Build with warning if second entry point not resolved

[djr319]

🙋 feature request

For a project with 2 (or more?) entry files, build with warning if an entry point does not resolve (because of typo or file rename)

🤔 Expected Behavior

With multiple entry points, if one of the files does not resolve, provide a warning "unknown: Entry does not exist".

😯 Current Behavior

Currently, the local dev server will fail, but "Build" will pass without warning.

💁 Possible Solution

Output a warning message at build

Optionally: Fail the build with same message as dev server

🔦 Context

💻 Examples