fix: use deep merge on user-provided rolldown options

Gugustinette · Gugustinette · commit b34bbf056a77 · 2026-06-06T14:42:54.000+02:00
diff --git a/playground/build.mjs b/playground/build.mjs
@@ -7,6 +7,9 @@ async function main() {
     path: "playground/index.ts",
     // temporary file will be kept inside node_modules/.unrun
     debug: true,
+    inputOptions: {
+      plugins: [],
+    },
   });
 }
 
diff --git a/src/utils/bundle.ts b/src/utils/bundle.ts
@@ -13,6 +13,7 @@ import {
   createSourceContextShimsPlugin,
 } from "../plugins";
 import type { ResolvedOptions } from "../options";
+import { deepMerge } from "./deep-merge";
 
 export interface BundleOutput {
   chunk: OutputChunk;
@@ -55,17 +56,18 @@ export async function bundle(options: ResolvedOptions): Promise<BundleOutput> {
     },
     // Hide all logs by default
     logLevel: "silent",
-    // Finally, apply user-provided overrides
-    ...options.inputOptions,
   };
 
+  // Apply user-provided overrides with deep merge
+  const mergedInputOptions = deepMerge(inputOptions, options.inputOptions);
+
   // Apply tsconfig if resolved
   if (tsconfig) {
-    inputOptions.tsconfig = tsconfig;
+    mergedInputOptions.tsconfig = tsconfig;
   }
 
   // Setup bundle
-  const bundle = await rolldown(inputOptions);
+  const bundle = await rolldown(mergedInputOptions);
 
   // Output options (https://rolldown.rs/reference/config-options#outputoptions)
   const outputOptions: OutputOptions = {
@@ -79,12 +81,13 @@ export async function bundle(options: ResolvedOptions): Promise<BundleOutput> {
           },
         }
       : {}),
-    // Apply user-provided overrides last
-    ...options.outputOptions,
   };
 
+  // Apply user-provided overrides with deep merge
+  const mergedOutputOptions = deepMerge(outputOptions, options.outputOptions);
+
   // Generate bundle in memory
-  const rolldownOutput = await bundle.generate(outputOptions);
+  const rolldownOutput = await bundle.generate(mergedOutputOptions);
 
   // Verify that the output is not empty
   if (!rolldownOutput.output[0]) {
diff --git a/src/utils/deep-merge.ts b/src/utils/deep-merge.ts
@@ -0,0 +1,49 @@
+/**
+ * Deeply merges two objects, with the second object taking precedence.
+ * Arrays are concatenated (not replaced).
+ * Undefined values in the source object are ignored (do not override target).
+ * @param target The target object to merge into.
+ * @param source The source object to merge from.
+ * @returns A new object that is the result of deeply merging the source into the target.
+ */
+export function deepMerge<T extends Record<string, any>>(
+  target: T,
+  source: Partial<T> | undefined,
+): T {
+  if (!source) {
+    return target;
+  }
+
+  const result = { ...target };
+
+  for (const key in source) {
+    if (Object.prototype.hasOwnProperty.call(source, key)) {
+      const targetValue = result[key];
+      const sourceValue = source[key];
+
+      if (sourceValue === undefined) {
+        continue;
+      }
+
+      if (Array.isArray(targetValue) && Array.isArray(sourceValue)) {
+        // Concatenate arrays
+        result[key] = [...targetValue, ...sourceValue] as any;
+      } else if (
+        typeof targetValue === "object" &&
+        targetValue !== null &&
+        typeof sourceValue === "object" &&
+        sourceValue !== null &&
+        !Array.isArray(targetValue) &&
+        !Array.isArray(sourceValue)
+      ) {
+        // Recursively merge objects
+        result[key] = deepMerge({ ...targetValue }, sourceValue);
+      } else {
+        // Override with source value
+        result[key] = sourceValue as any;
+      }
+    }
+  }
+
+  return result;
+}

Original file line number	Diff line number	Diff line change
`@@ -7,6 +7,9 @@ async function main() {`
`7`	`7`	`path: "playground/index.ts",`
`8`	`8`	`// temporary file will be kept inside node_modules/.unrun`
`9`	`9`	`debug: true,`
	`10`	`+ inputOptions: {`
	`11`	`+ plugins: [],`
	`12`	`+ },`
`10`	`13`	`});`
`11`	`14`	`}`
`12`	`15`