Support auto-possessification of nested quantifiers

Author: natecook1000

Sources/_StringProcessing/Regex/DSLList.swift

@@ -216,10 +216,17 @@ extension DSLList {
 
     switch nodes[position] {
     case .quantification(let amount, _, _):
+      let quantPosition = position
       position += 1
+      
+      // Do a search within this quantification's contents
+      // FIXME: How to handle an inner quantification surfacing here?
+      var innerPosition = position
+      _ = autoPossessifyNextQuantification(&innerPosition)
+      
       switch _requiredAtomImpl(&position) {
       case .some(let atom?):
-        return (position - 1, atom)
+        return (quantPosition, atom)
       case .none, .some(.none):
         return nil
       }

Tests/RegexTests/OptimizationTests.swift

@@ -31,7 +31,7 @@ import Testing
   }
 
   @available(macOS 9999, *)
-  @Test(arguments: [#/a+b/#, #/a*b/#, #/\w+\s/#, #/(?:a+b|b+a)/#]) // , #/\d+a/#
+  @Test(arguments: [#/a+b/#, #/a*b/#, #/\w+\s/#, #/(?:a+b|b+a)/#, #/(?:(?:a+b)+b)/#])
   func autoPossessify(pattern: Regex<Substring>) throws {
     var list = DSLList(tree: pattern.program.tree)
     list.autoPossessify()