Better support for nullability in Option.apply and drop Option.fromNullable (#24238)

Yes, this is not the most ideal signature for `Option.apply` but it
allows at least to drop `Option.fromNullable` and an easier migration to
explicit nulls (no need to add `fromNullable` everywhere).

Superseed #24231 in the sense where we focus here on the nullability
issue rather than the more global issue.

Reverts #24230
Relates to #24206

Author: hamzaremmal

compiler/src/dotty/tools/dotc/transform/localopt/FormatChecker.scala

@@ -126,7 +126,7 @@ class TypedFormatChecker(partsElems: List[Tree], parts: List[String], args: List
     def at(g: SpecGroup): Int = descriptor.start(g.ordinal)
     def end(g: SpecGroup): Int = descriptor.end(g.ordinal)
     def offset(g: SpecGroup, i: Int = 0): Int = at(g) + i
-    def group(g: SpecGroup): Option[String] = Option(descriptor.group(g.ordinal)).asInstanceOf[Option[String]]
+    def group(g: SpecGroup): Option[String] = Option(descriptor.group(g.ordinal))
     def stringOf(g: SpecGroup): String = group(g).getOrElse("")
     def intOf(g: SpecGroup): Option[Int] = group(g).map(_.toInt)
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1922,7 +1922,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         NoType
     }
 
-    pt match {
+    pt.stripNull() match {
       case pt: TypeVar
       if untpd.isFunctionWithUnknownParamType(tree) && !calleeType.exists =>
         // try to instantiate `pt` if this is possible. If it does not

library/src/scala/Option.scala

@@ -28,7 +28,7 @@ object Option {
    *  @param  x the value
    *  @return   Some(value) if value != null, None if value == null
    */
-  def apply[A](x: A): Option[A] = if (x == null) None else Some(x)
+  def apply[A](x: A | Null): Option[A] = if (x == null) None else Some(x)
 
   /** An Option factory which returns `None` in a manner consistent with
    *  the collections hierarchy.

library/src/scala/Predef.scala

@@ -594,10 +594,6 @@ object Predef extends LowPriorityImplicits {
     inline infix def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)
 
-  extension (opt: Option.type)
-    @experimental
-    inline def fromNullable[T](t: T | Null): Option[T] = Option(t).asInstanceOf[Option[T]]
-
   /** A type supporting Self-based type classes.
    *
    *    A is TC

library/src/scala/concurrent/impl/Promise.scala

@@ -275,7 +275,7 @@ private[concurrent] object Promise {
 
     override final def isCompleted: Boolean = value0 ne null
 
-    override final def value: Option[Try[T]] = Option(value0).asInstanceOf[Option[Try[T]]]
+    override final def value: Option[Try[T]] = Option(value0)
 
     @tailrec // returns null if not completed
     private final def value0: Try[T] | Null = {

library/src/scala/quoted/FromExpr.scala

@@ -104,7 +104,7 @@ object FromExpr {
    */
   given OptionFromExpr[T](using Type[T], FromExpr[T]): FromExpr[Option[T]] with {
     def unapply(x: Expr[Option[T]])(using Quotes) = x match {
-      case '{ Option[T](${Expr(y)}) } => Some(Option(y))
+      case '{ Option[T](${Expr(y)}: T) } => Some(Option(y))
       case '{ None } => Some(None)
       case '{ ${Expr(opt)} : Some[T] } => Some(opt)
       case _ => None

library/src/scala/runtime/stdLibPatches/Predef.scala

@@ -66,10 +66,6 @@ object Predef:
     inline infix def ne(inline y: AnyRef | Null): Boolean =
       !(x eq y)
 
-  extension (opt: Option.type)
-    @experimental
-    inline def fromNullable[T](t: T | Null): Option[T] = Option(t).asInstanceOf[Option[T]]
-
   /** A type supporting Self-based type classes.
    *
    *    A is TC

scaladoc/src/dotty/tools/scaladoc/SourceLinks.scala

@@ -74,8 +74,8 @@ class SourceLinkParser(revision: Option[String]) extends ArgParser[SourceLink]:
         else Right(TemplateSourceLink(supported.foldLeft(string)((template, pattern) =>
           template.replace(pattern, SupportedScalaDocPatternReplacements(pattern)))))
       case KnownProvider(name: String, organization: String, repo: String, rawRevision, rawSubPath) =>
-        val subPath = Option.fromNullable(rawSubPath).fold("")("/" + _.drop(1))
-        val pathRev = Option.fromNullable(rawRevision).map(_.drop(1)).orElse(revision)
+        val subPath = Option(rawSubPath).fold("")("/" + _.drop(1))
+        val pathRev = Option(rawRevision).map(_.drop(1)).orElse(revision)
 
         def withRevision(template: String => SourceLink) =
           pathRev.fold(Left(s"No revision provided"))(r => Right(template(r)))

scaladoc/src/dotty/tools/scaladoc/site/StaticSiteLoader.scala

@@ -116,8 +116,8 @@ class StaticSiteLoader(val root: File, val args: Scaladoc.Args)(using StaticSite
 
   def loadBlog(): Option[LoadedTemplate] = {
     val blogConfig = BlogParser.readYml(root)
-    val rootPath = Option.fromNullable(blogConfig.input).map(input => ctx.resolveNewBlogPath(input)).getOrElse(ctx.blogPath)
-    val defaultDirectory = Option.fromNullable(blogConfig.output).getOrElse("blog")
+    val rootPath = Option(blogConfig.input).map(input => ctx.resolveNewBlogPath(input)).getOrElse(ctx.blogPath)
+    val defaultDirectory = Option(blogConfig.output).getOrElse("blog")
 
     type Date = (String, String, String)
     if (!Files.exists(rootPath) || blogConfig.hidden) None

scaladoc/src/dotty/tools/scaladoc/tasty/SymOps.scala

@@ -277,7 +277,7 @@ class SymOpsWithLinkCache:
               then externalLinkCache(csym.associatedFile)
               else {
                 def calculatePath(file: AbstractFile): String = file.underlyingSource.filter(_ != file).fold("")(f => calculatePath(f) + "/") + file.path
-                val calculatedLink = Option.fromNullable(csym.associatedFile).map(f => calculatePath(f)).flatMap { path =>
+                val calculatedLink = Option(csym.associatedFile).map(f => calculatePath(f)).flatMap { path =>
                   dctx.externalDocumentationLinks.find(_.originRegexes.exists(r => r.matches(path)))
                 }
                 externalLinkCache += (csym.associatedFile -> calculatedLink)