Avoid infinite loop when unarchiving realsymbol and possymbol.

symbol::read_archive(): explicitly set status_flags::evaluated (and
status_flags::expanded) on object being unarchived. These flags get
reset by basic::operator=(const basic&) for realsymbol and possymbol,
and nothing sets (except symbol ctor), so automatic evaluation never
terminates (or rather, terminates due to a stack overflow). Therefore
it's necessary need to set status_flags::evaluated explicitly.

Thanks to Markus Fröb for a bugreport and a test case.
(cherry picked from commit e99d0d58c1bbaa8ee73e4a90a90aa1086f2f813d)

diff --git a/ginac/symbol.cpp b/ginac/symbol.cpp
index 9897bb4c3b5de35d2344ae90d13bd08d134d247b..c9db110fdc43a1cfb581128d48f592553644cfae 100644 (file)
--- a/ginac/symbol.cpp
+++ b/ginac/symbol.cpp
@@ -109,6 +109,15 @@ void symbol::read_archive(const archive_node &n, lst &sym_lst)
        for (lst::const_iterator it = sym_lst.begin(); it != sym_lst.end(); ++it) {
                if (is_a<symbol>(*it) && (ex_to<symbol>(*it).name == tmp_name)) {
                        *this = ex_to<symbol>(*it);
+                       // XXX: This method is responsible for reading realsymbol
+                       // and possymbol objects too. But
+                       // basic::operator=(const basic& other)
+                       // resets status_flags::evaluated if other and *this are
+                       // of different types. Usually this is a good idea, but
+                       // doing this for symbols is wrong (for one, nothing is
+                       // going to set status_flags::evaluated, evaluation will
+                       // loop forever). Therefore we need to restore flags.
+                       setflag(status_flags::evaluated | status_flags::expanded);
                        return;
                }
        }