fix: don't throw when both minimizerOptions and terserOptions are set

Prefer `minimizerOptions` silently when both are provided instead of
throwing. This keeps existing configurations that pass the deprecated
`terserOptions` working unchanged, even if a tooling layer also injects
the new key.

Author: claude

README.md

@@ -413,8 +413,8 @@ reused for every minimizer.
 > **Note**
 >
 > `terserOptions` is kept as a deprecated alias of `minimizerOptions` for
-> backwards compatibility — passing either is equivalent. Passing both at the
-> same time throws an error. Prefer `minimizerOptions` in new code.
+> backwards compatibility — passing either is equivalent. If both are set,
+> `minimizerOptions` wins. Prefer `minimizerOptions` in new code.
 
 **webpack.config.js**
 

src/index.js

@@ -192,18 +192,15 @@ class TerserPlugin {
       exclude,
     } = options || {};
 
-    if (
-      typeof minimizerOptions !== "undefined" &&
-      typeof terserOptions !== "undefined"
-    ) {
-      throw new Error(
-        "The `minimizerOptions` and `terserOptions` options can't be used together. Please use only `minimizerOptions` (`terserOptions` is a deprecated alias).",
-      );
-    }
-
+    // `terserOptions` is a deprecated alias of `minimizerOptions`; prefer the
+    // new name when both are provided.
     const resolvedMinimizerOptions =
       /** @type {MinimizerOptions<T>} */
-      (minimizerOptions || terserOptions || {});
+      (
+        typeof minimizerOptions !== "undefined"
+          ? minimizerOptions
+          : terserOptions || {}
+      );
 
     /**
      * @private

test/__snapshots__/validate-options.test.js.snap

@@ -233,5 +233,3 @@ exports[`validation validate 19`] = `
     * options.minimizerOptions should be an array:
       [object { … }, ...] (should not have fewer than 1 item)"
 `;
-
-exports[`validation validate 20`] = `"The \`minimizerOptions\` and \`terserOptions\` options can't be used together. Please use only \`minimizerOptions\` (\`terserOptions\` is a deprecated alias)."`;

test/minimizerOptions-option.test.js

@@ -46,14 +46,13 @@ describe("minimizerOptions option", () => {
     );
   });
 
-  it("should throw when both `minimizerOptions` and `terserOptions` are provided", () => {
-    expect(
-      () =>
-        new TerserPlugin({
-          minimizerOptions: { mangle: false },
-          terserOptions: { mangle: false },
-        }),
-    ).toThrow(/can't be used together/);
+  it("should prefer `minimizerOptions` when both `minimizerOptions` and `terserOptions` are provided", () => {
+    const plugin = new TerserPlugin({
+      minimizerOptions: { mangle: false },
+      terserOptions: { mangle: true, compress: false },
+    });
+
+    expect(plugin.options.minimizer.options).toEqual({ mangle: false });
   });
 
   it("should default to an empty object when neither option is provided", () => {

test/validate-options.test.js

@@ -333,7 +333,7 @@ describe("validation", () => {
         minimizerOptions: { ecma: 5 },
         terserOptions: { ecma: 5 },
       });
-    }).toThrowErrorMatchingSnapshot();
+    }).not.toThrow();
   });
 });
 /* eslint-enable no-new */