From 5e037ae0a2b3095d202a32abaac3fe2e5920bc44 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Mon, 13 Nov 2023 14:54:01 -0500
Subject: [PATCH] enforce treeshakeability

---
 packages/svelte/package.json                  |  3 +-
 .../svelte/scripts/check-treeshakeability.js  | 38 +++++++++++++++++++
 pnpm-lock.yaml                                | 15 ++++++++
 3 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 packages/svelte/scripts/check-treeshakeability.js

diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index 91f313a2a4..b689111dbb 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -90,7 +90,7 @@
     "templating"
   ],
   "scripts": {
-    "build": "rollup -c && node scripts/build.js",
+    "build": "rollup -c && node scripts/build.js && node scripts/check-treeshakeability.js",
     "watch": "rollup -cw",
     "check": "tsc && cd ./tests/types && tsc",
     "check:watch": "tsc --watch",
@@ -103,6 +103,7 @@
     "@rollup/plugin-commonjs": "^25.0.7",
     "@rollup/plugin-node-resolve": "^15.2.3",
     "@rollup/plugin-terser": "^0.4.4",
+    "@rollup/plugin-virtual": "^3.0.2",
     "@types/aria-query": "^5.0.3",
     "@types/estree": "^1.0.5",
     "dts-buddy": "^0.4.0",
diff --git a/packages/svelte/scripts/check-treeshakeability.js b/packages/svelte/scripts/check-treeshakeability.js
new file mode 100644
index 0000000000..bdcdcc9ef6
--- /dev/null
+++ b/packages/svelte/scripts/check-treeshakeability.js
@@ -0,0 +1,38 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { rollup } from 'rollup';
+import virtual from '@rollup/plugin-virtual';
+
+const pkg = JSON.parse(fs.readFileSync('package.json', 'utf8'));
+
+for (const key in pkg.exports) {
+	for (const type of ['browser', 'default']) {
+		if (!pkg.exports[key][type]) continue;
+
+		const resolved = path.resolve(pkg.exports[key][type]);
+
+		const bundle = await rollup({
+			input: '__entry__',
+			plugins: [
+				virtual({
+					__entry__: `import ${JSON.stringify(resolved)}`
+				})
+			],
+			onwarn: (warning, handle) => {
+				// if (warning.code !== 'EMPTY_BUNDLE') handle(warning);
+			}
+		});
+
+		const { output } = await bundle.generate({});
+
+		if (output.length > 1) {
+			throw new Error('errr what');
+		}
+
+		const { code } = output[0];
+		if (code.trim()) {
+			console.error(code);
+			throw new Error(`${path.join(pkg.name, key)} ${type} export is not tree-shakeable`);
+		}
+	}
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index cb0e47baa7..1dffc51f17 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -108,6 +108,9 @@ importers:
       '@rollup/plugin-terser':
         specifier: ^0.4.4
         version: 0.4.4(rollup@4.3.0)
+      '@rollup/plugin-virtual':
+        specifier: ^3.0.2
+        version: 3.0.2(rollup@4.3.0)
       '@types/aria-query':
         specifier: ^5.0.3
         version: 5.0.4
@@ -1962,6 +1965,18 @@ packages:
       terser: 5.24.0
     dev: true
 
+  /@rollup/plugin-virtual@3.0.2(rollup@4.3.0):
+    resolution: {integrity: sha512-10monEYsBp3scM4/ND4LNH5Rxvh3e/cVeL3jWTgZ2SrQ+BmUoQcopVQvnaMcOnykb1VkxUFuDAN+0FnpTFRy2A==}
+    engines: {node: '>=14.0.0'}
+    peerDependencies:
+      rollup: ^1.20.0||^2.0.0||^3.0.0||^4.0.0
+    peerDependenciesMeta:
+      rollup:
+        optional: true
+    dependencies:
+      rollup: 4.3.0
+    dev: true
+
   /@rollup/pluginutils@4.2.1:
     resolution: {integrity: sha512-iKnFXr7NkdZAIHiIWE+BX5ULi/ucVFYWD6TbAV+rZctiRTY2PL6tsIKhoIOaoskiWAkgu+VsbXgUVDNLHf+InQ==}
     engines: {node: '>= 8.0.0'}