feat: warn user if config includes cjs format (#403)

Co-authored-by: Kevin Deng <[email protected]>

Author: Gugustinette

src/features/cjs.ts

@@ -0,0 +1,28 @@
+import coerce from 'semver/functions/coerce.js'
+import satisfies from 'semver/functions/satisfies.js'
+import type { ResolvedOptions } from '../options'
+
+/**
+ * If the config includes the `cjs` format and
+ * one of its target >= node 23.0.0 / 22.12.0,
+ * warn the user about the deprecation of CommonJS.
+ */
+export function warnLegacyCJS(config: ResolvedOptions): void {
+  if (!config.format.includes('cjs') || !config.target) {
+    return
+  }
+
+  const legacy = config.target.some((t) => {
+    const version = coerce(t.split('node')[1])
+    return version && satisfies(version, '>=23.0.0 || >=22.12.0')
+  })
+
+  if (legacy) {
+    config.logger.warnOnce(
+      'We recommend using the ESM format instead of CommonJS.\n' +
+        'The ESM format is compatible with modern platforms and runtimes, ' +
+        'and most new libraries are now distributed only in ESM format.\n' +
+        'Learn more at https://nodejs.org/en/learn/modules/publishing-a-package#how-did-we-get-here',
+    )
+  }
+}

src/index.ts

@@ -11,6 +11,7 @@ import {
 import { exec } from 'tinyexec'
 import treeKill from 'tree-kill'
 import { attw } from './features/attw'
+import { warnLegacyCJS } from './features/cjs'
 import { cleanOutDir } from './features/clean'
 import { copy } from './features/copy'
 import { writeExports, type TsdownChunks } from './features/exports'
@@ -103,6 +104,8 @@ export async function buildSingle(
 
   const { hooks, context } = await createHooks(config)
 
+  warnLegacyCJS(config)
+
   await rebuild(true)
   if (watch) {
     return () => rebuild()

src/utils/logger.ts

@@ -30,6 +30,8 @@ function format(msgs: any[]) {
   return msgs.filter((arg) => arg !== undefined && arg !== false).join(' ')
 }
 
+const warnedMessages = new Set<string>()
+
 export function createLogger(
   level: LogLevel = 'info',
   { customLogger, console = globalThis.console }: LoggerOptions = {},
@@ -46,8 +48,6 @@ export function createLogger(
     console[method](msg)
   }
 
-  const warnedMessages = new Set<string>()
-
   const logger: Logger = {
     level,