Fix join subquery+map+distinct and sortBy+distinct

[deusaquilus]

Fixes #1446, #1447 and #1472 as well as #1463.

@fwbrasil I would appreciate it if you could review AST transformation changes. This one seems to be a very simple solution. Am I missing anything?
Alternatively, maybe every single case of DetachableMap in ApplyMap should have a variant with Distinct(DetachableMap(...))?

Problem

Join+Distinct+Map fails:

case class Person(id: Int, name: String, age: Int)
case class Membership(personId: Int, team: Int)

val m = run(
  query[Person]
    .join(
      query[Membership]
        .filter(liftQuery(Set(1,2,3)) contains _.team)
        .map(_.personId)
        .distinct
    )
    .on(_.id == _)
    .map(_._1)
)

Results in:

exception during macro expansion: 
java.lang.IllegalStateException: The monad composition can't be expressed using applicative joins.

Solution

To fix #1446 add the following clause to ApplyMap:

      // a.*join(b.map(c => d).distinct).on((iA, iB) => on)
      //    a.*join(b.distinct).on((iA, c) => on[iB := d]).map(t => (t._1, d[c := t._2]))
      case Join(tpe, a, Distinct(DetachableMap(b, c, d)), iA, iB, on) =>
        val onr = BetaReduction(on, iB -> d)
        val t = Ident("t")
        val t1 = Property(t, "_1")
        val t2 = BetaReduction(d, c -> Property(t, "_2"))
        Some(Map(Join(tpe, a, Distinct(b), iA, c, onr), t, Tuple(List(t1, t2))))

The following is then returned:

SELECT x1.id, x1.name, x1.age, m.person_id FROM person x1 INNER JOIN (SELECT DISTINCT x.person_id FROM membership x) AS m ON x1.id = m.person_id

Same thing with #1447, add the following to ApplyMap:

      // a.map(b => c).sortBy(d => e).distinct =>
      //    a.sortBy(b => e[d := c]).map(b => c).distinct
      case SortBy(Distinct(DetachableMap(a, b, c)), d, e, f) =>
        val er = BetaReduction(e, d -> c)
        Some(Distinct(Map(SortBy(a, b, er, f), b, c)))

Then you will get:

SELECT x5._1id, x5._1name, x5._1age, x5._2person_id, x5._2team FROM (SELECT DISTINCT x3.age AS _1age, x3.id AS _1id, x3.name AS _1name, x4.team AS _2team, x4.person_id AS _2person_id FROM person x3 INNER JOIN membership x4 ON x3.id = x4.person_id ORDER BY x3.id DESC) AS x5

• 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

[fwbrasil]

This transformation doesn't seem valid. In b.map(c => d).distinct, it'll return distinct mapped values, in b.distinct it'll return distinct records considering all columns

[deusaquilus]

Good point. I took this out.

[deusaquilus]

The merged implementation also fixed #1463.