From f809b066ba220568921f611e652301590abb0b3a Mon Sep 17 00:00:00 2001
From: Tomas Janousek <tomi@nomi.cz>
Date: Tue, 4 Aug 2015 16:12:50 +0200
Subject: [PATCH 1/2] Fix packrat caching with PagedSeqReader

This fixes #45.

The problem was that whenever PagedSeqReader is constructed, source is
assigned seq (although lazily) but since PagedSeq is not a subclass of
java.lang.CharSequence, an implicit conversion takes place via
Predef#SeqCharSequence, creating a new object. The problem is that this
happens every time PagedSeqReader#rest or drop is called, breaking packrat
caching entirely.
---
 .../scala/util/parsing/input/PagedSeqReader.scala    | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/main/scala/scala/util/parsing/input/PagedSeqReader.scala b/src/main/scala/scala/util/parsing/input/PagedSeqReader.scala
index 500c80c7..51e66943 100644
--- a/src/main/scala/scala/util/parsing/input/PagedSeqReader.scala
+++ b/src/main/scala/scala/util/parsing/input/PagedSeqReader.scala
@@ -30,10 +30,10 @@ object PagedSeqReader {
  * @author Martin Odersky
  */
 class PagedSeqReader(seq: PagedSeq[Char],
-                     override val offset: Int) extends Reader[Char] {
+                     override val offset: Int) extends Reader[Char] { outer =>
   import PagedSeqReader._
 
-  override lazy val source: java.lang.CharSequence = seq
+  override val source: java.lang.CharSequence = seq
 
   /** Construct a `PagedSeqReader` with its first element at
    *  `source(0)` and position `(1,1)`.
@@ -51,7 +51,9 @@ class PagedSeqReader(seq: PagedSeq[Char],
    *         otherwise, it's a `PagedSeqReader` containing the rest of input.
    */
   def rest: PagedSeqReader =
-    if (seq.isDefinedAt(offset)) new PagedSeqReader(seq, offset + 1)
+    if (seq.isDefinedAt(offset)) new PagedSeqReader(seq, offset + 1) {
+      override val source: java.lang.CharSequence = outer.source
+    }
     else this
 
   /** The position of the first element in the reader.
@@ -67,5 +69,7 @@ class PagedSeqReader(seq: PagedSeq[Char],
    *  `n` elements.
    */
   override def drop(n: Int): PagedSeqReader =
-    new PagedSeqReader(seq, offset + n)
+    new PagedSeqReader(seq, offset + n) {
+      override val source: java.lang.CharSequence = outer.source
+    }
 }

From 0345e49849da4fa33df8c87d20f6920b0f1df0f0 Mon Sep 17 00:00:00 2001
From: Tomas Janousek <tomi@nomi.cz>
Date: Sat, 8 Aug 2015 11:54:18 +0200
Subject: [PATCH 2/2] Add test for #45

---
 .../scala/util/parsing/combinator/gh45.scala  | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 src/test/scala/scala/util/parsing/combinator/gh45.scala

diff --git a/src/test/scala/scala/util/parsing/combinator/gh45.scala b/src/test/scala/scala/util/parsing/combinator/gh45.scala
new file mode 100644
index 00000000..e184719a
--- /dev/null
+++ b/src/test/scala/scala/util/parsing/combinator/gh45.scala
@@ -0,0 +1,46 @@
+package scala.util.parsing.combinator
+
+import scala.util.parsing.input._
+import scala.collection.immutable.PagedSeq
+
+import org.junit.Test
+import org.junit.Assert.assertTrue
+
+import scala.util.parsing.combinator.syntactical.StandardTokenParsers
+
+class gh45 {
+
+  @Test
+  def test4: Unit = {
+    def check(rd: Reader[Char]): Unit = {
+      val g = new grammar
+      val p = g.phrase(g.script)
+      val parseResult = p(new g.lexical.Scanner(rd))
+      assertTrue(parseResult.isInstanceOf[g.Success[_]])
+    }
+
+    val str = "x once y"
+    check(new CharSequenceReader(str))
+    /* Note that this only tests PagedSeq.rest since neither
+     * PackratReader nor lexical.Scanner override/use the drop method.
+     */
+    check(new PagedSeqReader(PagedSeq.fromStrings(List(str))))
+  }
+
+}
+
+private final class grammar extends StandardTokenParsers with PackratParsers {
+  lexical.reserved ++= List("x", "y", "z", "once")
+
+  var onceCnt: Int = 0
+  lazy val once: PackratParser[String] = memo("once") ^? {
+    case s if onceCnt == 0 =>
+      onceCnt += 1
+      s
+  }
+
+  lazy val script: PackratParser[Any] =
+    ( "x" ~ once ~ "z"
+    | "x" ~ once ~ "y"
+    )
+}