g++-5 abandons the non-standard CoW semantics for std::string, instead using interning for short strings. As a result, code like this no longer works:

    std::string file::get_pan_home() {...}
    const char * ph = file::get_pan_home().c_str();

because that c_str() returns start of buffer of a temporary std::string which is deleted at the semicolon - and ph is now pointing into the neverland.

Of course, that sort of code had never worked with other c++ compilers.

In general, returning std::string objects is bad practice - both because of unnecessary memory copying and heap fragmentation, and because it's tempting to call methods on those objects when they are still ephemeral, leading to crashes and bugs.

The end result of all this is some of pan's files like newrsc-1 etc. are being created in the current working directory instead of ~/.pan - since with g++-5, file::absolute_fn() in git master and newsrc_fn() in 0.139 tarball release are broken. This was reported to us downstream at https://bugs.gentoo.org/show_bug.cgi?id=559666

The attached patch fixes file::get_pan_home() by returning const string reference to the static function-local object instead of a new string object.

My suggestion is to carefully go through the entire project codebase - there are lots of functions returning std::string, and I suspect that not all of their callers are compatible with the standard, non-g++-4 string semantics.