From a76919c5cd19278ee397e9438ec89b68d336a711 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/plugins/resolve.ts | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/packages/vite/src/node/plugins/resolve.ts b/packages/vite/src/node/plugins/resolve.ts
index 9b8519a43119c0..f58e0219fadf82 100644
--- a/packages/vite/src/node/plugins/resolve.ts
+++ b/packages/vite/src/node/plugins/resolve.ts
@@ -583,7 +583,7 @@ export function tryOptimizedResolve(
 
 export interface PackageData {
   dir: string
-  hasSideEffects: (id: string) => boolean
+  hasSideEffects: (id: string) => boolean | 'no-treeshake'
   webResolvedImports: Record<string, string | undefined>
   nodeResolvedImports: Record<string, string | undefined>
   setResolvedCache: (key: string, entry: string, targetWeb: boolean) => void
@@ -621,13 +621,19 @@ export function resolvePackageData(
 function loadPackageData(pkgPath: string, cacheKey = pkgPath) {
   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
   }