fix: merge environments.*.resolve.noExternal properly (vitejs#20077)

Author: sapphi-red

packages/vite/src/node/__tests__/config.spec.ts

@@ -189,6 +189,42 @@ describe('mergeConfig', () => {
     expect(mergeConfig(newConfig, baseConfig)).toEqual(mergedConfig)
   })
 
+  test('handles environments.*.resolve.noExternal', () => {
+    const baseConfig = {
+      environments: {
+        ssr: {
+          resolve: {
+            noExternal: true,
+          },
+        },
+      },
+    }
+
+    const newConfig = {
+      environments: {
+        ssr: {
+          resolve: {
+            noExternal: ['foo'],
+          },
+        },
+      },
+    }
+
+    const mergedConfig = {
+      environments: {
+        ssr: {
+          resolve: {
+            noExternal: true,
+          },
+        },
+      },
+    }
+
+    // merging either ways, `resolve.noExternal: true` should take highest priority
+    expect(mergeConfig(baseConfig, newConfig)).toEqual(mergedConfig)
+    expect(mergeConfig(newConfig, baseConfig)).toEqual(mergedConfig)
+  })
+
   test('handles server.hmr.server', () => {
     const httpServer = http.createServer()
 

packages/vite/src/node/utils.ts

@@ -1211,6 +1211,8 @@ function mergeWithDefaultsRecursively<
   return merged as MergeWithDefaultsResult<D, V>
 }
 
+const environmentPathRE = /^environments\.[^.]+$/
+
 export function mergeWithDefaults<
   D extends Record<string, any>,
   V extends Record<string, any>,
@@ -1272,7 +1274,10 @@ function mergeConfigRecursively(
       merged[key] = mergeConfigRecursively(
         existing,
         value,
-        rootPath ? `${rootPath}.${key}` : key,
+        // treat environment.* as root
+        rootPath && !environmentPathRE.test(rootPath)
+          ? `${rootPath}.${key}`
+          : key,
       )
       continue
     }