Move sliceToTermName logic to Decorators

That way we can keep Contexts out of Names.

Author: odersky

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -5,7 +5,7 @@ package config
 import core._
 import Contexts._, Symbols._, Names._, NameOps._, Phases._
 import StdNames.nme
-import Decorators.{given _}
+import Decorators.{_, given _}
 import util.SrcPos
 import SourceVersion._
 import reporting.Message

compiler/src/dotty/tools/dotc/config/SourceVersion.scala

@@ -5,7 +5,7 @@ package config
 import core.Contexts._
 import core.Names.TermName
 import core.StdNames.nme
-import core.Decorators.{given _}
+import core.Decorators.{_, given _}
 import util.Property
 
 enum SourceVersion:

compiler/src/dotty/tools/dotc/core/Decorators.scala

@@ -20,22 +20,34 @@ object Decorators {
    *  with a normal wildcard. In the future, once #9255 is in trunk, replace with
    *  a simple collective extension.
    */
-  implicit object PreNamedString:
-    extension (pn: PreName) def toTypeName: TypeName = pn match
-      case s: String => typeName(s)
-      case n: Name => n.toTypeName
-    extension (pn: PreName) def toTermName: TermName = pn match
+  extension (pn: PreName)
+    def toTermName: TermName = pn match
       case s: String => termName(s)
       case n: Name => n.toTermName
+    def toTypeName: TypeName = pn match
+      case s: String => typeName(s)
+      case n: Name => n.toTypeName
 
   extension (s: String):
-    def splitWhere(f: Char => Boolean, doDropIndex: Boolean): Option[(String, String)] = {
+    def splitWhere(f: Char => Boolean, doDropIndex: Boolean): Option[(String, String)] =
       def splitAt(idx: Int, doDropIndex: Boolean): Option[(String, String)] =
         if (idx == -1) None
         else Some((s.take(idx), s.drop(if (doDropIndex) idx + 1 else idx)))
-
       splitAt(s.indexWhere(f), doDropIndex)
-    }
+
+    /** Create a term name from a string slice, using a common buffer.
+     *  This avoids some allocation relative to `termName(s)`
+     */
+    def sliceToTermName(start: Int, end: Int)(using Context): SimpleName =
+      val base = ctx.base
+      val len = end - start
+      while len > base.nameCharBuffer.length do
+        base.nameCharBuffer = new Array[Char](base.nameCharBuffer.length * 2)
+      s.getChars(start, end, base.nameCharBuffer, 0)
+      termName(base.nameCharBuffer, 0, len)
+
+    def sliceToTypeName(start: Int, end: Int)(using Context): TypeName =
+      sliceToTermName(start, end).toTypeName
 
   /** Implements a findSymbol method on iterators of Symbols that
    *  works like find but avoids Option, replacing None with NoSymbol.

compiler/src/dotty/tools/dotc/core/Names.scala

@@ -11,7 +11,6 @@ import scala.internal.Chars.isIdentifierStart
 import collection.immutable
 import config.Config
 import java.util.HashMap
-import Contexts.{Context, ctx}
 
 import scala.annotation.internal.sharable
 
@@ -640,33 +639,14 @@ object Names {
     termName(bs, offset, len).toTypeName
 
   /** Create a term name from a string.
-   *  See `termName(s: String, from: Int, len: Int) for a more efficient version
-   *  which however requires a Context for its operation
+   *  See `sliceToTermName` in `Decorators` for a more efficient version
+   *  which however requires a Context for its operation.
    */
   def termName(s: String): SimpleName = termName(s.toCharArray, 0, s.length)
 
   /** Create a type name from a string */
   def typeName(s: String): TypeName = typeName(s.toCharArray, 0, s.length)
 
-  /** Create a term name from a string slice, using a common buffer.
-   *  This avoids some allocation relative to `termName(s: String)`
-   */
-  def termName(s: String, from: Int, len: Int)(using ctx: Contexts.Context): TermName = {
-    val base = ctx.base
-
-    while (len > base.nameCharBuffer.length)
-      base.nameCharBuffer = new Array[Char](base.nameCharBuffer.length * 2)
-
-    s.getChars(from, from + len, base.nameCharBuffer, 0)
-    termName(base.nameCharBuffer, 0, len)
-  }
-
-  /** Create a type name from a string slice, using a common buffer.
-   *  This avoids some allocation relative to `typeName(s: String)`
-   */
-  def typeName(s: String, from: Int, len: Int)(using Context): TypeName =
-    termName(s, from, len).toTypeName
-
   table(0) = new SimpleName(-1, 0, null)
 
   /** The term name represented by the empty string */

compiler/src/dotty/tools/dotc/core/SymbolLoaders.scala

@@ -205,7 +205,7 @@ object SymbolLoaders {
     src.lastModified >= bin.lastModified
 
   private def nameOf(classRep: ClassRepresentation)(using Context): TermName =
-    termName(classRep.fileName, 0, classRep.nameLength)
+    classRep.fileName.sliceToTermName(0, classRep.nameLength)
 
   /** Load contents of a package
    */