Move s.u.FromString to s.u.CommandLineParser.FromString.

There are many competing ways to parse things. `FromString` is
tailored for command-line parsing. As such we should not expose it
with a general name like `scala.util.FromString`. Instead, we move
it inside `CommandLineParser` to make it clear that it is meant for
command-line parsing.

Author: sjrd

library/src/scala/util/CommandLineParser.scala

@@ -41,4 +41,49 @@ object CommandLineParser {
       else s" after ${err.idx} arguments"
     println(s"Illegal command line$where: ${err.msg}")
   }
+
+  trait FromString[T] {
+    /** Can throw java.lang.IllegalArgumentException */
+    def fromString(s: String): T
+
+    def fromStringOption(s: String): Option[T] =
+      try Some(fromString(s))
+      catch {
+        case ex: IllegalArgumentException => None
+      }
+  }
+
+  object FromString {
+    given FromString[String] {
+      def fromString(s: String) = s
+    }
+
+    given FromString[Boolean] {
+      def fromString(s: String) = s.toBoolean
+    }
+
+    given FromString[Byte] {
+      def fromString(s: String) = s.toByte
+    }
+
+    given FromString[Short] {
+      def fromString(s: String) = s.toShort
+    }
+
+    given FromString[Int] {
+      def fromString(s: String) = s.toInt
+    }
+
+    given FromString[Long] {
+      def fromString(s: String) = s.toLong
+    }
+
+    given FromString[Float] {
+      def fromString(s: String) = s.toFloat
+    }
+
+    given FromString[Double] {
+      def fromString(s: String) = s.toDouble
+    }
+  }
 }

library/src/scala/util/FromString.scala

@@ -8,6 +8,6 @@ class Foo {
 
 @main def g(x: Int*)(y: Int*) = () // error: varargs parameter of @main method must come last
 
-@main def h[T: util.FromString](x: T) = () // error: @main method cannot have type parameters
+@main def h[T: util.CommandLineParser.FromString](x: T) = () // error: @main method cannot have type parameters
 
 @main def i(x: Int)(using Foo) = () // error: @main method cannot have implicit parameters

tests/neg/main-functions2.scala

@@ -13,7 +13,7 @@ import collection.mutable
  */
 trait MainAnnotation extends StaticAnnotation:
 
-  /** The class used for argument string parsing. E.g. `scala.util.FromString`,
+  /** The class used for argument string parsing. E.g. `scala.util.CommandLineParser.FromString`,
    *  but could be something else
    */
   type ArgumentParser[T]
@@ -44,7 +44,7 @@ end MainAnnotation
 
 class main extends MainAnnotation:
 
-  type ArgumentParser[T] = util.FromString[T]
+  type ArgumentParser[T] = util.CommandLineParser.FromString[T]
   type MainResultType = Any
 
   def command(args: Array[String]): Command = new Command:
@@ -202,4 +202,4 @@ Error: invalid argument for num: binary
 Error: unused argument: 01
 Usage: add num inc?
 
-*/
+*/

tests/pos/main-method-scheme-class-based.scala

@@ -22,7 +22,7 @@ class main(progName: String, args: Array[String], docComment: String) extends Ma
 
   def this() = this("", Array(), "")
 
-  type ArgumentParser[T] = util.FromString[T]
+  type ArgumentParser[T] = util.CommandLineParser.FromString[T]
 
   /** A buffer of demanded argument names, plus
    *   "?"  if it has a default
@@ -167,4 +167,4 @@ Error: unknown argument name: --foo
 Usage: add num inc?
 Adds two numbers
 
-*/
+*/

tests/pos/main-method-scheme.scala

@@ -5,7 +5,7 @@ import collection.mutable
  */
 class main extends EntryPoint.Annotation:
 
-  type ArgumentParser[T] = util.FromString[T]
+  type ArgumentParser[T] = util.CommandLineParser.FromString[T]
   type EntryPointResult  = Unit
 
   inline def wrapperName(entryPointName: String): String =