Add function to create an absolute file path

Add function to create an absolute file path from a prefix path and a
relative one. If the prefix is null, then the root directory of the
current path is used.

libgnucash/core-utils/gnc-filepath-utils.cpp

@@ -728,6 +728,7 @@ static std::string migrate_gnc_datahome()
 }
 
 
+
 #if defined G_OS_WIN32 ||defined MAC_INTEGRATION
 constexpr auto path_package = PACKAGE_NAME;
 #else
@@ -1017,6 +1018,35 @@ gnc_userdata_dir_as_path (void)
     return gnc_userdata_home;
 }
 
+gchar *gnc_file_path_absolute (const gchar *prefix, const gchar *relative)
+{
+    bfs::path path_relative (relative);
+    path_relative.imbue (bfs_locale);
+    bfs::path path_absolute;
+    bfs::path path_head;
+
+    if (prefix == nullptr)
+    {
+        const gchar *doc_dir = g_get_user_special_dir (G_USER_DIRECTORY_DOCUMENTS);
+        if (doc_dir == nullptr)
+            path_head = bfs::path (gnc_userdata_dir ()); // running as root maybe
+        else
+            path_head = bfs::path (doc_dir);
+
+        path_head.imbue (bfs_locale);
+        path_absolute = absolute (path_relative, path_head);
+    }
+    else
+    {
+        bfs::path path_head (prefix);
+        path_head.imbue (bfs_locale);
+        path_absolute = absolute (path_relative, path_head);
+    }
+    path_absolute.imbue (bfs_locale);
+
+    return g_strdup (path_absolute.string().c_str());
+}
+
 /** @fn gchar * gnc_build_userdata_path (const gchar *filename)
  *  @brief Make a path to filename in the user's configuration directory.
  *

libgnucash/core-utils/gnc-filepath-utils.h

@@ -49,6 +49,15 @@ gchar *gnc_resolve_file_path (const gchar *filefrag);
  */
 gchar *gnc_file_path_relative_part (const gchar *prefix, const gchar *path);
 
+/** Given a prefix and a relative path, return the absolute path.
+ * @param prefix The prefix that is the head of the path
+ * @param relative The path to add to the prefix to form an absolute path
+ * @return a char* that must be g_freed containing the absolute path.
+ *
+ * If prefix is null, then the gnc_userdata_home is used as the prefix.
+ */
+gchar *gnc_file_path_absolute (const gchar *prefix, const gchar *relative);
+
 /** @brief Find an absolute path to a localized version of a given
  *  relative path to a html or html related file.
  *  If no localized version exists, an absolute path to the file