Added nail_down() for pinning market value exprs

src/commodity.cc

@@ -217,6 +217,15 @@ commodity_t::check_for_updated_price(const optional<price_point_t>& point,
   return point;
 }
 
+commodity_t& commodity_t::nail_down(const expr_t& expr)
+{
+  annotation_t new_details;
+  new_details.value_expr = expr;
+  commodity_t * new_comm =
+    commodity_pool_t::current_pool->find_or_create(symbol(), new_details);
+  return *new_comm;
+}
+
 commodity_t::operator bool() const
 {
   return this != pool().null_commodity;

src/commodity.h

@@ -291,6 +291,8 @@ public:
                           const optional<datetime_t>&    moment,
                           const optional<commodity_t&>&  in_terms_of);
 
+  commodity_t& nail_down(const expr_t& expr);
+
   // Methods related to parsing, reading, writing, etc., the commodity
   // itself.
 

src/report.cc

@@ -736,6 +736,24 @@ value_t report_t::fn_commodity(call_scope_t& args)
   return string_value(args.get<amount_t>(0).commodity().symbol());
 }
 
+value_t report_t::fn_nail_down(call_scope_t& args)
+{
+  value_t arg0(args[0]);
+  switch (arg0.type()) {
+  case value_t::AMOUNT: {
+    amount_t tmp(arg0.as_amount());
+    if (tmp.has_commodity())
+      tmp.set_commodity(tmp.commodity()
+                        .nail_down(args[1].as_any<expr_t::ptr_op_t>()));
+    return tmp;
+  }
+
+  default:
+    throw_(std::runtime_error, _("Attempting to nail down %1")
+           << args[0].label());
+  }
+}
+
 value_t report_t::fn_lot_date(call_scope_t& args)
 {
   if (args[0].has_annotation()) {
@@ -1261,6 +1279,8 @@ expr_t::ptr_op_t report_t::lookup(const symbol_t::kind_t kind,
         return WRAP_FUNCTOR(fn_null);
       else if (is_eq(p, "now"))
         return MAKE_FUNCTOR(report_t::fn_now);
+      else if (is_eq(p, "nail_down"))
+        return MAKE_FUNCTOR(report_t::fn_nail_down);
       break;
 
     case 'o':

src/report.h

@@ -170,6 +170,7 @@ public:
   value_t fn_ansify_if(call_scope_t& scope);
   value_t fn_percent(call_scope_t& scope);
   value_t fn_commodity(call_scope_t& scope);
+  value_t fn_nail_down(call_scope_t& scope);
   value_t fn_lot_date(call_scope_t& scope);
   value_t fn_lot_price(call_scope_t& scope);
   value_t fn_lot_tag(call_scope_t& scope);