Allow page queries and fragments to be shadowed by themes.

[laurenskling]

I'm heavily invested into themes. It helps me split code that I share between websites I build. If I create a new site that uses feature X and Y, just install the themes.

Now say, those themes are extending GraphQL data on my core schema. I can achieve this with the createTypes and createResolvers functions. But adding these new fields into my GraphQL query are a different story..

If I shadow a file that contains a pageQuery or a fragment, both will be included into the Gatsby ecosystem. Resulting in lots of warnings (#23729). Bypassing the pageQuery errors is possible, just give them seperate names. Fragments however, need to have a fixed name and the need to exist. So shadowing them is not possible (since the fragment name will be scraped twice and that will error/bug). And only including when needed is not possible, since the fragment needs to exist in both cases; with or without the theme.

If allowing me to shadow files with fragments in them, and this is handled correctly, I can shape my code so beautifully dynamic and pluggable. I could create a fallback fragment loading nothing much, and a shadow fragment that actually does the work. This would be my dream.