ExecuteQuery refactoring

[lucianjon]

Background

There are problems with ExecutableSchema.ExecuteQuery which have been hiding bugs. It's quite a long function that does many things and the fact it's a receiver function on ExecutableSchema means it has access to a lot of mutable state it probably shouldn't. Eventually I'd like to entirely redo this function as I don't like the mutex and using shared state approach. I'd rather each instance of a query execution have access to their own copy of the variables. I think extracting out the core execution pipeline from ExecutableSchema will make bramble more modular too.

Bugs Fixed

One of the first things the function does is filter down the schema based on the permissions in the request context. Unfortunately there were plenty of cases further down that just accessed the schema from ExecutableSchema.MergedSchema rather than using the filtered schema, essentially bypassing the authorization.

Changes

• There were a couple instances of redundant checks, like calling graphql.GetOperationContext(ctx) as that will actually panic.
• The extensions were registered right at the end of the function and so if there were any errors you'd never get useful debugging info, that is now at the top.
• Remove errors from formatResponseData and unionAndTrimSelectionSet. There was only one legitimate error in formatResponseData and that was from calling json.Marshal. Given this data is already guaranteed to be JSON I decided to panic instead.
• Remove a bunch of functions from ExecutableSchema that have no business being on it. There was another bug hiding in resolveSchema due to this.

[codecov-commenter]

Codecov Report

Merging #141 (e801f28) into main (9950bc0) will increase coverage by 0.78%. The diff coverage is 82.45%.

@@            Coverage Diff             @@
##             main     #141      +/-   ##
==========================================
+ Coverage   69.61%   70.40%   +0.78%     
==========================================
  Files          24       24              
  Lines        2630     2602      -28     
==========================================
+ Hits         1831     1832       +1     
+ Misses        668      650      -18     
+ Partials      131      120      -11     

Impacted Files	Coverage Δ
execution.go	78.63% <79.54%> (+1.75%)	:arrow_up:
query_execution.go	77.00% <92.30%> (+3.07%)	:arrow_up:

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