Fix unnecessary nesting of infix queries

[mosyp]

Fixes #1058

Problem

InfixContext of SqlQuery always produces a nested query, sometimes this is unnecessary, see issue example.

Solution

Unnest queries.

implicit class ForUpdate[T](q: Query[T]) {
  def forUpdate = quote(infix"$q FOR UPDATE".as[Query[T]])
}
run(query[Person].forUpdate)

// before
// SELECT p.id, p.name, p.age FROM (SELECT * FROM Person p WHERE p.age < 18 FOR UPDATE) p	

// after
// SELECT p.name, p.age FROM person p WHERE p.age < 18 FOR UPDATE

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

@getquill/maintainers

[jilen]

I am afraid this will break user defined infix.map(a => f(a)) call

[mosyp]

@jilen Thanks for a review! Could you post an example? There's a test which handles that 6a94603#diff-e564af4387151d9877a17343b828b795R1050. ExpandMappedInfix is applied before the latest Normalize so user defined map will be normalized with expanded map in ExpandMappedInfix. However if there's any known case please share and I will include them in test

[jilen]

@mentegy For example, postgresql's Factorial (or any other postfix operator)

infix("$i !").map(x => f(x))       

Will this transformation break such operator ?

[mosyp]

@jilen well that won't be possible since map is not available for Quoted[T], e.g:

    implicit class PostfixOps[T](v: T) {
      def fact = quote(infix"$v!".as[T])
    }
 run {
      q.map(e => e.id.fact) // no map available after fact
    }

So no known for me places where it could be broken. But I've added additional restriction, see updated pattern matching below, hence transformation will be applied only if q is a query in infix"$q ..."

[mosyp]

These changes completely has broken spark module, @deusaquilus any ideas why?

[mosyp]

Now, transformation is applied only if q is a query in infix"$q ..."

[mosyp]

wow seems like these changes fixed quill-spark errors, thank you @jilen !

[fwbrasil]

The solution introduces special handling for when the infix starts with a query, which might be confusing to users and break existing queries. I think it's a reasonable tradeoff, though. Could you update the readme and the changelog accordingly? Thank you!