refactor(pack): ship lightningcss as a core dependency, not an optional peer

lightningcss is already a core dependency (Vite's lightningcss transformer
uses it), so the bundled @tsdown/css can use it directly and CSS bundling
works with no extra install. Revert the optional-peer + loader churn: keep
lightningcss in dependencies (via catalog) and drop the
__vpImportLightningcss helper and the missing-lightningcss snap test.

Author: fengmk2

docs/guide/pack.md

@@ -66,12 +66,4 @@ See the official [tsdown executable docs](https://tsdown.dev/options/exe#executa
 
 ## CSS Bundling
 
-`vp pack` can transform and bundle CSS (including CSS Modules and Lightning CSS optimizations) for your entry points. This support is bundled into Vite+, so you do not need to install `@tsdown/css`.
-
-CSS transforms are powered by [Lightning CSS](https://lightningcss.dev/), which ships as a native module and is an optional peer dependency. Install it when you bundle CSS:
-
-```bash
-vp add -D lightningcss
-```
-
-If it is missing, `vp pack` prints an actionable error telling you to install it.
+`vp pack` can transform and bundle CSS (including CSS Modules and [Lightning CSS](https://lightningcss.dev/) optimizations) for your entry points. This support is bundled into Vite+, so you do not need to install `@tsdown/css` or `lightningcss` separately, it works out of the box.

packages/cli/snap-tests/command-pack-css-missing-lightningcss/block-lightningcss.mjs

@@ -394,8 +394,8 @@ async function bundleTsdown() {
 
   // Everything else in tsdown's peer dependencies stays external. `lightningcss`
   // (a native module) and `postcss` also stay external: `@tsdown/css` pulls them
-  // in, and they cannot be bundled. `lightningcss` becomes an optional peer with
-  // a friendly loader injected by `wireBundledTsdownExtensions()`.
+  // in and they cannot be bundled. Both are core `dependencies`, so they resolve
+  // at runtime and CSS bundling works without users installing anything.
   const tsdownExternal = [
     ...Object.keys(pkgJson.peerDependencies).filter((name) => !bundledTsdownPackages.has(name)),
     'lightningcss',
@@ -585,20 +585,21 @@ async function brandTsdown() {
 
 // Wire the bundled `@tsdown/exe` and `@tsdown/css` extensions into the bundled
 // tsdown so they load from the local chunks instead of resolving external
-// top-level packages, and make `lightningcss` an optional peer with a friendly
-// loader. See https://github.com/voidzero-dev/vite-plus/issues/1586
+// top-level packages. See https://github.com/voidzero-dev/vite-plus/issues/1586
 async function wireBundledTsdownExtensions() {
   const tsdownDistDir = join(projectDir, 'dist/tsdown');
   const buildFiles = await glob(toPosixPath(join(tsdownDistDir, 'build-*.js')), { absolute: true });
   if (buildFiles.length === 0) {
     throw new Error('wireBundledTsdownExtensions: no build chunk found in dist/tsdown/');
   }
 
-  // 1) Route `@tsdown/exe` and `@tsdown/css` to the bundled entries.
-  //    - `importWithError("@tsdown/exe")` dynamically imports a runtime string,
-  //      which rolldown cannot follow, so rewrite the call site to the chunk.
-  //    - `pkgExists("@tsdown/css")` resolves the top-level package at runtime;
-  //      since it is bundled now, force it on and point the import at the chunk.
+  // Route `@tsdown/exe` and `@tsdown/css` to the bundled entries.
+  //   - `importWithError("@tsdown/exe")` dynamically imports a runtime string,
+  //     which rolldown cannot follow, so rewrite the call site to the chunk.
+  //   - `pkgExists("@tsdown/css")` resolves the top-level package at runtime;
+  //     since it is bundled now, force it on and point the import at the chunk.
+  // `@tsdown/css` still imports `lightningcss` (a native module that cannot be
+  // bundled), which resolves to core's own `lightningcss` dependency.
   let exeWired = false;
   let cssWired = false;
   for (const buildFile of buildFiles) {
@@ -628,37 +629,6 @@ async function wireBundledTsdownExtensions() {
   if (!cssWired) {
     throw new Error('wireBundledTsdownExtensions: `pkgExists("@tsdown/css")` not found');
   }
-
-  // 2) `lightningcss` is a native module and an optional peer. Wrap its dynamic
-  //    import so a missing install produces an actionable error instead of a raw
-  //    `Cannot find package 'lightningcss'`.
-  const helper =
-    'async function __vpImportLightningcss() {\n' +
-    '  try {\n' +
-    '    return await import("lightningcss");\n' +
-    '  } catch (cause) {\n' +
-    '    throw new Error(' +
-    '"Cannot find package \\"lightningcss\\". CSS bundling with `vp pack` requires it. ' +
-    'Install it with `vp add -D lightningcss`.", { cause });\n' +
-    '  }\n' +
-    '}\n';
-  const allChunks = await glob(toPosixPath(join(tsdownDistDir, '*.js')), { absolute: true });
-  let lightningcssWired = false;
-  for (const chunk of allChunks) {
-    let content = await readFile(chunk, 'utf-8');
-    if (!content.includes('import("lightningcss")')) {
-      continue;
-    }
-    // Rewrite the call sites first, then prepend the helper (whose own
-    // `import("lightningcss")` must not be rewritten).
-    content = content.replaceAll('import("lightningcss")', '__vpImportLightningcss()');
-    content = helper + content;
-    await writeFile(chunk, content);
-    lightningcssWired = true;
-  }
-  if (!lightningcssWired) {
-    throw new Error('wireBundledTsdownExtensions: `import("lightningcss")` not found');
-  }
 }
 
 // Actually do nothing now, we will polish it in the future when `vitepress` is ready
@@ -755,14 +725,6 @@ async function mergePackageJson() {
   const vitePkg = JSON.parse(await readFile(vitePkgPath, 'utf-8'));
   const destPkg = JSON.parse(await readFile(destPkgPath, 'utf-8'));
 
-  // Track the bundled `@tsdown/css` lightningcss dependency so the optional peer
-  // range stays in lockstep with what the bundled CSS code expects.
-  const require = createRequire(import.meta.url);
-  const tsdownCssPkg = JSON.parse(
-    await readFile(require.resolve('@tsdown/css/package.json'), 'utf-8'),
-  );
-  const lightningcssPeerRange: string = tsdownCssPkg.dependencies?.lightningcss ?? '^1.30.2';
-
   // Merge peerDependencies from tsdown and vite
   destPkg.peerDependencies = {
     ...tsdownPkg.peerDependencies,
@@ -775,17 +737,15 @@ async function mergePackageJson() {
     ...vitePkg.peerDependenciesMeta,
   };
 
-  // `@tsdown/exe` and `@tsdown/css` are bundled into core (see bundleTsdown),
-  // so they must not be advertised as peers anymore. `lightningcss` is a native
-  // module pulled in by the bundled `@tsdown/css` (and Vite's lightningcss
-  // transformer); keep it external as an optional peer so users only install it
-  // when they actually bundle CSS.
+  // `@tsdown/exe` and `@tsdown/css` are bundled into core (see bundleTsdown), so
+  // they must not be advertised as peers anymore. `lightningcss` (which the
+  // bundled `@tsdown/css` and Vite's lightningcss transformer use) stays a core
+  // `dependency`, kept in lockstep with `@tsdown/css` by the upgrade-deps script,
+  // so CSS bundling works without any extra install.
   for (const bundled of ['@tsdown/exe', '@tsdown/css']) {
     delete destPkg.peerDependencies[bundled];
     delete destPkg.peerDependenciesMeta[bundled];
   }
-  destPkg.peerDependencies['lightningcss'] = lightningcssPeerRange;
-  destPkg.peerDependenciesMeta['lightningcss'] = { optional: true };
 
   destPkg.bundledVersions = {
     ...destPkg.bundledVersions,

packages/cli/snap-tests/command-pack-css-missing-lightningcss/package.json

@@ -102,6 +102,7 @@
   "dependencies": {
     "@oxc-project/runtime": "catalog:",
     "@oxc-project/types": "catalog:",
+    "lightningcss": "catalog:",
     "postcss": "^8.5.6"
   },
   "devDependencies": {
@@ -116,7 +117,6 @@
     "@vitejs/devtools": "^0.3.3",
     "es-module-lexer": "^1.7.0",
     "hookable": "^6.0.1",
-    "lightningcss": "^1.32.0",
     "magic-string": "^0.30.21",
     "oxc-parser": "catalog:",
     "oxfmt": "catalog:",
@@ -140,7 +140,6 @@
     "esbuild": "^0.27.0 || ^0.28.0",
     "jiti": ">=1.21.0",
     "less": "^4.0.0",
-    "lightningcss": "^1.32.0",
     "publint": "^0.3.8",
     "sass": "^1.70.0",
     "sass-embedded": "^1.70.0",
@@ -204,9 +203,6 @@
     },
     "yaml": {
       "optional": true
-    },
-    "lightningcss": {
-      "optional": true
     }
   },
   "optionalDependencies": {