astutil.DeleteNamedImport is documented as:

// DeleteNamedImport deletes the import with the given name and path from the file f, if present.

And it works as expected. It's a low-level AST manipulation primitive that allows one to delete the exact import statement with the provided name and import path.

astutil.AddNamedImport has a symmetrical signature, and its documentation suggests it would do the symmetrical operation of adding an optionally renamed import.

However, it has a bug where once the AST has an import with the specified import path, it's not possible to add other imports with the same import path but different names.

I have a fix with test cases, will send a CL soon. /cc @heschik @alandonovan

This bug is causing #16411.