codegen: improve "could not find field" error message

[fnune]

#97

I've considered adding newlines in between but I don't know if there's any existing convention that would conflict with that.

[fnune]

query RepoView($owner: String!, $name: String!) {
  bananas
  repository(owner: $owner, name: $name) {

// Etc

error: proc-macro derive panicked
  --> src/main.rs:23:10
   |
23 | #[derive(GraphQLQuery)]
   |          ^^^^^^^^^^^^
   |
   = help: message: Code generation failed.
           Could not find field `bananas`. Available fields: `__typename, codeOfConduct, codesOfConduct, license, licenses, marketplaceCategories, marketplaceCategory, marketplaceListing, marketplaceListings, meta, node, nodes, organization, rateLimit, relay, repository, repositoryOwner, resource, search, topic, user, viewer`.    

[mathstuf]

I think Itertools::format would just be better.

fields.iter().map(|ref field| &field.name).format("`, `")

This keeps the field names enclosed in "`", but leaves the commas without markup.

[fnune]

That does look better. Added as an additional commit so it can be reviewed separately.

[mathstuf]

This as_str seems superfluous now (same below).

[fnune]

Right - thanks!

[tomhoule]

Looks good! We discussed the iter formatting issue on another channel - we should address that concern, rebase and then let's merge this.

[fnune]

So I should rebase and then do the thing without itertools?

[tomhoule]

yep - for the itertools part, you can implement a Display helper, something like:

struct CommaSeparated<T>(T);

impl<A, B> std::fmt::Display for CommaSeparated<A>
where A: Iter<Item=B>,
  B: Display {
 ....
}

[tomhoule]

If it's too hard we can think about keeping the itertools dependency.

[tomhoule]

@fnune the codebase has changed quite a bit since this PR was opened :)

[mathstuf]

Is this something we should revisit? Improving error messages is almost always a good thing IMO.

[tomhoule]

Is this something we should revisit? Improving error messages is almost always a good thing IMO.

yeah definitely. We could have an issue so we don't forget