[llvm-bugs] [Bug 43352] New: Undefined symbols when using boost statecharts

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43352

            Bug ID: 43352
           Summary: Undefined symbols when using boost statecharts
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: COFF
          Assignee: unassignedbugs at nondot.org
          Reporter: brian.j.cody at gmail.com
                CC: llvm-bugs at lists.llvm.org

Version 9.0.0 RC5

The same link works in ld. You can use the boost statechart as such:

namespace my_namespace
{
struct evt_done_state: boost::statechart::event<evt_done_state> {};
}

lld-link: error: undefined symbol:
__ZN5boost10statechart6detail10no_contextIN12my_namespace14evt_done_stateEE11no_funct>>>
referenced by (... file path)


Looking at the boost source code, there is declared, undefined function. This
was taken from boost 1.63.0, but the specific code is common for older and
newer versions:
boost\statechart\detail\reaction_dispatcher.hpp:33
template< class Event >
struct no_context
{
  void no_function( const Event & ); // <------
};

The method is not called or referenced, and shows up as 'U' in nm. I suspect ld
drops the unused, undefined symbol.

We're working around this by changing the offending line to:
void no_function( const Event & ) {}

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