Early detection of database corruption in balance_deeper().

FossilOrigin-Name: 61c2233654158e65a3d3baeea947903a919a569fcc4a5b342b2e9a68cec1b6f3

src/sqliteInt.h

@@ -446,6 +446,26 @@
 # define NEVER(X)       (X)
 #endif
 
+/*
+** The harmless(X) macro indicates that expression X is usually false
+** but can be true without causing any problems, but we don't know of
+** any way to cause X to be true.
+**
+** In debugging and testing builds, this macro will abort if X is ever
+** true.  In this way, developers are alerted to a possible test case
+** that causes X to be true.  If a harmless macro ever fails, that is
+** an opportunity to change the macro into a testcase() and add a new
+** test case to the test suite.
+**
+** For normal production builds, harmless(X) is a no-op, since it does
+** not matter whether expression X is true or false.
+*/
+#ifdef SQLITE_DEBUG
+# define harmless(X)  assert(!(X));
+#else
+# define harmless(X)
+#endif
+
 /*
 ** Some conditionals are optimizations only.  In other words, if the
 ** conditionals are replaced with a constant 1 (true) or 0 (false) then