wallet: Add macro to annotate SQL statements

These two simple macros have a twofold use:

 1) They serve as annotations for the query extraction tool to find them when
 extracting queries from the C source code.
 2) They replace the actual queries with names that can be used to lookup the
 queries in a table again, once they have been rewritten into the target SQL dialect.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

wallet/db.h

@@ -25,6 +25,28 @@ struct db {
 	const char **changes;
 };
 
+/**
+ * Macro to annotate a named SQL query.
+ *
+ * This macro is used to annotate SQL queries that might need rewriting for
+ * different SQL dialects. It is used both as a marker for the query
+ * extraction logic in devtools/sql-rewrite.py to identify queries, as well as
+ * a way to swap out the query text with it's name so that the query execution
+ * engine can then look up the rewritten query using its name.
+ *
+ */
+#define NAMED_SQL(name,x) x
+
+/**
+ * Simple annotation macro that auto-generates names for NAMED_SQL
+ *
+ * If this macro is changed it is likely that the extraction logic in
+ * devtools/sql-rewrite.py needs to change as well, since they need to
+ * generate identical names to work correctly.
+ */
+#define SQL(x) NAMED_SQL( __FILE__ ":" stringify(__LINE__) ":" stringify(__COUNTER__), x)
+
+
 /**
  * db_setup - Open a the lightningd database and update the schema
  *