bun-macros

Bun 宏

Bun 宏会在打包时运行 JavaScript，并将结果内联到输出中。

快速入门

// src/config.ts (macro file)
export function getVersion() {
  return "1.0.0";
}

export function getBuildTime() {
  return new Date().toISOString();
}

// src/index.ts (consumer)
import { getVersion, getBuildTime } from "./config" with { type: "macro" };

// At bundle time, these become:
const version = "1.0.0";
const buildTime = "2024-01-15T12:00:00.000Z";

宏语法

// Import with macro attribute
import { fn } from "./macro-file" with { type: "macro" };

// Call the macro (evaluated at build time)
const result = fn();

常见用例

内联环境变量

// macros/env.ts
export function env(key: string): string {
  return process.env[key] ?? "";
}

// src/index.ts
import { env } from "./macros/env" with { type: "macro" };

const apiUrl = env("API_URL");
// Becomes: const apiUrl = "https://api.example.com";

Git 信息

// macros/git.ts
export function gitCommit(): string {
  return Bun.spawnSync(["git", "rev-parse", "HEAD"])
    .stdout.toString().trim();
}

export function gitBranch(): string {
  return Bun.spawnSync(["git", "branch", "--show-current"])
    .stdout.toString().trim();
}

// src/index.ts
import { gitCommit, gitBranch } from "./macros/git" with { type: "macro" };

const BUILD_INFO = {
  commit: gitCommit(),
  branch: gitBranch(),
};
// Inlined at build time

嵌入文件

// macros/embed.ts
export function embedFile(path: string): string {
  return Bun.file(path).text();
}

export function embedJSON(path: string): unknown {
  return Bun.file(path).json();
}

// src/index.ts
import { embedFile, embedJSON } from "./macros/embed" with { type: "macro" };

const license = embedFile("./LICENSE");
const config = embedJSON("./config.json");

构建常量

// macros/constants.ts
export function isDev(): boolean {
  return process.env.NODE_ENV !== "production";
}

export function buildDate(): number {
  return Date.now();
}

export function randomId(): string {
  return Math.random().toString(36).slice(2);
}

// src/index.ts
import { isDev, buildDate, randomId } from "./macros/constants" with { type: "macro" };

if (isDev()) {
  console.log("Development mode");
}

const BUILD_ID = randomId();

目录列表

// macros/files.ts
import { readdirSync } from "fs";

export function listRoutes(): string[] {
  return readdirSync("./src/routes")
    .filter(f => f.endsWith(".tsx"))
    .map(f => f.replace(".tsx", ""));
}

// src/router.ts
import { listRoutes } from "./macros/files" with { type: "macro" };

const routes = listRoutes();
// Becomes: const routes = ["home", "about", "users"];

代码生成

// macros/codegen.ts
export function generateTypes(schema: string): string {
  // Parse schema and generate types at build time
  const types = parseSchemaToTypes(schema);
  return types;
}

export function generateAPI(spec: string): string {
  const openapi = JSON.parse(Bun.file(spec).text());
  // Generate API client code
  return generateClientFromOpenAPI(openapi);
}

返回类型

宏可以返回：

// Primitives
export function getString(): string { return "hello"; }
export function getNumber(): number { return 42; }
export function getBoolean(): boolean { return true; }
export function getNull(): null { return null; }

// Objects (serializable)
export function getObject(): object {
  return { key: "value", nested: { a: 1 } };
}

// Arrays
export function getArray(): string[] {
  return ["a", "b", "c"];
}

// Response (for bundler plugins)
export function getResponse(): Response {
  return new Response("content", {
    headers: { "Content-Type": "text/plain" },
  });
}

异步宏

// macros/fetch.ts
export async function fetchSchema(): Promise<object> {
  const response = await fetch("https://api.example.com/schema.json");
  return response.json();
}

// src/index.ts
import { fetchSchema } from "./macros/fetch" with { type: "macro" };

const schema = await fetchSchema();
// Fetched at build time, inlined as object literal

参数

// macros/parameterized.ts
export function repeat(str: string, count: number): string {
  return str.repeat(count);
}

export function formatDate(format: string): string {
  return new Date().toLocaleDateString("en-US", {
    dateStyle: format as any,
  });
}

// src/index.ts
import { repeat, formatDate } from "./macros/parameterized" with { type: "macro" };

const separator = repeat("-", 20);
const date = formatDate("long");

条件代码

// macros/platform.ts
export function platform(): "node" | "bun" | "browser" {
  if (typeof Bun !== "undefined") return "bun";
  if (typeof process !== "undefined") return "node";
  return "browser";
}

// src/index.ts
import { platform } from "./macros/platform" with { type: "macro" };

if (platform() === "bun") {
  // This block is kept or removed at build time
  console.log("Running on Bun");
}

仅在打包时执行

宏只会在打包期间运行：

# Macros executed
bun build src/index.ts --outdir=dist

# Macros NOT executed (runtime)
bun run src/index.ts

错误处理

// macros/safe.ts
export function requireEnv(key: string): string {
  const value = process.env[key];
  if (!value) {
    throw new Error(`Missing required env var: ${key}`);
  }
  return value;
}

// Build fails if env var missing
import { requireEnv } from "./macros/safe" with { type: "macro" };
const secret = requireEnv("API_SECRET");

调试宏

// macros/debug.ts
export function debug(label: string, value: unknown): unknown {
  console.log(`[MACRO] ${label}:`, value);
  return value;
}

// See output during build
bun build src/index.ts --outdir=dist
// [MACRO] config: { ... }

最佳实践

1. 保持宏纯粹 - 避免副作用
2. 返回可序列化的值 - 必须与 JSON 兼容
3. 处理错误 - 在构建失败时抛出有意义的错误
4. 记录依赖项 - 注明所需的文件和环境变量
5. 单独测试 - 宏可以像常规函数一样测试

常见错误

错误	原因	修复方法
Cannot find module	导入路径错误	检查宏文件的位置
Not serializable	返回了函数/类	返回普通数据
Macro failed	宏中发生运行时错误	单独调试宏
Not evaluated	缺少 with { type: "macro" }	添加导入属性

何时加载参考资料

在以下情况加载 references/advanced-patterns.md：

• 复杂的代码生成
• 插件集成
• 构建流水线 检索并展示自定义宏实现模式、与构建系统集成的示例，以及高级打包器插件工作流。

在以下情况加载 references/debugging.md：

• 宏未执行
• 输出不符合预期
• 性能问题 检索调试技巧，提供分步诊断，并针对用户的具体问题给出优化策略。