Allow Str.split to take more than one needle

This should make most of the cases that Text::CSV handles a *lot* faster.

src/core/Str.pm

@@ -1017,6 +1017,94 @@ my class Str does Stringy { # declared in BOOTSTRAP
             }.new(self,$limit));
         }
     }
+    multi method split(Str:D \string, @needles;; :$all, :$keep-indices) {
+        return self.split(string,rx/ @needles /,:$all)
+          if Rakudo::Internals.NOT_ALL_DEFINED_TYPE(@needles,Cool);
+
+        my str $str       = nqp::unbox_s(string);
+        my $positions    := nqp::list;
+        my $needles      := nqp::list;
+        my $needle-chars := nqp::list;
+        my $sorted       := nqp::list;
+        my int $found     = -1;
+        my $fired;
+        for @needles.kv -> $needle-index, $needle {
+            my str $need  = nqp::unbox_s($needle.Str);
+            my int $chars = nqp::chars($need);
+            nqp::push($needles,$need);
+            nqp::push($needle-chars,$chars);
+
+            my int $pos;
+            my int $i;
+            my int $seen = nqp::elems($positions);
+            while nqp::isge_i($i = nqp::index($str, $need, $pos),0) {
+                nqp::push($positions,Pair.new($i,nqp::unbox_i($needle-index)));
+                nqp::push($sorted,nqp::unbox_i($found = $found + 1));
+                $pos = $i + $chars;
+            }
+            $fired = $fired + 1 if nqp::elems($positions) > $seen;
+        }
+
+        nqp::p6sort($sorted, -> int $a, int $b {
+            # $a <=> $b || $b.chars <=> $a.chars, aka pos asc, length desc
+            nqp::getattr(nqp::atpos($positions,$a),Pair,'$!key')
+              <=> nqp::getattr(nqp::atpos($positions,$b),Pair,'$!key')
+                || nqp::atpos($needle-chars,
+                     nqp::getattr(nqp::atpos($positions,$b),Pair,'$!value'))
+                       <=> nqp::atpos($needle-chars,
+                         nqp::getattr(nqp::atpos($positions,$a),Pair,'$!value'))
+        }) if $fired > 1;
+
+        my $pair;
+        my int $from;
+        my int $needle-index;
+        my int $pos;
+        my $result := nqp::list;
+        if $keep-indices {
+            while nqp::elems($sorted) {
+                $pair := nqp::atpos($positions,nqp::shift($sorted));
+                $from  = nqp::getattr($pair,Pair,'$!key');
+                if nqp::isge_i($from,$pos) { # not hidden by other needle
+                    $needle-index = nqp::getattr($pair,Pair,'$!value');
+                    nqp::push($result,nqp::substr($str,$pos,$from - $pos));
+                    nqp::push($result,$needle-index);
+                    $pos = $from + nqp::atpos($needle-chars,$needle-index);
+                }
+            }
+        }
+        elsif $all {
+            while nqp::elems($sorted) {
+                $pair := nqp::atpos($positions,nqp::shift($sorted));
+                $from  = nqp::getattr($pair,Pair,'$!key');
+                if nqp::isge_i($from,$pos) { # not hidden by other needle
+                    $needle-index = nqp::getattr($pair,Pair,'$!value');
+                    nqp::push($result,nqp::substr($str,$pos,$from - $pos));
+                    nqp::push($result,nqp::atpos($needles,$needle-index));
+                    $pos = $from + nqp::atpos($needle-chars,$needle-index);
+                }
+            }
+        }
+        else {
+            while nqp::elems($sorted) {
+                $pair := nqp::atpos($positions,nqp::shift($sorted));
+                $from  = nqp::getattr($pair,Pair,'$!key');
+                if nqp::isge_i($from,$pos) { # not hidden by other needle
+                    nqp::push($result,nqp::substr($str,$pos,$from - $pos));
+                    $pos = $from + nqp::atpos(
+                      $needle-chars,nqp::getattr($pair,Pair,'$!value'));
+                }
+            }
+        }
+        nqp::push($result,nqp::substr($str,$pos));
+
+        $result
+    }
+    multi method split(Str:D \string,@needles,$parts;; :$all, :$keep-indices) {
+        my @result = self.split(string,@needles,:$all,:$keep-indices);
+        nqp::istype($parts,Whatever) || $parts === Inf
+          ?? @result
+          !! @result.head($all || $keep-indices ?? $parts + $parts !! $parts)
+    }
 
     method samecase(Str:D: Str $pattern) {
         my str $str = nqp::unbox_s(self);