This experimental branch attempts to use columns for an index-on-expression

in place of the expression that is being indexed.  This particular check-in
mostly works, but there are still issues.

FossilOrigin-Name: 2e8d4fd4cfd9e82f33c707ba246fe2bb3ca01762cf5ac5905058fbc7adf0abe7

src/insert.c

@@ -96,6 +96,7 @@ const char *sqlite3IndexAffinityStr(sqlite3 *db, Index *pIdx){
         aff = SQLITE_AFF_INTEGER;
       }else{
         assert( x==XN_EXPR );
+        assert( pIdx->bHasExpr );
         assert( pIdx->aColExpr!=0 );
         aff = sqlite3ExprAffinity(pIdx->aColExpr->a[n].pExpr);
       }