feat: size impact analysis

app/bundler/events.ts

@@ -0,0 +1,6 @@
+import type { ProgressMessage } from './types'
+
+/**
+ * emitted during package initialization and bundling.
+ */
+export const progress = createEventHook<ProgressMessage>()

app/bundler/lib/bundler.ts

@@ -0,0 +1,257 @@
+import { encodeUtf8, getUtf8Length } from '@atcute/uint8array'
+import * as zstd from '@bokuweb/zstd-wasm'
+import { rolldown } from '@rolldown/browser'
+import { memfs } from '@rolldown/browser/experimental'
+
+import { progress } from '../events'
+import type { BundleChunk, BundleOptions, BundleResult } from '../types'
+
+import { BundleError } from './errors'
+import { analyzeModule } from './module-type'
+
+const { volume } = memfs!
+
+// #region helpers
+
+const VIRTUAL_ENTRY_ID = '\0virtual:entry'
+
+/**
+ * get compressed size using a compression stream.
+ */
+async function getCompressedSize(code: string, format: CompressionFormat): Promise<number> {
+  const { readable, writable } = new CompressionStream(format)
+
+  {
+    const writer = writable.getWriter()
+    writer.write(encodeUtf8(code))
+    writer.close()
+  }
+
+  let size = 0
+  {
+    const reader = readable.getReader()
+    while (true) {
+      // oxlint-disable-next-line no-await-in-loop
+      const { done, value: chunk } = await reader.read()
+      if (done) {
+        break
+      }
+
+      size += chunk.byteLength
+    }
+  }
+
+  return size
+}
+
+/**
+ * get gzip size using compression stream.
+ */
+function getGzipSize(code: string): Promise<number> {
+  return getCompressedSize(code, 'gzip')
+}
+
+/**
+ * whether brotli compression is supported.
+ * - `undefined`: not yet checked
+ * - `true`: supported
+ * - `false`: not supported
+ */
+let isBrotliSupported: boolean | undefined
+
+/**
+ * get brotli size using compression stream, if supported.
+ * returns `undefined` if brotli is not supported by the browser.
+ */
+async function getBrotliSize(code: string): Promise<number | undefined> {
+  if (isBrotliSupported === false) {
+    return undefined
+  }
+
+  if (isBrotliSupported === undefined) {
+    try {
+      // @ts-expect-error 'brotli' is not in the type definition yet
+      const size = await getCompressedSize(code, 'brotli')
+      isBrotliSupported = true
+      return size
+    } catch {
+      isBrotliSupported = false
+      return undefined
+    }
+  }
+
+  // @ts-expect-error 'brotli' is not in the type definition yet
+  return getCompressedSize(code, 'brotli')
+}
+
+/**
+ * get zstd-compressed size using WASM.
+ */
+function getZstdSize(code: string): number {
+  const encoded = encodeUtf8(code)
+  const compressed = zstd.compress(encoded)
+  return compressed.byteLength
+}
+
+// #endregion
+
+// #region core
+
+/**
+ * bundles a subpath from a package that's already loaded in rolldown's memfs.
+ *
+ * @param packageName the package name (e.g., "react")
+ * @param subpath the export subpath to bundle (e.g., ".", "./utils")
+ * @param selectedExports specific exports to include, or null for all
+ * @param options bundling options
+ * @returns bundle result with chunks, sizes, and exported names
+ */
+export async function bundlePackage(
+  packageName: string,
+  subpath: string,
+  selectedExports: string[] | null,
+  options: BundleOptions,
+): Promise<BundleResult> {
+  // track whether module is CJS (set in load hook)
+  let isCjs = false
+
+  // bundle with rolldown
+  const bundle = await rolldown({
+    input: { main: VIRTUAL_ENTRY_ID },
+    cwd: '/',
+    external: options.rolldown?.external,
+    plugins: [
+      {
+        name: 'virtual-entry',
+        resolveId(id: string) {
+          if (id === VIRTUAL_ENTRY_ID) {
+            return id
+          }
+        },
+        async load(id: string) {
+          if (id !== VIRTUAL_ENTRY_ID) {
+            return
+          }
+
+          const importPath = subpath === '.' ? packageName : `${packageName}${subpath.slice(1)}`
+
+          // resolve the entry module
+          const resolved = await this.resolve(importPath)
+          if (!resolved) {
+            throw new BundleError(`failed to resolve entry module: ${importPath}`)
+          }
+
+          // JSON files only have a default export
+          if (resolved.id.endsWith('.json')) {
+            return `export { default } from '${importPath}';\n`
+          }
+
+          // read the source file
+          let source: string
+          try {
+            source = volume.readFileSync(resolved.id, 'utf8') as string
+          } catch {
+            throw new BundleError(`failed to read entry module: ${resolved.id}`)
+          }
+
+          // parse and analyze the module
+          let ast
+          try {
+            ast = this.parse(source)
+          } catch {
+            throw new BundleError(`failed to parse entry module: ${resolved.id}`)
+          }
+
+          const moduleInfo = analyzeModule(ast)
+          isCjs = moduleInfo.type === 'cjs'
+
+          // CJS modules can't be tree-shaken effectively, just re-export default
+          if (moduleInfo.type === 'cjs') {
+            return `export { default } from '${importPath}';\n`
+          }
+
+          // unknown/side-effects only modules have no exports
+          if (moduleInfo.type === 'unknown') {
+            return `export {} from '${importPath}';\n`
+          }
+
+          // ESM module handling
+          if (selectedExports === null) {
+            // re-export everything
+            let code = `export * from '${importPath}';\n`
+            if (moduleInfo.hasDefaultExport) {
+              code += `export { default } from '${importPath}';\n`
+            }
+            return code
+          }
+
+          // specific exports selected (empty array = export nothing)
+          // quote names to handle non-identifier exports
+          const quoted = selectedExports.map(e => JSON.stringify(e))
+          return `export { ${quoted.join(', ')} } from '${importPath}';\n`
+        },
+      },
+    ],
+  })
+
+  const output = await bundle.generate({
+    format: 'esm',
+    minify: options.rolldown?.minify ?? true,
+  })
+
+  // process all chunks
+  const rawChunks = output.output.filter(o => o.type === 'chunk')
+
+  progress.trigger({ type: 'progress', kind: 'compress' })
+
+  const chunks: BundleChunk[] = await Promise.all(
+    rawChunks.map(async chunk => {
+      const code = chunk.code
+      const size = getUtf8Length(code)
+      const [gzipSize, brotliSize, zstdSize] = await Promise.all([
+        getGzipSize(code),
+        getBrotliSize(code),
+        getZstdSize(code),
+      ])
+
+      return {
+        fileName: chunk.fileName,
+        code,
+        size,
+        gzipSize,
+        brotliSize,
+        zstdSize,
+        isEntry: chunk.isEntry,
+        exports: chunk.exports || [],
+      }
+    }),
+  )
+
+  // find entry chunk for exports
+  const entryChunk = chunks.find(c => c.isEntry)
+  if (!entryChunk) {
+    throw new BundleError('no entry chunk found in bundle output')
+  }
+
+  // aggregate sizes
+  const totalSize = chunks.reduce((acc, c) => acc + c.size, 0)
+  const totalGzipSize = chunks.reduce((acc, c) => acc + c.gzipSize, 0)
+  const totalBrotliSize = isBrotliSupported
+    ? chunks.reduce((acc, c) => acc + c.brotliSize!, 0)
+    : undefined
+  const totalZstdSize = chunks.reduce((acc, c) => acc + c.zstdSize!, 0)
+
+  await bundle.close()
+
+  return {
+    chunks,
+    size: totalSize,
+    gzipSize: totalGzipSize,
+    brotliSize: totalBrotliSize,
+    zstdSize: totalZstdSize,
+    exports: entryChunk.exports,
+    isCjs,
+  }
+}
+
+// #endregion

app/bundler/lib/errors.ts

@@ -0,0 +1,81 @@
+/**
+ * base class for all teardown errors.
+ */
+export class TeardownError extends Error {
+  constructor(message: string) {
+    super(message)
+    this.name = 'TeardownError'
+  }
+}
+
+/**
+ * thrown when a package cannot be found in the registry.
+ */
+export class PackageNotFoundError extends TeardownError {
+  readonly packageName: string
+  readonly registry: string
+
+  constructor(packageName: string, registry: string) {
+    super(`package not found: ${packageName}`)
+    this.name = 'PackageNotFoundError'
+    this.packageName = packageName
+    this.registry = registry
+  }
+}
+
+/**
+ * thrown when no version of a package satisfies the requested range.
+ */
+export class NoMatchingVersionError extends TeardownError {
+  readonly packageName: string
+  readonly range: string
+
+  constructor(packageName: string, range: string) {
+    super(`no version of ${packageName} satisfies ${range}`)
+    this.name = 'NoMatchingVersionError'
+    this.packageName = packageName
+    this.range = range
+  }
+}
+
+/**
+ * thrown when a package specifier is malformed.
+ */
+export class InvalidSpecifierError extends TeardownError {
+  readonly specifier: string
+
+  constructor(specifier: string, reason?: string) {
+    super(
+      reason ? `invalid specifier: ${specifier} (${reason})` : `invalid specifier: ${specifier}`,
+    )
+    this.name = 'InvalidSpecifierError'
+    this.specifier = specifier
+  }
+}
+
+/**
+ * thrown when a network request fails.
+ */
+export class FetchError extends TeardownError {
+  readonly url: string
+  readonly status: number
+  readonly statusText: string
+
+  constructor(url: string, status: number, statusText: string) {
+    super(`fetch failed: ${status} ${statusText}`)
+    this.name = 'FetchError'
+    this.url = url
+    this.status = status
+    this.statusText = statusText
+  }
+}
+
+/**
+ * thrown when bundling fails.
+ */
+export class BundleError extends TeardownError {
+  constructor(message: string) {
+    super(message)
+    this.name = 'BundleError'
+  }
+}