Add slides about the Scala 3 migration course

slides/99-scala3-migration-course.md

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+## &#173;
+## &#173;
+## &#173;
+## Scala 3 migration course
+
+---
+
+## Course overview
+## &#173;
+
+* In this course we will:
+    * Start from an existing sbt build (Scala 2.13)
+    * Use sbt-scala3-migrate to migrate the build to Scala 3
+### &#173;
+* The objective is to learn the four steps of migrating a project:
+    * Updating the dependencies
+    * Updating the compiler options
+    * Patching the syntax of the code
+    * Fixing the type inference errors
+
+
+
+---
+
+## Dotty/Scala 3
+## &#173;
+
+* Dotty: New research project started in 2012 by Martin Odersky's lab at EPFL
+* Dotty announced to become Scala 3 (April 2018)
+* 3.0.0 released on May 13, 2021
+* [3.3.0](https://github.com/lampepfl/dotty/releases/tag/3.3.0) relased on May 30th, 2023. First LTS (Long Term Support) release.
+* IDE support
+    * [Visual Studio Code](https://code.visualstudio.com) with [Metals](https://scalameta.org/metals/)
+        * integrated support in Metals including Scala Worksheet support!
+    * [IntelliJ](https://www.jetbrains.com/idea/)
+        * Scala 3 support with the [Scala Plugin](https://lp.jetbrains.com/intellij-scala/)
+* There's the [Scala 3 Migration Guide](https://docs.scala-lang.org/scala3/guides/migration/compatibility-intro.html)!
+
+---
+## Compatibility in Scala 2
+## &#173;
+
+- Before Scala 2.10: no compatibility between any two versions
+  - Different standard library
+  - Different binary interface
+- Since Scala 2.10: strict binary compatibility in minor versions
+  - 2.13.11 is compatible with 2.13.8
+  - 2.13.11 is not compatible with 2.12.19
+
+## &#173;
+### => Ecosystem jump between 2.12 and 2.13
+
+---
+
+## Compatibility between Scala 2.13 and Scala 3
+## &#173;
+
+* Scala 3 uses the Scala 2.13 standard library
+* Scala 3 produces Scala 2.13 compatible binaries (class files, sjsir, ...)
+* Scala 3 can read Scala 2.13 signatures (Pickle format)
+* Scala 2.13 can read Scala 3 signatures (TASTy) using -Ytasty-reader
+
+## &#173;
+
+### => Backward and forward compatibility between Scala 2.13 and Scala 3
+
+---
+
+## For 3 use 2.13
+## &#173;
+
+![](images/compatibility-3-to-213.svg)
+
+```
+lazy val foo = project.in(file("foo"))
+  .settings(
+    scalaVersion := "3.0.0",
+    libraryDependencies +=
+      ("org.bar" %% "bar" % "1.0.0").cross(CrossVersion.for3Use2_13)
+  )
+```
+
+---
+
+## For 2.13 use 3 (TASTy reader)
+## &#173;
+
+![](images/compatibility-213-to-3.svg)
+
+```
+lazy val foo = project.in(ile("foo"))
+  .settings(
+    scalaVersion := "2.13.6",
+    scalacOptions += "-Ytasty-reader",
+    libraryDependencies += 
+      ("org.bar" %% "bar" % "1.0.0").cross(CrossVersion.for2_13Use3)
+  )
+```
+
+---
+
+## The sandwich pattern
+## &#173;
+
+![](images/compatibility-sandwich.svg)
+
+---
+
+## The diamond pattern
+## &#173;
+
+<img src="images/compatibility-diamond.png" width="500"/>
+
+```
+[error] Modules were resolved with conflicting cross-version suffixes in main:
+[error]    org.typelevel:cats _3, _2.13
+```
+
+---
+
+## Metaprogramming
+## &#173;
+
+- Scala 2.13 macros are experimental
+- Scala 3 macros are based on new foundations.
+They are simpler and more stable.
+- Scala 2.13 and Scala 3 macros are incompatible
+- The community started migrating the macro libraries to Scala 3.
+See [Table of macro libraries.](https://scalacenter.github.io/scala-3-migration-guide/docs/macros/macro-libraries.html)
+
+---
+
+## Compiler plugins
+## &#173;
+
+- The Scala 3 compiler is completely new
+- Scala 2.13 plugins cannot be used in Scala 3
+- Scala 3 plugins are more constrained
+- Some important plugins were integrated in the compiler, and can be activated with an option:
+  - `-Ykind-projector`
+  - `-scalajs`
+  - `-semanticdb`
+
+---
+## Compiler Options (`scalacOptions`)
+## &#173;
+
+- Most options are available
+- Some are renamed
+- Some are dropped
+- Some of the most used Scala 2 options are ported to Scala 3. For example, we ported `-Wunused` to Scala 3.3.0.
+- See [table of compiler options](https://docs.scala-lang.org/scala3/guides/migration/options-lookup.html).
+
+---
+## Syntactic changes
+
+![](images/incompat-syntax.png)
+
+---
+
+## Dropped features
+
+![](images/incompat-dropped-features.png)
+---
+
+## Contextual abstractions (Implicits)
+
+![](images/incompat-context-abstractions.png)
+
+---
+
+## Other changed features
+
+![](images/incompat-changed-features.png)
+
+---
+
+## Type checker and type inference
+
+![](images/incompat-types.png)
+
+---
+
+## sbt-scala3-migrate
+
+- It's an sbt plugin
+
+![](images/sbt-scala3-migrate-install.png)
+
+- It can assist you during the migration to Scala 3 of your build
+
+![](images/sbt-scala3-migrate-welcome.png)
+
+---
+
+## Scala 3 migration course
+
+![](images/scalacenter-scala3-migration-course.png)
+
+---
+
+## Scala 3 migration course
+## &#173;
+
+```
+$ cmtc install -f -s scalacenter/scala3-migration-course
+Downloading studentified course from 'https://github.com/scalacenter/scala3-migration-course/releases/download/0.1.0/scala3-migrate-course-student.zip' to courses directory
+
+Project scalacenter/scala3-migration-course (0.1.0) successfully installed to:
+  /home/user/Library/Caches/com.lunatech.cmt/Courses/scala3-migration-course
+
+Current course set to '/home/user/Library/Caches/com.lunatech.cmt/Courses/scala3-migration-course'
+
+Exercises in repository:
+  1.  *   exercise_000_initial_state
+  2.      exercise_001_install_sbt_scala3_migrate
+  3.      exercise_002_migrate_dependencies
+  4.      exercise_003_migrate_scalac_options
+  5.      exercise_004_migrate_syntax
+  6.      exercise_005_migrate_types
+  7.      exercise_006_update_scala_version
+```