archive: rename ParseSink to NARParseVisitor

- Rename the listener to not be called a "sink". If it were a "sink" it
  would be eating bytes and conform with any of the Nix sink stuff
  (maybe FileHandle should be a Sink itself! but that's a later CL's
  problem). This is a parser listener.
- Move the RetrieveRegularNARSink thing into store-api.cc, which is its
  only usage, and fix it to actually do what it is stated to do: crash
  if its invariants are violated.

  It's, of course, used to erm, unpack single-file NAR files, generated
  via a horrible contraption of sources and sinks that looks like a
  plumbing blueprint. Refactoring that is a future task.
- Add a description of the invariants of NARParseVisitor in preparation
  of refactoring it.

Change-Id: Ifca1d74d2947204a1f66349772e54dad0743e944

1 files changed, 2 insertions, 1 deletions

diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index f0dfcb19b..fa7d5e3cb 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -2,6 +2,7 @@
 #include "archive.hh"
 
 #include <map>
+#include <memory>
 #include <stack>
 #include <algorithm>
 
@@ -33,7 +34,7 @@ struct NarAccessor : public FSAccessor
 
     NarMember root;
 
-    struct NarIndexer : ParseSink, Source
+    struct NarIndexer : NARParseVisitor, Source
     {
         NarAccessor & acc;
         Source & source;