From d7370772a48b1bee07473c8ba080306c18e60933 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 3 Oct 2013 08:11:17 +0200
Subject: Add support for compile-time detection of unnecessary data migration
 functions

---
 odb/details/meta/static-assert.hxx | 33 +++++++++++++++++++
 odb/schema-catalog.hxx             | 66 +++++++++++++++++++++++++++++++++-----
 2 files changed, 91 insertions(+), 8 deletions(-)
 create mode 100644 odb/details/meta/static-assert.hxx

diff --git a/odb/details/meta/static-assert.hxx b/odb/details/meta/static-assert.hxx
new file mode 100644
index 0000000..6bb84f2
--- /dev/null
+++ b/odb/details/meta/static-assert.hxx
@@ -0,0 +1,33 @@
+// file      : odb/details/meta/static-assert.hxx
+// copyright : Copyright (c) 2009-2013 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+#ifndef ODB_DETAILS_META_STATIC_ASSERT_HXX
+#define ODB_DETAILS_META_STATIC_ASSERT_HXX
+
+#include <odb/pre.hxx>
+
+#include <odb/details/config.hxx> // ODB_CXX11
+
+#ifndef ODB_CXX11
+
+namespace odb
+{
+  namespace details
+  {
+    namespace meta
+    {
+      template <bool>
+      struct static_assert_test;
+
+      template <>
+      struct static_assert_test<true> {};
+    }
+  }
+}
+
+#endif
+
+#include <odb/post.hxx>
+
+#endif // ODB_DETAILS_META_STATIC_ASSERT_HXX
diff --git a/odb/schema-catalog.hxx b/odb/schema-catalog.hxx
index c02de4a..968cbdc 100644
--- a/odb/schema-catalog.hxx
+++ b/odb/schema-catalog.hxx
@@ -19,6 +19,8 @@
 #include <odb/forward.hxx> // schema_version, odb::core
 
 #include <odb/details/export.hxx>
+#include <odb/details/unused.hxx>
+#include <odb/details/meta/static-assert.hxx>
 
 namespace odb
 {
@@ -77,8 +79,60 @@ namespace odb
     typedef void (*data_migration_function_type) (database&);
 #endif
 
+    // The following three variants of the registration functions make
+    // sure that the version is greater that the base model version.
+    // This helps with identifying and removing data migration function
+    // that are no longer required.
+    //
     // Data migration functions are called in the order of registration.
     //
+    template <schema_version v, schema_version base>
+    static void
+    data_migration_function (data_migration_function_type f,
+                             const std::string& name = "")
+    {
+      data_migration_function<v, base> (id_common, f, name);
+    }
+
+    // Database-specific data migration.
+    //
+    template <schema_version v, schema_version base>
+    static void
+    data_migration_function (database& db,
+                             data_migration_function_type f,
+                             const std::string& name = "")
+    {
+      data_migration_function<v, base> (db.id (), f, name);
+    }
+
+    template <schema_version v, schema_version base>
+    static void
+    data_migration_function (database_id id,
+                             data_migration_function_type f,
+                             const std::string& name = "")
+    {
+      // If the data migration version is below the base model version
+      // then it will never be called.
+      //
+#ifdef ODB_CXX11
+      static_assert (v > base || base == 0,
+                     "data migration function is no longer necessary");
+#else
+      // Poor man's static_assert.
+      //
+      typedef details::meta::static_assert_test<(v > base || base == 0)>
+      data_migration_function_is_no_longer_necessary;
+
+      char sa [sizeof (data_migration_function_is_no_longer_necessary)];
+      ODB_POTENTIALLY_UNUSED (sa);
+#endif
+
+      data_migration_function (id, v, f, name);
+    }
+
+    // The same as above but take the version as an argument and do
+    // not check whether it is greater than the base model version.
+    //
     static void
     data_migration_function (schema_version v,
                              data_migration_function_type f,
@@ -87,8 +141,6 @@ namespace odb
       data_migration_function (id_common, v, f, name);
     }
 
-    // Database-specific data migration.
-    //
     static void
     data_migration_function (database& db,
                              schema_version v,
@@ -175,23 +227,21 @@ namespace odb
 
   // Static data migration function registration.
   //
+  template <schema_version v, schema_version base>
   struct LIBODB_EXPORT data_migration_entry
   {
     typedef schema_catalog::data_migration_function_type function_type;
 
-    data_migration_entry (schema_version v,
-                          function_type f,
-                          const std::string& name = "")
+    data_migration_entry (function_type f, const std::string& name = "")
     {
-      schema_catalog::data_migration_function (v, f, name);
+      schema_catalog::data_migration_function<v, base> (f, name);
     }
 
     data_migration_entry (database_id id,
-                          schema_version v,
                           function_type f,
                           const std::string& name = "")
     {
-      schema_catalog::data_migration_function (id, v, f, name);
+      schema_catalog::data_migration_function<v, base> (id, v, f, name);
     }
   };
 
-- 
cgit v1.1