Added --date, similar to --account and --payee

This lets you do things like store a date as the value of a tag, then
run:

  ledger --date='has_tag("Foo") ? to_date(tag("Foo")) : date' reg

src/chain.cc

@@ -159,6 +159,11 @@ post_handler_ptr chain_post_handlers(report_t&	      report,
     handler.reset(new sort_posts(handler, "date"));
   }
 
+  if (report.HANDLED(date_))
+    handler.reset(new transfer_details(handler, transfer_details::SET_DATE,
+				       report.session.journal->master,
+				       report.HANDLER(date_).str(),
+				       report));
   if (report.HANDLED(account_))
     handler.reset(new transfer_details(handler, transfer_details::SET_ACCOUNT,
 				       report.session.journal->master,

src/filters.cc

@@ -706,22 +706,27 @@ void transfer_details::operator()(post_t& post)
   temp.set_state(post.state());
 
   bind_scope_t bound_scope(scope, temp);
+  value_t      substitute(expr.calc(bound_scope));
 
   switch (which_element) {
-  case SET_PAYEE:
-    xact.payee = expr.calc(bound_scope).to_string();
+  case SET_DATE:
+    xact.set_date(substitute.to_date());
     break;
 
   case SET_ACCOUNT: {
     std::list<string> account_names;
     temp.account->remove_post(&temp);
-    split_string(expr.calc(bound_scope).to_string(), ':', account_names);
+    split_string(substitute.to_string(), ':', account_names);
     temp.account = create_temp_account_from_path(account_names, temps,
 						 xact.journal->master);
     temp.account->add_post(&temp);
     break;
   }
 
+  case SET_PAYEE:
+    xact.payee = substitute.to_string();
+    break;
+
   default:
     assert(false);
     break;

src/filters.h

@@ -550,8 +550,9 @@ class transfer_details : public item_handler<post_t>
 
 public:
   enum element_t {
-    SET_PAYEE,
-    SET_ACCOUNT
+    SET_DATE,
+    SET_ACCOUNT,
+    SET_PAYEE
   } which_element;
 
   transfer_details(post_handler_ptr handler,

src/item.h

@@ -172,6 +172,12 @@ public:
   virtual optional<date_t> effective_date() const {
     return _date_eff;
   }
+  virtual void set_date(const date_t& date) {
+    if (use_effective_date)
+      _date_eff = date;
+    else
+      _date = date;
+  }
 
   void set_state(state_t new_state) {
     _state = new_state;

src/report.cc

@@ -561,6 +561,7 @@ option_t<report_t> * report_t::lookup_option(const char * p)
     break;
   case 'd':
     OPT(daily);
+    else OPT(date_);
     else OPT(date_format_);
     else OPT(datetime_format_);
     else OPT(depth_);

src/report.h

@@ -217,6 +217,7 @@ public:
     HANDLER(csv_format_).report(out);
     HANDLER(current).report(out);
     HANDLER(daily).report(out);
+    HANDLER(date_).report(out);
     HANDLER(date_format_).report(out);
     HANDLER(datetime_format_).report(out);
     HANDLER(depth_).report(out);
@@ -450,6 +451,7 @@ public:
       parent->HANDLER(period_).on(string("--daily"), "daily");
     });
 
+  OPTION(report_t, date_);
   OPTION(report_t, date_format_);
   OPTION(report_t, datetime_format_);
 

src/value.cc

@@ -1146,6 +1146,12 @@ void value_t::in_place_cast(type_t cast_type)
     case AMOUNT:
       set_amount(amount_t(as_string()));
       return;
+    case DATE:
+      set_date(parse_date(as_string()));
+      return;
+    case DATETIME:
+      set_datetime(parse_datetime(as_string()));
+      return;
     case MASK:
       set_mask(as_string());
       return;