feat: add --metafile flag, closes #443

docs/README.md

@@ -33,6 +33,7 @@ tsup src/index.ts src/cli.ts
 ```
 
 This will output `dist/index.js` and `dist/cli.js`.
+
 ### Excluding packages
 
 By default tsup bundles all `import`-ed modules but `dependencies` and `peerDependencies` in your `packages.json` are always excluded, you can also use `--external <module>` flag to mark other packages as external.
@@ -63,7 +64,7 @@ You can use any of these files:
 - `tsup.config.json`
 - `tsup` property in your `package.json`
 
-> In all the custom files you can export the options either as `tsup`, `default` or `module.exports =` 
+> In all the custom files you can export the options either as `tsup`, `default` or `module.exports =`
 
 #### TypeScript
 
@@ -109,7 +110,6 @@ module.exports = {
 }
 ```
 
-
 ### Generate declaration file
 
 ```bash
@@ -277,6 +277,12 @@ module.exports = {
 }
 ```
 
+### Metafile
+
+Passing `--metafile` flag to tell esbuild to produce some metadata about the build in JSON format. You can feed the output file to analysis tools like [bundle buddy](https://www.bundle-buddy.com/esbuild) to visualize the modules in your bundle and how much space each one takes up.
+
+The file outputs as `metafile-{format}.json`, e.g. `tsup --format cjs,esm` will generate `metafile-cjs.json` and `metafile-esm.json`.
+
 ---
 
 For more details:

src/cli-main.ts

@@ -76,6 +76,7 @@ export async function main(options: Options = {}) {
       'Supress non-error logs (excluding "onSuccess" process output)'
     )
     .option('--pure <express>', 'Mark specific expressions as pure')
+    .option('--metafile', 'Emit esbuild metafile (a JSON file)')
     .action(async (files: string[], flags) => {
       const { build } = await import('.')
       Object.assign(options, {

src/index.ts

@@ -111,6 +111,11 @@ export type Options = {
    * @see https://esbuild.github.io/api/#inject
    */
   inject?: string[]
+  /**
+   * Emit esbuild metafile
+   * @see https://esbuild.github.io/api/#metafile
+   */
+  metafile?: boolean
 }
 
 export type NormalizedOptions = MarkRequired<
@@ -233,6 +238,7 @@ export async function runEsbuild(
       keepNames: options.keepNames,
       incremental: !!options.watch,
       pure: typeof options.pure === 'string' ? [options.pure] : options.pure,
+      metafile: Boolean(options.metafile),
     })
   } catch (error) {
     log(format, 'error', 'Build failed')
@@ -328,6 +334,16 @@ export async function runEsbuild(
     )
   }
 
+  if (options.metafile && result?.metafile) {
+    const outPath = path.resolve(outDir, `metafile-${format}.json`)
+    await fs.promises.mkdir(path.dirname(outPath), { recursive: true })
+    await fs.promises.writeFile(
+      outPath,
+      JSON.stringify(result.metafile),
+      'utf8'
+    )
+  }
+
   return result
 }
 

test/index.test.ts

@@ -1014,3 +1014,19 @@ test('declaration files with multiple entrypoints #316', async () => {
     "
   `)
 })
+
+test('esbuild metafile', async () => {
+  const { outFiles } = await run(
+    getTestName(),
+    { 'input.ts': `export const foo = 1` },
+    {
+      flags: ['--metafile'],
+    }
+  )
+  expect(outFiles).toMatchInlineSnapshot(`
+    Array [
+      "input.js",
+      "metafile-cjs.json",
+    ]
+  `)
+})