[Anber]

Summary

The tsup README says it is no longer actively maintained and recommends tsdown. @linaria/atomic, @linaria/core and @linaria/react now build dist/ with tsdown 0.23.1; the published files keep their paths, export names and module specifiers.

 // packages/core/package.json
-"build:dist": "tsup --format cjs,esm",
+"build:dist": "tsdown --format cjs,esm",
-"tsup": { "entry": ["src/index.ts", "src/processors/css.ts"], "splitting": false, "sourcemap": true, "clean": true }
+"tsdown": [  // one config per entry: 3 in atomic, 2 in core, 2 in react
+  { "entry": ["src/index.ts"], "root": "src", "sourcemap": true, "clean": true,
+    "cjsDefault": false, "dts": false, "fixedExtension": false,
+    "outputOptions": { "esModule": true, "strict": true } },
+  { "entry": ["src/processors/css.ts"], /* same options */ }
+]

 // package.json (and the `sortFirst` key in .syncpackrc.js)
-"tsup": "^7.2.0",
+"tsdown": "0.23.1",

Why each option (the tsdown defaults differ from the tsup config):

• One config per entry, root: "src": tsdown has no splitting: false. One config for all entries emitted shared chunks (atomize-* in atomic, rolldown-runtime-* in react), which added published files and changed a testkit snapshot. root keeps dist/processors/*.
• fixedExtension: false: without a "type" field tsdown writes .cjs, but main, exports and the hand-written processors/*.js use .js and .mjs.
• cjsDefault: false: processors only have a default export, which tsdown would turn into module.exports = ...; the wrappers read .default.
• dts: false: tsdown enables declarations when a manifest has types; tsc already writes types/.
• sourcemap: true, clean: true: as before; source maps are off by default.
• outputOptions.esModule and strict: rolldown sets __esModule only for entries with a default export and "use strict" only if the source has it; tsup always did both.
• Exact pin: with ^0.23.1 a regenerated lockfile would take 0.23.2 (2026-10-23, under a week old).

Lockfile

• 27 package keys added (tsdown 0.23.1 and its dependencies), 51 removed (tsup 7.2.0 and its dependencies). No package that stays changes version; rolldown stays 1.2.14 (1.2.15 is from 2026-10-21).
• Registry dates, checked 2026-10-25: tsdown 0.23.1 on 2026-10-10; rolldown-plugin-dts 0.28.8, cac 7.1.0 and the 17 yuku packages on 2026-10-11; the other seven are older (the newest on 2026-09-18). All 27 are at least 13 days old.
• Seven versions already locked and under a week old (astro 7.4.1, vite 8.3.5, devframe, @devframes/hub and @devframes/json-render 1.2.6, @wyw-in-js/vite and @wyw-in-js/webpack-loader 2.7.0) only get a new peer suffix in their snapshot keys.

Evidence

• Published files from npm pack --dry-run --json in the nine published packages, after a clean forced build with tsup 7.2.0 and with tsdown: 149 files, same paths. Two clean builds of each side hash identically. The six packages that are not bundled are byte-identical.
• 31 paths differ in content (28 dist files, 3 package.json; the manifests only in build:dist and the config key). In dist: rolldown's formatting and regenerated source maps with fewer sources; CommonJS exports are plain data properties instead of getters, with a Symbol.toStringTag of Module; comments such as the JSDoc of cx are kept; another interop helper.
• Surface unchanged: export names, __esModule and typeof default of every entry and wrapper, and the module specifiers of all 14 dist files are identical; the 7 CommonJS files still start with "use strict"; all 14 parse as ES2022. dist/processors/styled.mjs of atomic and react cannot be imported natively in Node, before and after (resolve has no named export sync).
• Forced build 16 tasks; core 4 tests; react 22 tests, 17 snapshots; testkit 150 passed, 2 skipped, 279 snapshots, none changed; pnpm check:all 32 tasks plus eslint and syncpack. build:dist --watch in core rebuilds dist/index.js after an edit and after the revert, keeping dist/processors/*.

# Node 24.22.0, pnpm 9.15.9
pnpm install --frozen-lockfile --ignore-scripts
pnpm install --frozen-lockfile --ignore-scripts --strict-peer-dependencies
pnpm clean && pnpm exec turbo run build --force
pnpm --filter ./packages/core test
pnpm --filter ./packages/react test
pnpm --filter ./packages/testkit test
pnpm check:all

Node floor

tsdown 0.23.1 needs Node ^22.18.0 || ^24.11.0 || >=26.0.0, narrower than engines.node >=22.12.0, which stays. The CI matrix (22.x, 24.x) is inside it; Node 22.12 to 22.17 only gets an install warning. The output language level now follows engines.node instead of the es2022 tsconfig target.

Changeset

.changeset/build-with-tsdown.md, patch for the three packages:

Switch the build of the published dist files to tsdown; the file list, the export names and the module specifiers of every entry stay the same.

Left out

• Raising engines.node; pinning the output target.
• A shared config module for the repeated options.
• The six babel and tsc packages; declarations stay with tsc.

Not verified

• A CI run of this pull request.
• A build on Node 22.12 to 22.17 (all runs used 24.22.0).
• The first commit alone: it still has the shared chunks; the pull request is meant to be squashed.
• A merge with other changes to pnpm-lock.yaml, which would need the lockfile regenerated.

[changeset-bot]

🦋 Changeset detected

Latest commit: a296be1

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

This PR includes changesets to release 9 packages

Name	Type
@linaria/atomic	Patch
@linaria/core	Patch
@linaria/react	Patch
@linaria/babel-plugin-interop	Patch
linaria	Patch
@linaria/postcss-linaria	Patch
@linaria/server	Patch
@linaria/stylelint-config-standard-linaria	Patch
@linaria/stylelint	Patch

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