remove_server_directive_index_in_module(
                     if is_directive {
                         *in_action_file = true;
                         *has_action = true;
+                        if !enabled {
+                            HANDLER.with(|handler| {
+                                handler
+                                    .struct_span_err(
+                                        *span,
+                                        "To use Server Actions, please enable the feature flag in your Next.js config. Read more: https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions#convention",
+                                    )
+                                    .emit()
+                            });
+                        }
                         return false;
                     } else {
                         HANDLER.with(|handler| {
@@ -1320,6 +1334,7 @@ fn remove_server_directive_index_in_fn(
     stmts: &mut Vec<Stmt>,
     remove_directive: bool,
     is_action_fn: &mut bool,
+    enabled: bool,
 ) {
     let mut is_directive = true;
 
@@ -1332,6 +1347,16 @@ fn remove_server_directive_index_in_fn(
             if value == "use server" {
                 if is_directive {
                     *is_action_fn = true;
+                    if !enabled {
+                        HANDLER.with(|handler| {
+                            handler
+                                .struct_span_err(
+                                    *span,
+                                    "To use Server Actions, please enable the feature flag in your Next.js config. Read more: https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions#convention",
+                                )
+                                .emit()
+                        });
+                    }
                     if remove_directive {
                         return false;
                     }

packages/next/src/build/swc/options.ts

@@ -43,6 +43,7 @@ function getBaseSWCOptions({
   swcCacheDir,
   isServerLayer,
   hasServerComponents,
+  isServerActionsEnabled,
 }: {
   filename: string
   jest?: boolean
@@ -57,6 +58,7 @@ function getBaseSWCOptions({
   swcCacheDir?: string
   isServerLayer?: boolean
   hasServerComponents?: boolean
+  isServerActionsEnabled?: boolean
 }) {
   const parserConfig = getParserOptions({ filename, jsConfig })
   const paths = jsConfig?.compilerOptions?.paths
@@ -157,6 +159,8 @@ function getBaseSWCOptions({
       : undefined,
     serverActions: hasServerComponents
       ? {
+          // TODO-APP: When Server Actions is stable, we need to remove this flag.
+          enabled: !!isServerActionsEnabled,
           isServer: !!isServerLayer,
         }
       : undefined,
@@ -285,6 +289,7 @@ export function getLoaderSWCOptions({
   relativeFilePathFromRoot,
   hasServerComponents,
   isServerLayer,
+  isServerActionsEnabled,
 }: // This is not passed yet as "paths" resolving is handled by webpack currently.
 // resolvedBaseUrl,
 {
@@ -304,6 +309,7 @@ export function getLoaderSWCOptions({
   relativeFilePathFromRoot: string
   hasServerComponents?: boolean
   isServerLayer: boolean
+  isServerActionsEnabled?: boolean
 }) {
   let baseOptions: any = getBaseSWCOptions({
     filename,
@@ -318,6 +324,7 @@ export function getLoaderSWCOptions({
     swcCacheDir,
     hasServerComponents,
     isServerLayer,
+    isServerActionsEnabled,
   })
   baseOptions.fontLoaders = {
     fontLoaders: [

packages/next/src/build/webpack/loaders/next-swc-loader.ts

@@ -73,6 +73,7 @@ async function loaderTransform(
     swcCacheDir,
     relativeFilePathFromRoot,
     hasServerComponents,
+    isServerActionsEnabled: nextConfig?.experimental?.serverActions,
     isServerLayer,
   })
 

packages/next/src/build/webpack/plugins/flight-client-entry-plugin.ts

@@ -350,21 +350,13 @@ export class FlightClientEntryPlugin {
       )
 
       if (actionEntryImports.size > 0) {
-        if (!this.useServerActions) {
-          compilation.errors.push(
-            new Error(
-              'Server Actions require `experimental.serverActions` option to be enabled in your Next.js config: https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions'
-            )
-          )
-        } else {
-          if (!actionMapsPerEntry[name]) {
-            actionMapsPerEntry[name] = new Map()
-          }
-          actionMapsPerEntry[name] = new Map([
-            ...actionMapsPerEntry[name],
-            ...actionEntryImports,
-          ])
+        if (!actionMapsPerEntry[name]) {
+          actionMapsPerEntry[name] = new Map()
         }
+        actionMapsPerEntry[name] = new Map([
+          ...actionMapsPerEntry[name],
+          ...actionEntryImports,
+        ])
       }
     })
 
@@ -388,31 +380,28 @@ export class FlightClientEntryPlugin {
       )
     }
 
-    compilation.hooks.finishModules.tapPromise(PLUGIN_NAME, () => {
-      const addedClientActionEntryList: Promise<any>[] = []
-      const actionMapsPerClientEntry: Record<string, Map<string, string[]>> = {}
-
-      // We need to create extra action entries that are created from the
-      // client layer.
-      // Start from each entry's created SSR dependency from our previous step.
-      for (const [name, ssrEntryDepdendencies] of Object.entries(
-        createdSSRDependenciesForEntry
-      )) {
-        // Collect from all entries, e.g. layout.js, page.js, loading.js, ...
-        // add agregate them.
-        const actionEntryImports = this.collectClientActionsFromDependencies({
-          compilation,
-          dependencies: ssrEntryDepdendencies,
-        })
+    if (this.useServerActions) {
+      compilation.hooks.finishModules.tapPromise(PLUGIN_NAME, () => {
+        const addedClientActionEntryList: Promise<any>[] = []
+        const actionMapsPerClientEntry: Record<
+          string,
+          Map<string, string[]>
+        > = {}
+
+        // We need to create extra action entries that are created from the
+        // client layer.
+        // Start from each entry's created SSR dependency from our previous step.
+        for (const [name, ssrEntryDepdendencies] of Object.entries(
+          createdSSRDependenciesForEntry
+        )) {
+          // Collect from all entries, e.g. layout.js, page.js, loading.js, ...
+          // add agregate them.
+          const actionEntryImports = this.collectClientActionsFromDependencies({
+            compilation,
+            dependencies: ssrEntryDepdendencies,
+          })
 
-        if (actionEntryImports.size > 0) {
-          if (!this.useServerActions) {
-            compilation.errors.push(
-              new Error(
-                'Server Actions require `experimental.serverActions` option to be enabled in your Next.js config: https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions'
-              )
-            )
-          } else {
+          if (actionEntryImports.size > 0) {
             if (!actionMapsPerClientEntry[name]) {
               actionMapsPerClientEntry[name] = new Map()
             }
@@ -422,47 +411,47 @@ export class FlightClientEntryPlugin {
             ])
           }
         }
-      }
 
-      for (const [name, actionEntryImports] of Object.entries(
-        actionMapsPerClientEntry
-      )) {
-        // If an action method is already created in the server layer, we don't
-        // need to create it again in the action layer.
-        // This is to avoid duplicate action instances and make sure the module
-        // state is shared.
-        let remainingClientImportedActions = false
-        const remainingActionEntryImports = new Map<string, string[]>()
-        for (const [dep, actionNames] of actionEntryImports) {
-          const remainingActionNames = []
-          for (const actionName of actionNames) {
-            const id = name + '@' + dep + '@' + actionName
-            if (!createdActions.has(id)) {
-              remainingActionNames.push(actionName)
+        for (const [name, actionEntryImports] of Object.entries(
+          actionMapsPerClientEntry
+        )) {
+          // If an action method is already created in the server layer, we don't
+          // need to create it again in the action layer.
+          // This is to avoid duplicate action instances and make sure the module
+          // state is shared.
+          let remainingClientImportedActions = false
+          const remainingActionEntryImports = new Map<string, string[]>()
+          for (const [dep, actionNames] of actionEntryImports) {
+            const remainingActionNames = []
+            for (const actionName of actionNames) {
+              const id = name + '@' + dep + '@' + actionName
+              if (!createdActions.has(id)) {
+                remainingActionNames.push(actionName)
+              }
+            }
+            if (remainingActionNames.length > 0) {
+              remainingActionEntryImports.set(dep, remainingActionNames)
+              remainingClientImportedActions = true
             }
           }
-          if (remainingActionNames.length > 0) {
-            remainingActionEntryImports.set(dep, remainingActionNames)
-            remainingClientImportedActions = true
-          }
-        }
 
-        if (remainingClientImportedActions) {
-          addedClientActionEntryList.push(
-            this.injectActionEntry({
-              compiler,
-              compilation,
-              actions: remainingActionEntryImports,
-              entryName: name,
-              bundlePath: name,
-              fromClient: true,
-            })
-          )
+          if (remainingClientImportedActions) {
+            addedClientActionEntryList.push(
+              this.injectActionEntry({
+                compiler,
+                compilation,
+                actions: remainingActionEntryImports,
+                entryName: name,
+                bundlePath: name,
+                fromClient: true,
+              })
+            )
+          }
         }
-      }
 
-      return Promise.all(addedClientActionEntryList)
-    })
+        return Promise.all(addedClientActionEntryList)
+      })
+    }
 
     // Invalidate in development to trigger recompilation
     const invalidator = getInvalidator(compiler.outputPath)

test/e2e/app-dir/actions/app-action-invalid.test.ts

@@ -34,7 +34,7 @@ createNextDescribe(
 
     it('should error if serverActions is not enabled', async () => {
       expect(next.cliOutput).toContain(
-        'Server Actions require `experimental.serverActions` option'
+        'To use Server Actions, please enable the feature flag in your Next.js config.'
       )
     })
   }