perf(build): enable unsafe fast drop in non-watch mode (#6404)

Author: chenjiahan

packages/core/src/cli/commands.ts

@@ -123,6 +123,10 @@ export function setupCommands(): void {
     )
     .action(async (options: BuildOptions) => {
       try {
+        if (!options.watch) {
+          process.env.RSPACK_UNSAFE_FAST_DROP = 'true';
+        }
+
         const rsbuild = await init({
           cliOptions: options,
           isBuildWatch: options.watch,

packages/core/src/env.d.ts

@@ -11,3 +11,12 @@ declare global {
   const RSBUILD_WEB_SOCKET_TOKEN: string;
   const Deno: unknown;
 }
+
+declare namespace NodeJS {
+  interface ProcessEnv {
+    /**
+     * @experimental
+     */
+    RSPACK_UNSAFE_FAST_DROP?: string;
+  }
+}

packages/core/src/provider/createCompiler.ts

@@ -105,6 +105,11 @@ export async function createCompiler(options: InitConfigsOptions): Promise<{
     ? rspack(rspackConfigs)
     : rspack(rspackConfigs[0]);
 
+  // Enable unsafe fast drop in non-watch mode to improve performance
+  if (process.env.RSPACK_UNSAFE_FAST_DROP === 'true') {
+    compiler.unsafeFastDrop = true;
+  }
+
   let isVersionLogged = false;
   let isCompiling = false;