Hi @Auspicus, thanks for opening up this PR. Before we approve and merge this, could you explain a little more what is in this app-* entry point? Any chance that we might miss source maps if we ignore it (i.e. don't upload source maps)?

@Lms24 The current codebase actually ignores the app-* entrypoint. I think previous versions of Gatsby (before v4) would only bundle core code in the app-* entrypoint but somewhere in v4 this changed. This has at least been what I have found from the few sites I've looked at. The change here removes app-* from the ignore list so its sourcemaps are included and uploaded to Sentry. I am following up with the Gatsby team to confirm this and will respond here once I know more.

Right, I mixed this up. Thanks, for following up. Just ping any of us when you have an answer, then we'll give this PR another review. Cheers!

@Lms24 Here's a start I guess. I'm still trying to dig through the Webpack config to point to the exact places where this is happening but the docs explain that if a module is included in more than one chunk it may end up in commons-* or app-* implying that user code may end up in app-*.

EDIT: Here's the relevant Webpack config although it's hard to pinpoint a specific line that would dictate that app-* may contain user code.

EDIT2: There's also this blog post from Ben Robertson about the contents of the different chunks: https://ben.robertson.is/notes/gatsby-and-bundle-chunking

EDIT3: And Gatsby docs for more detailed explanation: https://www.gatsbyjs.com/docs/how-code-splitting-works/