SI-6879 improves Context.freshName

Instead of per-compilation unit unique counters, the freshName API now
uses a per-Global counter. Fresh names now also contain dollars to exclude
clashes with supported user-defined names (the ones without dollar signs).

This doesn’t fix the bug, because per-Global counters get created anew
every time a new Global is instantiated, and that provides some potential
for name clashes even for def macros, but at least it completely excludes
clashes in typical situations.

1 files changed, 22 insertions, 6 deletions

diff --git a/src/compiler/scala/reflect/macros/contexts/Names.scala b/src/compiler/scala/reflect/macros/contexts/Names.scala
index c2f14cf0f1..299af40b94 100644
--- a/src/compiler/scala/reflect/macros/contexts/Names.scala
+++ b/src/compiler/scala/reflect/macros/contexts/Names.scala
@@ -4,7 +4,9 @@ package contexts
 trait Names {
   self: Context =>
 
-  def freshNameCreator = callsiteTyper.context.unit.fresh
+  import global._
+
+  def freshNameCreator = globalFreshNameCreator
 
   def fresh(): String =
     freshName()
@@ -16,11 +18,25 @@ trait Names {
     freshName[NameType](name)
 
   def freshName(): String =
-    freshName("fresh$")
-
-  def freshName(name: String): String =
-    freshNameCreator.newName(name)
+    freshName(nme.FRESH_PREFIX)
+
+  def freshName(name: String): String = {
+    // In comparison with the first version of freshName, current "fresh" names
+    // at least can't clash with legible user-written identifiers and are much less likely to clash with each other.
+    // It is still not good enough however, because the counter gets reset every time we create a new Global.
+    //
+    // This would most certainly cause problems if Scala featured something like introduceTopLevel,
+    // but even for def macros this can lead to unexpected troubles. Imagine that one Global
+    // creates a term of an anonymous type with a member featuring a "fresh" name, and then another Global
+    // imports that term with a wildcard and then generates a "fresh" name of its own. Given unlucky
+    // circumstances these "fresh" names might end up clashing.
+    //
+    // TODO: hopefully SI-7823 will provide an ultimate answer to this problem.
+    // In the meanwhile I will also keep open the original issue: SI-6879 "c.freshName is broken".
+    val sortOfUniqueSuffix = freshNameCreator.newName(nme.FRESH_SUFFIX)
+    name + "$" + sortOfUniqueSuffix
+  }
 
   def freshName[NameType <: Name](name: NameType): NameType =
-    name.mapName(freshNameCreator.newName(_)).asInstanceOf[NameType]
+    name.mapName(freshName(_)).asInstanceOf[NameType]
 }
\ No newline at end of file