Where in the vue code base is it creating the vue.esm.browser.js file?

问题

I am looking at vue and trying to figure out how they build the vue.esm.browser.js file. Everything else seems to be in ./script/config.js but I can't find anything in there about esm in the browser. Is it using a dependency or something to generate the file?

I also noticed that it isn't listed in the output files when rollup runs.

So my question is, where in the Vue code base is it creating the esm.browser file?

来源：https://stackoverflow.com/questions/53983434/where-in-the-vue-code-base-is-it-creating-the-vue-esm-browser-js-file