606248c662
This commit implements a chunk extension optimization that reduces the number of
output files by merging shared modules into entry chunks when appropriate.
## What's Implemented
### 1. Chunk Extension Optimization
When `preserveEntrySignatures` is set to "allow-extension" (default), shared
modules can be merged into existing entry chunks rather than creating separate
common chunks. This reduces the total number of files that need to be loaded.
Example results:
- With "strict": 2 entry files + 1 common chunk = 3 files
- With "allow-extension": 2 entry files (shared code merged) = 2 files
### 2. preserveEntrySignatures Option
Added a new bundler option with four modes:
- `"strict"`: Prevents chunk extension, maintains exact entry signatures
- `"allow-extension"`: Allows merging shared modules into entries (default)
- `"exports-only"`: Preserves only explicit exports while allowing optimization
- `"false"`: Maximum optimization with no restrictions
### 3. Advanced Chunking API (Structure Only)
Added the API structure for future advanced chunking features:
```javascript
await Bun.build({
entrypoints: ["./app.js"],
splitting: true,
advancedChunks: {
minShareCount: 2,
minSize: 1024,
maxSize: 512000,
groups: [{
name: "vendor",
test: "node_modules",
priority: 10,
type: "javascript"
}]
}
});
```
Note: The advanced chunking configuration is parsed and validated but the
actual chunking logic based on these rules is not yet implemented.
## Technical Details
### Implementation
- Two-phase chunk assignment: collect candidates, then optimize placement
- BitSet-based tracking of which entry points can reach each module
- Module uniqueness enforcement (each module belongs to exactly one chunk)
- Debug-only verification with zero production overhead
### Testing
- 19 tests covering the optimization and edge cases
- Verified backward compatibility
- All tests passing
## Usage
```bash
# CLI
bun build app.js admin.js --splitting --preserve-entry-signatures=allow-extension
# API
await Bun.build({
entrypoints: ["./app.js", "./admin.js"],
splitting: true,
preserveEntrySignatures: "allow-extension"
});
```
This optimization can reduce the number of HTTP requests needed to load a
bundled application by intelligently merging shared code into entry chunks.
Tests
Finding tests
Tests are located in the test/ directory and are organized using the following structure:
test/js/- tests for JavaScript APIs.cli/- tests for commands, configs, and stdout.bundler/- tests for the transpiler/bundler.regression/- tests that reproduce a specific issue.harness.ts- utility functions that can be imported from any test.
The tests in test/js/ directory are further categorized by the type of API.
test/js/bun/- tests forBun-specific APIs.node/- tests for Node.js APIs.web/- tests for Web APIs, likefetch().first_party/- tests for npm packages that are built-in, likeundici.third_party/- tests for npm packages that are not built-in, but are popular, likeesbuild.
Running tests
To run a test, use Bun's built-in test command: bun test.
bun test # Run all tests
bun test js/bun # Only run tests in a directory
bun test sqlite.test.ts # Only run a specific test
If you encounter lots of errors, try running bun install, then trying again.
Writing tests
Tests are written in TypeScript (preferred) or JavaScript using Jest's describe(), test(), and expect() APIs.
import { describe, test, expect } from "bun:test";
import { gcTick } from "harness";
describe("TextEncoder", () => {
test("can encode a string", async () => {
const encoder = new TextEncoder();
const actual = encoder.encode("bun");
await gcTick();
expect(actual).toBe(new Uint8Array([0x62, 0x75, 0x6E]));
});
});
If you are fixing a bug that was reported from a GitHub issue, remember to add a test in the test/regression/ directory.
// test/regression/issue/02005.test.ts
import { it, expect } from "bun:test";
it("regex literal should work with non-latin1", () => {
const text = "这是一段要替换的文字";
expect(text.replace(new RegExp("要替换"), "")).toBe("这是一段的文字");
expect(text.replace(/要替换/, "")).toBe("这是一段的文字");
});
In the future, a bot will automatically close or re-open issues when a regression is detected or resolved.
Zig tests
These tests live in various .zig files throughout Bun's codebase, leveraging Zig's builtin test keyword.
Currently, they're not run automatically nor is there a simple way to run all of them. We will make this better soon.
TypeScript
Test files should be written in TypeScript. The types in packages/bun-types should be updated to support all new APIs. Changes to the .d.ts files in packages/bun-types will be immediately reflected in test files; no build step is necessary.
Writing a test will often require using invalid syntax, e.g. when checking for errors when an invalid input is passed to a function. TypeScript provides a number of escape hatches here.
// @ts-expect-error- This should be your first choice. It tells TypeScript that the next line should fail typechecking.// @ts-ignore- Ignore the next line entirely.// @ts-nocheck- Put this at the top of the file to disable typechecking on the entire file. Useful for autogenerated test files, or when ignoring/disabling type checks an a per-line basis is too onerous.