How to build package that depends on ethers with rollup?

[PaulRBerg]

Description

I am using the following ethers packages in my project:

• @ethersproject/abi
• @ethersproject/address
• @ethersproject/keccak256

My goal is to build the package for two JS environments: Node.Js and the web browser. I have opted in to use Rollup for that:

"build": "yarn build:node && yarn build:browser",
"build:browser": "yarn rollup",
"build:node": "tsc --project ./tsconfig.prod.json",

Here's a link to my Rollup configuration file. The question is: why I am getting this warning and how can I get rid of it?

(!) You have passed an unrecognized option
Unknown output options: mainFields. Allowed options: amd, assetFileNames, banner, chunkFileNames, compact, dir, dynamicImportFunction, entryFileNames, esModule, exports, extend, externalLiveBindings, file, footer, format, freeze, generatedCode, globals, hoistTransitiveImports, indent, inlineDynamicImports, interop, intro, manualChunks, minifyInternalExports, name, namespaceToStringTag, noConflict, outro, paths, plugins, preferConst, preserveModules, preserveModulesRoot, sanitizeFileName, sourcemap, sourcemapExcludeSources, sourcemapFile, sourcemapPathTransform, strict, systemNullSetters, validate

Environment:

• @ethersproject/ab@5.4.1
• @ethersproject/address@5.4.0
• @ethersproject/keccak256@5.4.0
• rollup@2.58.0
• typescript@4.4.3