* Revert r19650 (implement gc-keep-outputs by looking for derivations

with the same name as the output) and instead use the
  DerivationOutputs table in the database, which is the correct way to
  to do things.

src/libstore/local-store.hh

@@ -103,6 +103,12 @@ public:
     void queryReferrers(const Path & path, PathSet & referrers);
 
     Path queryDeriver(const Path & path);
+
+    /* Return all currently valid derivations that have `path' as an
+       output.  (Note that the result of `queryDeriver()' is the
+       derivation that was actually used to produce `path', which may
+       not exist anymore.) */
+    PathSet queryValidDerivers(const Path & path);
     
     PathSet querySubstitutablePaths();
     
@@ -199,6 +205,7 @@ private:
     SQLiteStmt stmtRegisterFailedPath;
     SQLiteStmt stmtHasPathFailed;
     SQLiteStmt stmtAddDerivationOutput;
+    SQLiteStmt stmtQueryValidDerivers;
 
     int getSchema();
 
@@ -228,8 +235,6 @@ private:
 
     bool tryToDelete(GCState & state, const Path & path);
     
-    PathSet findDerivers(GCState & state, const Path & path);
-    
     bool isActiveTempFile(const GCState & state,
         const Path & path, const string & suffix);