Warn if context values passed to createPage are different types than others or empty

[KyleAMathews]

Someone creating pages could run into a mysterious GraphQL error if any of the pages context has missing information:

Errors:
GraphQLError: Variable "$slug" of required type "String!" was not provided.

This is hard for someone new to Gatsby to debug. We should check against this and warn.

[mainframev]

yeah, right now have this issue, trying to fix, but without result :(

[BerlinaLI]

i encounter this issue and found out it is because i didnot write slug in graphql query in the create page function in my gatsby node file

[Jonqth]

Hi @KyleAMathews wanted to know if there's any update on this.

I'm using a starter for dato, my request in gatsby-node.js work just fine with gatsby develop although the error is till log when building.

When i try gatsby build the same exact error you mentioned pops up, as if there's no context provided to my request.

EDIT: So, not so long after posting this i found that the problem came from overriding what createPage() does in gatsby-node.js by having my components inside /pages when for the contextto be actually passed onto the template the component needs to be inside /templates

[peterjaap]

@Jonqth thanks so much for that last edit. Finally fixed this issue after hours of hunting..!

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[alanshortis]

I have run into this error today - when creating pages from a folder of .mdx files, I was defining a component in createPage that lives in my src/pages folder. Moving my post component to src/components avoids it.

Any reason this should be the case? It's not a big deal, but I'd prefer to have the component in my pages folder since it's creating pages.

All pages are created as expected, I just get this error.

[tianzhich]

I have run into this error when migrating from v1 to v2, the context values passed to createPage are same types and not null.

Anyone have same problems?

[whalesingswee]

@tianzhich I was able to fix the problem after moving my post to /src/components instead of using it inside /src/pages as @alanshortis mentioned. Thanks!

[tianzhich]

I solved in #15977 cause the difference between StaticQuery and page query.

Maybe it could help someone.