rollup.defineConfig is undefined at runtime.

[tasshi-me]

• Rollup Version: 2.51.0
• Operating System (or Browser): macOS 11.4
• Node Version (if applicable): 14.17.0
• Link to reproduction (IMPORTANT, read below): https://github.com/tasshi-playground/repro-rollup-defineConfig-undefined

Hi there, and thanks for the great package.
I encountered following unexpected behavior.

Summary

rollup -c failed when rollup.config.js using rollup.defineConfig,
because rollup.defineConfig is not defined at runtime.

FYI: rollup.defineConfig is added in v2.51.0.

• release: https://github.com/rollup/rollup/releases/tag/v2.51.0
• pull request: feat: Export defineConfig defines the auxiliary function of the configuration #4127
• document: 01-command-line-reference.md#config-intellisense

Reproduction

https://github.com/tasshi-playground/repro-rollup-defineConfig-undefined

$ git clone https://github.com/tasshi-playground/repro-rollup-defineConfig-undefined.git
$ cd repro-rollup-defineConfig-undefined
$ npm install
$ npm run build # equal to "rollup -c"

Then, error occur.

Expected Behavior

rollup -c success.

Actual Behavior

rollup -c failed with following error.

[!] TypeError: rollup.defineConfig is not a function
TypeError: rollup.defineConfig is not a function
    at Object.<anonymous> (<project_dir>/rollup.config.js:7:28)
    at Module._compile (internal/modules/cjs/loader.js:1068:30)
    at Object.require.extensions.<computed> [as .js] (<project_dir>/node_modules/rollup/dist/shared/loadConfigFile.js:530:20)
    at Module.load (internal/modules/cjs/loader.js:933:32)
    at Function.Module._load (internal/modules/cjs/loader.js:774:14)
    at Module.require (internal/modules/cjs/loader.js:957:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at loadConfigFromBundledFile (<project_dir>/node_modules/rollup/dist/shared/loadConfigFile.js:538:42)
    at getDefaultFromTranspiledConfigFile (<project_dir>/node_modules/rollup/dist/shared/loadConfigFile.js:522:12)
    at async loadConfigFile (<project_dir>/rollup/dist/shared/loadConfigFile.js:487:15)

with Node.js REPL, rollup module does not contain defineConfig.

Welcome to Node.js v14.17.0.
Type ".help" for more information.
> require("rollup")
{
  VERSION: '2.51.0',
  rollup: [Function: rollup],
  watch: [Function: watch]
}

Cause

rollup.defineConfig is defined in type definition but does not exist at runtime.

• type definition (dist/rollup.d.ts) contains defineConfig
  • this file is copied from src/rollup/types.d.ts in build process

    • shx cp src/rollup/types.d.ts dist/rollup.d.ts

• node entrypoint (src/node-entry.ts) does not export defineConfig