Create docs.scala-lang.org/scala3/guides/reference and move language-versions here

Content was taken from commit 270bd8b0f5af338be73790082d774516a83a73b5

Author: julienrf

_config.yml

@@ -123,6 +123,15 @@ defaults:
       overview-name: "Macros in Scala 3"
       layout: multipage-overview
       permalink: "/scala3/guides/macros/:title.html"
+  -
+    scope:
+      path: "_overviews/scala3-reference"
+    values:
+      scala3: true
+      partof: scala3-reference
+      overview-name: "Scala 3 Language Reference"
+      layout: multipage-overview
+      permalink: "/scala3/guides/reference/:title.html"
   -
     scope:
       path: "scala3"
@@ -133,7 +142,7 @@ defaults:
 highlighter: rouge
 permalink: /:categories/:title.html:output_ext
 baseurl:
-scala3ref: "https://dotty.epfl.ch/docs/reference"
+scala3ref: "/scala3/guides/reference"
 exclude: ["vendor"]
 plugins:
   - jekyll-redirect-from

_overviews/scala3-reference/language-versions.md

@@ -0,0 +1,36 @@
+---
+title: Language Versions
+type: chapter
+description: This page lists the different flavours of language supported by the Scala 3 compiler.
+num: 2
+previous-page: overview
+---
+
+The default Scala language version currently supported by the Dotty compiler is `3.0`. There are also other language versions that can be specified instead:
+
+- `3.0-migration`: Same as `3.0` but with a Scala 2 compatibility mode that helps moving Scala 2.13 sources over to Scala 3. In particular, it
+
+    - flags some Scala 2 constructs that are disallowed in Scala 3 as migration warnings instead of hard errors,
+    - changes some rules to be more lenient and backwards compatible with Scala 2.13
+    - gives some additional warnings where the semantics has changed between Scala 2.13 and 3.0
+    - in conjunction with `-rewrite`, offer code rewrites from Scala 2.13 to 3.0.
+
+- `future`: A preview of changes introduced in the next versions after 3.0. In the doc pages here we refer to the language version with these changes as `3.1`, but it might be that some of these changes will be rolled out in later `3.x` versions.
+
+Some Scala-2 specific idioms will be dropped in this version. The feature set supported by this version will be refined over time  as we approach its release.
+
+- `future-migration`: Same as `future` but with additional helpers to migrate from `3.0`. Similarly to the helpers available under `3.0-migration`, these include migration warnings and optional rewrites.
+
+There are two ways to specify a language version.
+
+- With a `-source` command line setting, e.g. `-source 3.0-migration`.
+- With a `scala.language` import at the top of a source file, e.g:
+
+```scala
+package p
+import scala.language.`future-migration`
+
+class C { ... }
+```
+
+Language imports supersede command-line settings in the source files where they are specified. Only one language import specifying a source version is allowed in a source file, and it must come before any definitions in that file.

_overviews/scala3-reference/overview.md

@@ -0,0 +1,7 @@
+---
+title: Overview
+type: chapter
+description: This page begins the reference documentation.
+num: 1
+next-page: language-versions
+---

scala3/guides.md

@@ -18,6 +18,10 @@ guides:
     icon: birthday-cake
     url: "/scala3/guides/tasty-overview.html"
     description: "An overview over the TASTy format aimed at end-users of the Scala language."
+  - title: Scala 3 Language Reference
+    icon: book
+    url: "/scala3/guides/reference/overview.html"
+    description: "The reference for Scala 3"
 ---
 
 <section class="full-width">