Bug 797133 - CSV Import of multicurrency transaction export in multiline form

The csv parser was using xaccParseAmount to convert price strings into GncNumerics.
However our export code can generate prices in rational form which xaccParseAmount
can't convert. So for prices the csv parser now uses the expression parser instead
to convert the string into a GncNumeric.

gnucash/import-export/csv-imp/gnc-imp-props-tx.cpp

@@ -35,6 +35,7 @@ extern "C" {
 #include "Account.h"
 #include "Transaction.h"
 #include "gnc-pricedb.h"
+#include <gnc-exp-parser.h>
 
 }
 
@@ -193,6 +194,32 @@ gnc_commodity* parse_commodity (const std::string& comm_str)
         return comm;
 }
 
+
+static GncNumeric parse_price (const std::string &str)
+{
+    /* An empty field is treated as zero */
+    if (str.empty())
+        return GncNumeric{};
+
+    /* Strings otherwise containing not digits will be considered invalid */
+    if(!boost::regex_search(str, boost::regex("[0-9]")))
+        throw std::invalid_argument (_("Value doesn't appear to contain a valid number."));
+
+    auto expr = boost::make_u32regex("[[:Sc:]]");
+    std::string str_no_symbols = boost::u32regex_replace(str, expr, "");
+
+    /* Convert based on user chosen currency format */
+    gnc_numeric val = gnc_numeric_zero();
+    char *endptr;
+
+    auto success = gnc_exp_parser_parse (str.c_str(), &val, &endptr);
+    gnc_exp_parser_shutdown();
+    if (!success)
+        throw std::invalid_argument (_("Price can't be parsed into a number."));
+
+    return GncNumeric(val);
+}
+
 void GncPreTrans::set (GncTransPropType prop_type, const std::string& value)
 {
     try
@@ -437,7 +464,7 @@ void GncPreSplit::set (GncTransPropType prop_type, const std::string& value)
 
             case GncTransPropType::PRICE:
                 m_price = boost::none;
-                m_price = parse_amount (value, m_currency_format); // Will throw if parsing fails
+                m_price = parse_price (value); // Will throw if parsing fails
                 break;
 
             case GncTransPropType::REC_STATE: