adds the lookahead routine to the parser

Introduces a scoping operator used to temporarily look into the future.
Backs up scanner data before evaluating a block and restores it after.

Not used anywhere, only necessary for the upcoming quasiquote patch
in order to reliably detect and accordingly process holes in quasiquoted
Scala syntax.

1 files changed, 23 insertions, 10 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala b/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
index 2dca39f7a3..03cdead472 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Scanners.scala
@@ -5,7 +5,7 @@
 package scala.tools.nsc
 package ast.parser
 
-import scala.tools.nsc.util.CharArrayReader
+import scala.tools.nsc.util.{ CharArrayReader, CharArrayReaderData }
 import scala.reflect.internal.util._
 import scala.reflect.internal.Chars._
 import Tokens._
@@ -71,17 +71,37 @@ trait Scanners extends ScannersCommon {
     /** the base of a number */
     var base: Int = 0
 
-    def copyFrom(td: TokenData) = {
+    def copyFrom(td: TokenData): this.type = {
       this.token = td.token
       this.offset = td.offset
       this.lastOffset = td.lastOffset
       this.name = td.name
       this.strVal = td.strVal
       this.base = td.base
+      this
     }
   }
 
-  abstract class Scanner extends CharArrayReader with TokenData with ScannerCommon {
+  /** An interface to most of mutable data in Scanner defined in TokenData
+   *  and CharArrayReader (+ next, prev fields) with copyFrom functionality
+   *  to backup/restore data (used by quasiquotes' lookingAhead).
+   */
+  trait ScannerData extends TokenData with CharArrayReaderData {
+    /** we need one token lookahead and one token history
+     */
+    val next: TokenData = new TokenData{}
+    val prev: TokenData = new TokenData{}
+
+    def copyFrom(sd: ScannerData): this.type = {
+      this.next copyFrom sd.next
+      this.prev copyFrom sd.prev
+      super[CharArrayReaderData].copyFrom(sd)
+      super[TokenData].copyFrom(sd)
+      this
+    }
+  }
+
+  abstract class Scanner extends CharArrayReader with TokenData with ScannerData with ScannerCommon {
     private def isDigit(c: Char) = java.lang.Character isDigit c
 
     private var openComments = 0
@@ -194,13 +214,6 @@ trait Scanners extends ScannersCommon {
       cbuf.clear()
     }
 
-    private class TokenData0 extends TokenData
-
-    /** we need one token lookahead and one token history
-     */
-    val next : TokenData = new TokenData0
-    val prev : TokenData = new TokenData0
-
     /** a stack of tokens which indicates whether line-ends can be statement separators
      *  also used for keeping track of nesting levels.
      *  We keep track of the closing symbol of a region. This can be