From 22051828d94057b98518e6761505d08d70b2c525 Mon Sep 17 00:00:00 2001
From: Alec Larson <1925840+aleclarson@users.noreply.github.com>
Date: Mon, 11 Oct 2021 20:13:54 -0400
Subject: [PATCH] fix: respect "sideEffects: true" in package.json

We can assume a package has side effects in this case. This is basically a way
to force Rollup to always include the package when imported.
---
 packages/vite/src/node/packages.ts | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/packages/vite/src/node/packages.ts b/packages/vite/src/node/packages.ts
index 8b769020a05853..80f226261eccea 100644
--- a/packages/vite/src/node/packages.ts
+++ b/packages/vite/src/node/packages.ts
@@ -94,13 +94,19 @@ export function loadPackageData(
 
   const data = JSON.parse(fs.readFileSync(pkgPath, 'utf-8'))
   const pkgDir = path.dirname(pkgPath)
+
+  // When the "sideEffects" field is defined, we can assume modules
+  // in the package are either side effect-free or not, which means
+  // Rollup doesn't have to statically analyze the AST.
   const { sideEffects } = data
-  let hasSideEffects: (id: string) => boolean
+  let hasSideEffects: (id: string) => boolean | 'no-treeshake'
   if (typeof sideEffects === 'boolean') {
-    hasSideEffects = () => sideEffects
+    hasSideEffects = () => sideEffects && 'no-treeshake'
   } else if (Array.isArray(sideEffects)) {
-    hasSideEffects = createFilter(sideEffects, null, { resolve: pkgDir })
+    const filter = createFilter(sideEffects, null, { resolve: pkgDir })
+    hasSideEffects = (id) => filter(id) && 'no-treeshake'
   } else {
+    // Statically analyze each module for side effects.
     hasSideEffects = () => true
   }