Add documentation for the directory layout and MultiScala

Author: MasseGuillaume

CONTRIBUTING.md

@@ -38,11 +38,11 @@ class toIteratorVsIterator(xs: Iterable[Int]) {
 }
 ~~~
 
-3. Add a corresponding file in the `scalafix/output213/src/main/scala/fix/` directory
+3. Add a corresponding file in the `scalafix/output/src/main/scala/fix/` directory
    with the same code but using the strawman:
 
 ~~~ scala
-import strawman.collection.Iterable
+import scala.collection.compat._
 
 class toIteratorVsIterator(xs: Iterable[Int]) {
   xs.iterator
@@ -75,3 +75,43 @@ Fix the implementation of the rule (in the
 `rules/src/main/scala/fix/NewCollections.scala` file) until the
 tests are green. You can find more help about the scalafix API in its
 [documentation](https://scalacenter.github.io/scalafix/docs/rule-authors/setup).
+
+
+### Scalafix Teskit Directory Layout
+
+```
+.
+├── data                    |
+│   └── src                 |
+│       └── main            |
+│           └── scala       | Project to avoid duplicating code between input and output
+├── input                   |
+│   └── src                 |
+│       └── main            |
+│           ├── scala       | Input that cross-compile
+│           └── scala-2.12  | 2.12 specific input
+├── output                  |
+│   └── src                 |
+│       └── main            |
+│           └── scala       | Output that cross-compile
+├── output212               |
+│   └── src                 |
+│       └── main            |
+│           └── scala-2.12  | 2.12 specific output
+├── output213               |
+│   └── src                 |
+│       └── main            |
+│           └── scala       | 2.13 specific output (from a cross-compiled input)
+├── output213-failure       |
+│   └── src                 |
+│       └── main            |
+│           └── scala       | 2.13 specific output that cannot be migrated due to technical limitations
+├── rules                   |
+│   └── src                 |
+│       └── main            |
+│           └── scala       | Rule implementations
+└── tests                   |
+    └── src                 |
+        └── test            |
+            └── scala       | Scalafix testkit launcher (useful to run a single input file)
+```

build.sbt

@@ -131,7 +131,6 @@ lazy val `scalafix-rules` = project
   )
 
 // == Scalafix Test Setup ==
-
 lazy val sharedScalafixSettings = Seq(
   scalacOptions ++= Seq(
     "-deprecation",
@@ -162,7 +161,6 @@ lazy val `scalafix-input` = project
   )
   .dependsOn(`scalafix-data212`)
 
-
 val `scalafix-output` = MultiScalaProject("scalafix-output", "scalafix/output",
   _.settings(sharedScalafixSettings)
    .settings(dontPublish)
@@ -194,16 +192,12 @@ lazy val `scalafix-tests` = project
     libraryDependencies += "ch.epfl.scala" % "scalafix-testkit" % scalafixVersion % Test cross CrossVersion.full,
     buildInfoPackage := "fix",
     buildInfoKeys := Seq[BuildInfoKey](
-      "inputSourceroot" ->
-        sourceDirectory.in(`scalafix-input`, Compile).value,
-      "outputSourceroot" ->
-        (baseDirectory in ThisBuild).value / "scalafix/output/src/main",
-      "output212Sourceroot" -> output212.value,
-      "output213Sourceroot" -> output213.value,
-      "output213FailureSourceroot" ->
-        sourceDirectory.in(`scalafix-output213-failure`, Compile).value,
-      "inputClassdirectory" ->
-        classDirectory.in(`scalafix-input`, Compile).value
+      "inputSourceroot"            -> sourceDirectory.in(`scalafix-input`, Compile).value,
+      "outputSourceroot"           -> (baseDirectory in ThisBuild).value / "scalafix/output/src/main",
+      "output212Sourceroot"        -> output212.value,
+      "output213Sourceroot"        -> output213.value,
+      "output213FailureSourceroot" -> sourceDirectory.in(`scalafix-output213-failure`, Compile).value,
+      "inputClassdirectory"        -> classDirectory.in(`scalafix-input`, Compile).value
     ),
     test in Test := (test in Test).dependsOn(
       compile in (`scalafix-output211`, Compile),

project/MultiScalaProject.scala

@@ -8,6 +8,24 @@ import scalajscrossproject.ScalaJSCrossPlugin.autoImport._
 
 import java.io.File
 
+/** MultiScalaCrossProject and MultiScalaProject are an alternative to crossScalaVersion
+  * it allows you to create a template for a sbt project you can instanciate with a
+  * specific scala version.
+  *
+  * {{{
+  * // create a project template
+  * val myProject = MultiScalaProject(
+  *   "name",
+  *   "path/to/dir",
+  *   _.settings(...) // Project => Project (scala version independent configurations)
+  * )
+  *
+  * // instanciate a sbt project
+  * lazy val myProject211 = myProject("2.11.12", _.settings(...) /* scala version dependent configurations */)
+  * lazy val myProject212 = myProject("2.12.6" , _.settings(...))
+  * // ...
+  * }}}
+  */
 trait MultiScala {
   def majorMinor(in: String): String = {
     val Array(major, minor, _) = in.split("\\.")
@@ -101,21 +119,3 @@ class MultiScalaProject(
     configurePerScala(configure(resultingProject))
   }
 }
-
-object TestProject {
-  private def base(sub: String): String =
-    s"scalafix/$sub"
-
-  def apply(
-      sub: String,
-      configure: (Project, String) => Project): MultiScalaProject =
-    apply(sub, project => configure(project, s"${base(sub)}/src/main"))
-
-  def apply(sub: String, configure: Project => Project): MultiScalaProject =
-    MultiScalaProject(
-      s"tests${sub.capitalize}",
-      base(sub),
-      configure.andThen(_.disablePlugins(scalafix.sbt.ScalafixPlugin))
-    )
-
-}