feat: Add remove-assert plugin for SWC #575

chunghyunleeme · 2026-01-19T07:39:07Z

Summary

Implements a new Wasm plugin for SWC that automatically removes assert() statements during compilation, reducing bundle size and runtime overhead in production builds. This is similar to how Python's -O flag and C's NDEBUG macro eliminate assertions.

Features

✅ Automatic removal of global assert() calls
✅ Removal of imported assert calls (from assert, node:assert, assert/strict, node:assert/strict)
✅ Removes import declarations from assert modules (clean output)
✅ Supports all import styles: default, namespace, and named imports
✅ Handles method calls: assert.ok(), assert.strictEqual(), assert.deepEqual(), etc.
✅ Preserves locally-defined assert functions (scoping aware)
✅ Fully tested with comprehensive test cases
✅ Production build optimization tool

Supported Import Patterns

// All of these import styles are supported and will be removed
import assert from 'assert';
import assert from 'node:assert';
import * as assert from 'assert';
import { assert, fail, ok, strictEqual } from 'assert';
import { strict as assert } from 'assert';

Test Plan

Build plugin in debug mode without warnings
Build plugin in release mode
Run unit tests - all tests passing
Verify snapshot tests match expected output
Test assert removal in function scope
Test assert preservation for local assertions
Test imported assert removal (default, namespace, named imports)
Test assert method calls removal (assert.ok, assert.strictEqual, etc.)
Test import declaration removal

Example Usage

{
  "jsc": {
    "experimental": {
      "plugins": [
        ["@swc/plugin-remove-assert", {}]
      ]
    }
  }
}

Input

import assert from 'node:assert';

export function validateUser(user: User) {
  assert(user.id > 0, 'id must be positive');
  assert.ok(user.name, 'name is required');
  assert.strictEqual(typeof user.email, 'string', 'email must be string');
  return user;
}

Output (production build)

export function validateUser(user) {
  return user;
}

Related Issue

Addresses: https://github.com/swc-project/swc/issues/11449

Implement a new Wasm plugin that removes assert() statements during compilation, reducing bundle size and runtime overhead in production builds. This is similar to how Python's -O flag and C's NDEBUG macro handle assertions. - Supports automatic removal of global assert() calls - Preserves locally-defined assert functions - Fully tested with comprehensive test cases - Works as a production build optimization tool Addresses GitHub issue: swc-project/swc#11449

changeset-bot · 2026-01-19T07:39:11Z

🦋 Changeset detected

Latest commit: 1cc1c43

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@swc/plugin-remove-assert	Minor

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CLAassistant · 2026-01-19T07:39:16Z

All committers have signed the CLA.

kdy1

Can you add some more tests?
The test suite should include test for:

import * as assert from 'assert'
from node:assert
import { assert, fail } from 'assert';
import { assert } from 'assert'; && import { fail } from 'assert'; (in same file)
import { fail } from 'assert'; && import * as assert from 'assert'; (in same file)

Add fixture tests covering various import patterns: - import * as assert from 'assert' - import assert from 'node:assert' - import { assert, fail } from 'assert' - separate import { assert } and import { fail } - mixed import { fail } and import * as assert Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Add WASM-based tests covering various import patterns: - import * as assert from 'assert' - import assert from 'node:assert' - import { assert, fail } from 'assert' - separate import { assert } and import { fail } - mixed import { fail } and import * as assert Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Imported assert identifiers are bound (not unresolved), so assert calls should NOT be removed when assert is imported. Updated the expected output files to reflect the actual behavior. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

The plugin now removes assert calls from modules imported from: - 'assert' - 'node:assert' - 'assert/strict' - 'node:assert/strict' Supports all import styles: - import assert from 'assert' - import * as assert from 'assert' - import { assert, fail, ok } from 'assert' Also handles method calls like assert.ok(), assert.strictEqual(), etc. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

- Update fixture outputs to expect assert calls to be removed - Add test for assert method calls (assert.ok, assert.strictEqual, etc.) - Update vitest snapshots Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

The plugin now removes the entire import declaration when importing from assert modules ('assert', 'node:assert', 'assert/strict', 'node:assert/strict'), not just the assert calls. Before: ```js import assert from 'assert'; ; ``` After: ```js ; ``` Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

kdy1 · 2026-01-21T01:51:31Z

packages/remove-assert/README.tmpl.md

@@ -0,0 +1,22 @@
+# remove-console


Please update this document

…ntation Replace generic remove-console template with remove-assert specific documentation, including proper description, configuration examples, and input/output examples. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

kdy1 · 2026-01-21T03:34:51Z

packages/remove-assert/transform/src/lib.rs

+                    match specifier {
+                        // import assert from 'assert'
+                        ImportSpecifier::Default(default) => {
+                            self.assert_import_ctxts.push(default.local.ctxt);


This is wrong

We should collect default.local.to_id() instead

chunghyunleeme added 2 commits January 19, 2026 16:35

chunghyunleeme added 4 commits January 19, 2026 16:42

chore: Add changeset for remove-assert plugin

ed27965

chore: Update pnpm-lock.yaml

4b56052

fix: Fix test fixture to use remove_assert instead of remove_console

93ba11f

test: Update fixture tests from console to assert

3418630

kdy1 reviewed Jan 19, 2026

View reviewed changes

chunghyunleeme and others added 7 commits January 19, 2026 23:44

chore: Update Cargo.lock for remove-assert plugin

47104a8

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test: Update tests for imported assert removal

a2ea863

- Update fixture outputs to expect assert calls to be removed - Add test for assert method calls (assert.ok, assert.strictEqual, etc.) - Update vitest snapshots Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

chunghyunleeme requested a review from kdy1 January 19, 2026 15:30

kdy1 requested changes Jan 21, 2026

View reviewed changes

packages/remove-assert/README.tmpl.md Outdated

@@ -0,0 +1,22 @@

# remove-console

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kdy1 Jan 21, 2026

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Please update this document

chunghyunleeme requested a review from kdy1 January 21, 2026 03:30

kdy1 reviewed Jan 21, 2026

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Summary

Features

Supported Import Patterns

Test Plan

Example Usage

Input

Output (production build)

Related Issue

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