+/**
+ * @file match_bug.cpp
+ *
+ * Check for bug in GiNaC::ex::match() described here:
+ * http://www.ginac.de/pipermail/ginac-devel/2006-April/000942.html
+ */
+#include "ginac.h"
+#include "error_report.hpp"
+#include <iostream>
+using namespace GiNaC;
+
+/*
+ * basic::match(lst&) used to have an obscure side effect: repl_lst
+ * could be modified even if the match failed! Although this "feature"
+ * was documented it happend to be very confusing *even for GiNaC
+ * developers*, see
+ * http://www.ginac.de/pipermail/ginac-devel/2006-April/000942.html
+ *
+ * It was fixed in 192ed7390b7b2b705ad100e3db0a92eedd2b20ad. Let's make
+ * sure it will be never re-added:
+ */
+static void failed_match_have_side_effects()
+{
+ symbol x("x");
+ ex e = pow(x, 5);
+ ex pattern = pow(wild(0), -1);
+ // obviously e does NOT match the pattern
+ lst repl_lst;
+ bool match_p = e.match(pattern, repl_lst);
+ bug_on(match_p, "match(" << e << ", " << pattern << ") says \"Yes\"");
+ bug_on(repl_lst.nops() != 0,
+ "failed match have side effects: repl_lst = " << repl_lst);
+}
+
+/*
+ * As a consequence of the bug described above pattern matching can wrongly
+ * fail. In particular, x^5*y^(-1) fails to match ($0)^(-1)*x^($2).
+ *
+ * The first thing that is attempted to match is x^5 with $0^(-1). This match
+ * will fail. However repl_lst will contain $0 == x as a side effect. This
+ * repl_lst will prevent the match of y^(-1) to ($0)^(-1) to succeed.
+ *
+ * This issue was worked around by 73f0ce4cf8d91f073f35a45443f5fbe886921c5c.
+ * Now we have a real fix (192ed7390b7b2b705ad100e3db0a92eedd2b20ad), but
+ * let's add a check.
+ */
+static void match_false_negative()
+{
+ symbol x("x"), y("y");
+ ex e = pow(x, 5)*pow(y, -1);
+ ex pattern = pow(wild(0), -1)*pow(x, wild(2));
+ lst repl_lst;
+ bool match_p = e.match(pattern, repl_lst);
+ bug_on(!match_p, "false negative: " << e << " did not match "
+ << pattern);
+}
+
+int main(int argc, char** argv)
+{
+ std::cout << "checking for historical bugs in match()... " << std::flush;
+ failed_match_have_side_effects();
+ match_false_negative();
+ std::cout << "not found. ";
+ return 0;
+}
+