Refine Endpoint Module

[vkostyukov]

This PR refines what EndpointModule is and where Endpoint instances are constructed. It doesn't invent anything new but reuses ideas from other libraries solving similar problems.

The following ways of constructing endpoints are now supported.

1. If you prefer being explicit:

import io.finch._, cats.effect.IO
val foo = Endpoint.path[IO, Int] // Endpoint[IO, Int]

2. If you prefer being explicit and also would like type-inference work for you:

import io.finch._, cats.effect.IO
val foo = Endpoint[IO].path[Int] // Endpoint[IO, Int]

3. If you prefer do not repeat yourself and just opt-in for Cats Effect in this source file:

import io.finch._, io.finch.catsEffect._
val foo = path[Int] // Endpoint[IO, Int]

4. If you prefer to have an extension point for your own effect.

object myIO extends Endpoint.Module[MyIO]

import io.finch._, myIO._
val foo = path[Int] // Endpoint[MyIO, Int]

5. If you prefer an extension point for your own effect and want to keep the imports minimal.

import io.finch._

object Foo extends Endpoint.Module[MyIO] {
  val foo = path[Int] // Endpoint[MyIO, Int]
}

What's changed

• All endpoint instances are now defined on Endpoint.* (think Endpoint.param, Endpoint.body) and EndpointModule.* just redirects its calls there similar to how iteratee and Monix do that.
• Module[F[_]] no longer embeds Outputs and ValidationRules are they are not depending on the effect type (io.finch._ imports them as it does today).
• There is no longer tried module implementation, IO is used in tests.
• The syntax package is removed and merged with the rest of the endpoints (note Endpoint.Mappable).
• We're no longer providing the Endpoint type alias from within EndpointModule.
• / is renamed to zero and * is renamed to pathAny (the fewer symbolic APIs we have the better).
• Style has been broken. I want to keep it that way until we replace scalastyle with scalafmt in Code formatter? #196.
• Implicit conversions from Int and Boolean to path-endpoints were removed. Only String is supported now (the less we implicitly convert the better).

[codecov-io]

Codecov Report

Merging #988 into cats-effect will increase coverage by 0.41%.
The diff coverage is 78.41%.

@@               Coverage Diff               @@
##           cats-effect     #988      +/-   ##
===============================================
+ Coverage        84.84%   85.26%   +0.41%     
===============================================
  Files               49       47       -2     
  Lines              884      882       -2     
  Branches            53       50       -3     
===============================================
+ Hits               750      752       +2     
+ Misses             134      130       -4

Impacted Files	Coverage Δ
core/src/main/scala/io/finch/endpoint/method.scala	100% <ø> (ø)
core/src/main/scala/io/finch/internal/Mapper.scala	100% <ø> (ø)
core/src/main/scala/io/finch/package.scala	100% <ø> (ø)	⬆️
...amples/src/main/scala/io/finch/iteratee/Main.scala	0% <0%> (ø)	⬆️
core/src/main/scala/io/finch/endpoint/path.scala	100% <100%> (ø)
core/src/main/scala/io/finch/endpoint/cookie.scala	54.54% <54.54%> (ø)
core/src/main/scala/io/finch/Endpoint.scala	76.31% <75.71%> (-2.26%)	⬇️
...e/src/main/scala/io/finch/endpoint/multipart.scala	75.92% <75.92%> (ø)
core/src/main/scala/io/finch/endpoint/body.scala	79.16% <79.16%> (ø)
core/src/main/scala/io/finch/EndpointModule.scala	85.41% <85.41%> (ø)
... and 9 more

---

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[sergeykolbasov]

What is a benifit of having two almost equivalent method definitions like Endpoint.const[F, _] and EndpointModule[F].const comparing to what it was before with Endpoint[F].const?

[vkostyukov]

What is a benifit of having two almost equivalent method definitions like Endpoint.const and EndpointModule.const comparing to what it was before with Endpoint[F].const?

I feel like this structure promote consistency. Endpoint.* is the only place where instances are defined and it uses the very direct API (a call-site has to supply both F[_] and A). And the EndpointModule enables users to drop the F[_] argument assuming it's always the same thing in their apps.

The very same approach is used in several places where I looked-up. Notably, Monix's Iterant and iteratee libraries are structured in the same.

UPDATE: Endpoint[IO].const("foo") still works today (without any code duplication).

[sergeykolbasov]

LGTM. Few nitpicks of future leftovers

[sergeykolbasov]

evaluate Effect

[sergeykolbasov]

FailedIO here