esm: update loaders warning

PR-URL: #49633 Backport-PR-URL: #50669 Reviewed-By: Jacob Smith <[email protected]> Reviewed-By: Benjamin Gruenbaum <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Guy Bedford <[email protected]>

Author: GeoffreyBooth

lib/internal/modules/esm/loader.js

@@ -4,9 +4,16 @@
 require('internal/modules/cjs/loader');
 
 const{
+ ArrayPrototypeJoin,
+ ArrayPrototypeMap,
+ ArrayPrototypeReduce,
  FunctionPrototypeCall,
+ JSONStringify,
  ObjectSetPrototypeOf,
+ RegExpPrototypeSymbolReplace,
  SafeWeakMap,
+ encodeURIComponent,
+ hardenRegExp,
 }=primordials;
 
 const{
@@ -486,7 +493,7 @@ class CustomizedModuleLoader{
 }
 }
 
-letemittedExperimentalWarning=false;
+letemittedLoaderFlagWarning=false;
 /**
  * A loader instance is used as the main entry point for loading ES modules. Currently, this is a singleton; there is
  * only one used for loading the main module and everything in its dependency graph, though separate instances of this
@@ -502,9 +509,24 @@ function createModuleLoader(useCustomLoadersIfPresent = true){
 !require('internal/modules/esm/utils').isLoaderWorker()){
 constuserLoaderPaths=getOptionValue('--experimental-loader');
 if(userLoaderPaths.length>0){
-if(!emittedExperimentalWarning){
-emitExperimentalWarning('Custom ESM Loaders');
-emittedExperimentalWarning=true;
+if(!emittedLoaderFlagWarning){
+constreadableURIEncode=(string)=>ArrayPrototypeReduce(
+[
+[/'/g,'%27'],// We need to URL-encode the single quote as it's the delimiter for the --import flag.
+[/%22/g,'"'],// We can decode the double quotes to improve readability.
+[/%2F/ig,'/'],// We can decode the slashes to improve readability.
+],
+(str,{0: regex,1: replacement})=>RegExpPrototypeSymbolReplace(hardenRegExp(regex),str,replacement),
+encodeURIComponent(string));
+process.emitWarning(
+'`--experimental-loader` may be removed in the future; instead use `register()`:\n'+
+`--import 'data:text/javascript,import{register } from "node:module" import{pathToFileURL } from "node:url" ${ArrayPrototypeJoin(
+ArrayPrototypeMap(userLoaderPaths,(loader)=>`register(${readableURIEncode(JSONStringify(loader))}, pathToFileURL("./"))`),
+' ',
+)};'`,
+'ExperimentalWarning',
+);
+emittedLoaderFlagWarning=true;
 }
 customizations=newCustomizedModuleLoader();
 }

test/es-module/test-esm-experimental-warnings.mjs

@@ -24,15 +24,19 @@ describe('ESM: warn for obsolete hooks provided',{concurrency: true }, () =>{
 
 describe('experimental warnings for enabled experimental feature',()=>{
 for(
-const[experiment,arg]of[
-[/CustomESMLoaders/,`--experimental-loader=${fileURL('es-module-loaders','hooks-custom.mjs')}`],
+const[experiment, ...args]of[
+[
+/`--experimental-loader`mayberemovedinthefuture/,
+'--experimental-loader',
+fileURL('es-module-loaders','hooks-custom.mjs'),
+],
 [/NetworkImports/,'--experimental-network-imports'],
 [/specifierresolution/,'--experimental-specifier-resolution=node'],
 ]
 ){
 it(`should print for ${experiment.toString().replaceAll('/','')}`,async()=>{
 const{ code, signal, stderr }=awaitspawnPromisified(execPath,[
-arg,
+...args,
 '--input-type=module',
 '--eval',
 `import ${JSON.stringify(fileURL('es-module-loaders','module-named-exports.mjs'))}`,