feat(feature-detector): introduces edge signature detection

.changeset/kind-falcons-jump.md

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+---
+'@edge-runtime/feature-detector': patch
+---
+
+introduce hasEdgeSignature detection utility

docs/pages/packages/_meta.json

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 {
   "cookies": "@edge-runtime/cookies",
+  "feature-detector": "@edge-runtime/feature-detector",
   "format": "@edge-runtime/format",
   "jest-environment": "@edge-runtime/jest-environment",
   "jest-expect": "@edge-runtime/jest-expect",

docs/pages/packages/feature-detector.mdx

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+import { Callout } from 'nextra-theme-docs'
+import { Tabs, Tab } from '../../components/tabs'
+
+# Edge Runtime Code analysis utilities
+
+The **@edge-runtime/feature-detector** package contains utilities to analyze code running on the edge and its used low-level APIs.
+
+It leverages the excellent [ts-morph](https://ts-morph.com/) package, which is a wrapper around TypeScript compiler API to navigate its Abstract Syntaxt Tree (AST).
+
+It can analyse JavaScript and TypeScript code.
+
+<Callout type='warning' emoji='⚠️'>
+  Please note this is an alpha version.
+</Callout>
+
+## Installation
+
+<Tabs items={['npm', 'yarn', 'pnpm']} storageKey='selected-pkg-manager'>
+  <Tab>```sh npm install @edge-runtime/feature-detector --save ```</Tab>
+  <Tab>```sh yarn add @edge-runtime/feature-detector ```</Tab>
+  <Tab>```sh pnpm install @edge-runtime/feature-detector --save ```</Tab>
+</Tabs>
+
+This package includes built-in TypeScript support.
+
+## Usage
+
+Here is an example of checking whether a file's default export is a function matching the edge signature, such as:
+
+```js
+export default function () {
+  return Response.json({ message: 'hello world!' })
+}
+```
+
+```ts
+import { hasEdgeSignature } from '@edge-runtime/feature-detector'
+
+const sourceFilePath = './test.js' // could be TypeScript as well. Must be in current working directory
+
+if (hasEdgeSignature(sourceFilePath)) {
+  console.log(`${sourcefilePath} can run on the edge``)
+}
+```
+
+## API
+
+<Callout type='warning' emoji='⚠️'>
+  Work in progress
+</Callout>

packages/feature-detector/README.md

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+<div align="center">
+  <br>
+  <img src="https://edge-runtime.vercel.app/og-image.png" alt="edge-runtime logo">
+  <br>
+  <br>
+  <p align="center"><strong>@edge-runtime/feature-detector</strong>: utilities to analyze code running on the edge and its used low-level APIs.</p>
+  <p align="center">See <a href="https://edge-runtime.vercel.app/packages/feature-detector" target='_blank' rel='noopener noreferrer'>@edge-runtime/feature-detector</a> section in our <a href="https://edge-runtime.vercel.app/" target='_blank' rel='noopener noreferrer'>website</a> for more information.</p>
+  <br>
+</div>
+
+## Install
+
+**Note: this is an alpha version.**
+
+Using npm:
+
+```sh
+npm install @edge-runtime/feature-detector --save
+```
+
+or using yarn:
+
+```sh
+yarn add @edge-runtime/feature-detector --dev
+```
+
+or using pnpm:
+
+```sh
+pnpm install @edge-runtime/feature-detector --save
+```
+
+## License
+
+**@edge-runtime/feature-detector** © [Vercel](https://vercel.com), released under the [MPLv2](https://github.com/vercel/edge-runtime/blob/main/LICENSE.md) License.<br>
+Authored and maintained by [Vercel](https://vercel.com) with help from [contributors](https://github.com/vercel/edge-runtime/contributors).
+
+> [vercel.com](https://vercel.com) · GitHub [Vercel](https://github.com/vercel) · Twitter [@vercel](https://twitter.com/vercel)

packages/feature-detector/jest.config.ts

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+import buildConfig from '../../jest.config'
+import type { Config } from '@jest/types'
+
+const config: Config.InitialOptions = buildConfig(__dirname)
+config.transform!['\\.txt$'] = 'jest-text-transformer'
+export default config

packages/feature-detector/package.json

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+{
+  "name": "@edge-runtime/feature-detector",
+  "description": "Helpers for analyzing code running on the edge and its used low-level APIs",
+  "homepage": "https://edge-runtime.vercel.app/packages/feature-detector",
+  "version": "1.0.0-alpha.1",
+  "main": "dist/index.js",
+  "module": "dist/index.mjs",
+  "repository": {
+    "directory": "packages/feature-detector",
+    "type": "git",
+    "url": "git+https://github.com/vercel/edge-runtime.git"
+  },
+  "bugs": {
+    "url": "https://github.com/vercel/edge-runtime/issues"
+  },
+  "keywords": [],
+  "devDependencies": {
+    "jest-text-transformer": "1.0.4",
+    "next": "^13.1.1",
+    "react": "~18.2.0",
+    "react-dom": "~18.2.0",
+    "tsup": "^6"
+  },
+  "scripts": {
+    "build": "pnpm run build:patch && pnpm run build:src",
+    "build:patch": "ts-node scripts/patch-type-definition.ts",
+    "build:src": "tsup",
+    "clean:build": "rm -rf dist",
+    "prebuild": "pnpm run clean:build",
+    "test": "jest"
+  },
+  "license": "MPLv2",
+  "publishConfig": {
+    "access": "public"
+  },
+  "types": "dist/index.d.ts",
+  "dependencies": {
+    "ts-morph": "^17.0.1"
+  }
+}

packages/feature-detector/scripts/patch-type-definition.ts

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+// assumes being ran in packages/feature-detector
+
+import { get } from 'node:https'
+import { writeFile } from 'node:fs/promises'
+import { join } from 'node:path'
+
+const repositoryBaseUrl =
+  'https://raw.githubusercontent.com/microsoft/TypeScript/main/lib'
+const destinationFile = join('src', 'utils/type-definition.txt')
+
+async function writeTypeDefinition() {
+  const aggregatedContent = await fetchTypeDefinitions([
+    'lib.es2022.d.ts',
+    'lib.dom.d.ts',
+  ])
+  await writeFile(destinationFile, patchContent(aggregatedContent).join('\n'))
+}
+
+async function fetchTypeDefinitions(files: string[]) {
+  const result = []
+  for (const file of files) {
+    result.push(...(await fetchTypeDefinition(file)))
+  }
+  return result
+}
+
+async function fetchTypeDefinition(file: string): Promise<string[]> {
+  // I wish we could use node@18's fetch...
+  const content = await new Promise<string>((resolve, reject) =>
+    get(`${repositoryBaseUrl}/${file}`, (response) => {
+      let content = ''
+      response.setEncoding('utf8')
+      response.on('data', (chunk: string) => (content += chunk))
+      response.once('end', () => resolve(content))
+      response.once('error', reject)
+    })
+  )
+  const result = []
+  for (const line of content.split('\n')) {
+    const reference = hasReference(line)
+    if (reference) {
+      result.push(...(await fetchTypeDefinition(`lib.${reference}.d.ts`)))
+    } else {
+      result.push(line)
+    }
+  }
+  return result
+}
+
+function hasReference(line: string) {
+  const match = line.match(/^\/\/\/\s*<reference\s+lib\s*=\s*"(.+)"\s*\/>/)
+  return match ? match[1] : null
+}
+
+function patchContent(lines: string[]) {
+  const result = []
+  let inComment = false
+  for (const line of lines) {
+    if (inComment) {
+      if (isMultiCommentEnd(line)) {
+        inComment = false
+      }
+    } else {
+      if (isMultiCommentStart(line)) {
+        inComment = true
+      } else if (!isSingleComment(line) && !isBlankLine(line)) {
+        result.push(...applyPatch(line))
+      }
+    }
+  }
+  return result
+}
+
+function applyPatch(line: string) {
+  if (line === 'declare var Response: {') {
+    // adding missing json static method
+    // https://fetch.spec.whatwg.org/#response-class
+    return [line, '    json(data?: any, init?: ResponseInit): Response;']
+  }
+  return [line]
+}
+
+function isMultiCommentStart(line: string) {
+  return /^\s*\/\*.*(?<!\*\/\s*)$/.test(line)
+}
+
+function isMultiCommentEnd(line: string) {
+  return /\*\/\s*$/.test(line)
+}
+
+function isSingleComment(line: string) {
+  return /^(?!\s*\/\/\/ <r)\s*\/\/|^\s*\/\*.+\*\//.test(line)
+}
+
+function isBlankLine(line: string) {
+  return /^\s*$/.test(line)
+}
+
+writeTypeDefinition()
+  .then((content) => {
+    process.exit(0)
+  })
+  .catch((error) => {
+    console.log('Errored', error)
+    process.exit(1)
+  })

packages/feature-detector/src/has-edge-signature.ts

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+import { Project } from 'ts-morph'
+import { getDefaultExport } from './utils/exports'
+import { getReturnType } from './utils/functions'
+import { buildProject } from './utils/project'
+import { extractFromPromise, isSubClassOf } from './utils/types'
+
+/**
+ * Returns true if the default export of the provided file is a function returning a web Response object.
+ */
+export function hasEdgeSignature(
+  sourcePath: string,
+  project: Project = buildProject()
+) {
+  const sourceFile = project.addSourceFileAtPath(sourcePath)
+  const defaultExport = getDefaultExport(sourceFile)
+  if (!defaultExport) {
+    return false
+  }
+  const returnType = getReturnType(defaultExport)
+  if (!returnType) {
+    return false
+  }
+  return isSubClassOf(extractFromPromise(returnType), 'Response')
+}

packages/feature-detector/src/index.ts

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+export * from './has-edge-signature'

packages/feature-detector/src/utils/exports.ts

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+import { Node, SourceFile } from 'ts-morph'
+
+/**
+ * Get the default export of a modules, if any.
+ * Supported:
+ * - export definition: `export default function foo() {}`
+ * - exported declaration: `const foo = 'bar'; export default foo`
+ */
+export function getDefaultExport(sourceFile: SourceFile): Node | undefined {
+  const defaultExport = sourceFile.getDefaultExportSymbol()
+  return (
+    defaultExport?.getValueDeclaration() ??
+    defaultExport?.getDeclarations()?.[0] // when exporting a variable: `export default handler`
+  )
+}

packages/feature-detector/src/utils/functions.ts

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+import { Node, SyntaxKind, Type } from 'ts-morph'
+
+const { ExportAssignment, Identifier, FunctionDeclaration, ArrowFunction } =
+  SyntaxKind
+
+/**
+ * Exteracts the return type of a function, if any.
+ * Supports:
+ * - function declaration `function foo() {}`
+ * - function expression `const foo = function() {}`
+ * - arrow functions `const foo = () => {}`
+ * - module exports
+ */
+export function getReturnType(node?: Node): Type | undefined {
+  switch (node?.getKind()) {
+    case ExportAssignment:
+      return getReturnType(node.asKind(ExportAssignment)?.getExpression())
+    case Identifier:
+      return getReturnType(node.getSymbol()?.getValueDeclaration())
+    case FunctionDeclaration:
+      return node.asKind(FunctionDeclaration)?.getReturnType()
+    case ArrowFunction:
+      return node.asKind(ArrowFunction)?.getReturnType()
+  }
+}

packages/feature-detector/src/utils/project.ts

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+import { Project } from 'ts-morph'
+// @ts-ignore will be resolved by tsup & jest
+import typeDefinitionContent from './type-definition.txt'
+
+/**
+ * Builds a TS-morph project that allows JS code and loads our custom Response + Promise types
+ */
+export function buildProject() {
+  const project = new Project({
+    compilerOptions: {
+      allowJs: true,
+    },
+  })
+  project.createSourceFile('node_modules/index.d.ts', typeDefinitionContent)
+  project.addDirectoryAtPathIfExists('.')
+  return project
+}