Support rewriting specifiers in dynamic imports for `transform` entry mode

Describe the feature

Hi!

I was trying the transform entry type and noticed that import specifier rewriting works for static imports, but not for dynamic imports.

Example setup:

src/hello-world.ts

export default () => {
  return "hello-world";
};

src/index.ts

const { default: helloWorld } = await import("./hello-world.ts");
console.log(helloWorld());

build.config.ts

import { defineBuildConfig } from "obuild/config";

export default defineBuildConfig({
  entries: [
    {
      type: "transform",
      input: "./src",
      outDir: "./dist",
      dts: false
    }
  ]
});

The generated output in dist/index.mjs dynamic import remains:

await import("./hello-world.ts");

instead of:

await import("./hello-world.mjs");

Even though dist/hello-world.mjs file was generated.

I was wondering if dynamic imports are intentionally excluded, if they are I may be completely wrong here.

Would you be open to adding support for rewriting dynamic import specifiers as well? For example, adding a TransformEntry option like:

rewriteDynamicImportExtensions: true

(or another name that better fits) could enable transforming .ts extensions from dynamic imports

Solution

I tried implementing this change in a fork, it worked for me but I'm not an expert in build tools so I'm not sure if this'd be the right approach as it only rewrites string literals

https://github.com/unjs/obuild/blob/776eab2ae2ed6aa16e83829cc6d5831d8fd3a68a/src/builders/transform.ts#L202-L214

Thanks!

Additional information

• Would you be willing to help implement this feature?

Start in src/builders/transform.ts around the linked lines and compare how static import specifiers are rewritten with the dynamic-import case. Use the provided src/index.ts, src/hello-world.ts, and build.config.ts example to check the generated dist/index.mjs. Done means the dynamic import points to the generated .mjs file while preserving existing transform behavior.