Changes to SWI-cpp.h API

[kamahen]

This PR requires SWI-Prolog/packages-cpp#16 and should be committed as soon as possible after a new release contains the SWI-cpp.h changes (probably 8.5.16).

[mgondan]

Thank you. I'll check it when 8.5.16 is out.

[kamahen]

I presume that the "checks were not successful" was because it uses the current swipl, which doesn't have the updated SWI-cpp.h; and that the checks will succeed whenever a new version of swipl is released.

[mgondan]

Exactly. Let's wait until the new header files are available.

[kamahen]

The code in SWI-cpp2.h appears to have a bug, which I haven't had time to fix. This doesn't seem to affect any of the systems that I know of that use SWI-cpp2.h (rolog, rocksdb, swipl-win). When I fix the bug (hopefully within a week), I will send you a message, so that you can do whatever testing you need with the updated code.

My apologies -- I was sick (not COVID) and the work on the new C++ API isn't quite finished.

[mgondan]

Thanks, Peter. I am currently testing it, so far, I didn’t encounter any problems.

[kamahen]

The PlCall() bug seems to be an incompatibility with ASAN; I've run my tests with Debug turned on, and they all pass, so far. I have a few small changes that I'm trying to get finished in time for the v9 release.
If you've made changes to the rolog code, please push them to github, or send me a patch/diff - so that I can run your tests with my latest version of SWI-cpp2.h

[mgondan]

Thanks, Peter. The github version is the most recent one.

[kamahen]

I have built rolog with the latest version from github but haven't run any tests.
The latest (and I hope final) version of SWI-cpp2.h is in SWI-Prolog/packages-cpp#25
These didn't cause any code changes to rolog, so probably they won't break any of your tests (the changes were mainly for rocksdb, which uses a lot more of the C++ API).

[kamahen]

The latest release of SWI-cpp2.h (just released with SWI-Prolog 9.x) has some additional [[nodiscard]] declarations, which cause warning messages in rolog if compiled with -Wunused-result.

You can fix these by simply wrapping the call with PlCheck. For example, line 270:

    tail.next(v) ;

becomes

    PlCheck(tail.next(v));

etc.

These are the warnings that I saw with my copy of rolog:

rolog.cpp:270:14: warning: ignoring return value of ‘bool PlTerm_tail::next(PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  270 |     tail.next(v) ;
      |     ~~~~~~~~~^~~
rolog.cpp: In function ‘PlTerm r2pl_null()’:
rolog.cpp:432:24: warning: ignoring return value of ‘bool PlTerm_tail::close()’, declared with attribute ‘nodiscard’ [-Wunused-result]
  432 |   PlTerm_tail(pl).close() ;
      |   ~~~~~~~~~~~~~~~~~~~~~^~
rolog.cpp: In function ‘PlTerm r2pl_var(Rcpp::ExpressionVector, Rcpp::CharacterVector&, PlTerm&, Rcpp::List)’:
rolog.cpp:564:14: warning: ignoring return value of ‘bool PlTerm_tail::next(PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  564 |     tail.next(v) ;
      |     ~~~~~~~~~^~~
rolog.cpp:572:14: warning: ignoring return value of ‘bool PlTerm_tail::append(const PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  572 |   tail.append(pl) ;
      |   ~~~~~~~~~~~^~~~
rolog.cpp: In function ‘PlTerm r2pl_list(Rcpp::List, Rcpp::CharacterVector&, PlTerm&, Rcpp::List)’:
rolog.cpp:672:18: warning: ignoring return value of ‘bool PlTerm_tail::append(const PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  672 |       tail.append(PlCompound("-", PlTermv(PlTerm_atom(n(i)), arg))) ;
      |       ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rolog.cpp:674:18: warning: ignoring return value of ‘bool PlTerm_tail::append(const PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  674 |       tail.append(arg) ; // no name
      |       ~~~~~~~~~~~^~~~~
rolog.cpp:677:13: warning: ignoring return value of ‘bool PlTerm_tail::close()’, declared with attribute ‘nodiscard’ [-Wunused-result]
  677 |   tail.close() ;
      |   ~~~~~~~~~~^~
rolog.cpp: In member function ‘Rcpp::List RlQuery::bindings()’:
rolog.cpp:808:14: warning: ignoring return value of ‘bool PlTerm_tail::next(PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  808 |     tail.next(v) ;
      |     ~~~~~~~~~^~~
rolog.cpp: In function ‘Rcpp::RObject portray_(Rcpp::RObject, Rcpp::List)’:
rolog.cpp:931:14: warning: ignoring return value of ‘bool PlTerm_tail::append(const PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  931 |   tail.append(PlCompound("quoted", PlTermv(PlTerm_atom("false")))) ;
      |   ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rolog.cpp:932:14: warning: ignoring return value of ‘bool PlTerm_tail::append(const PlTerm&)’, declared with attribute ‘nodiscard’ [-Wunused-result]
  932 |   tail.append(PlCompound("spacing", PlTermv(PlTerm_atom("next_argument")))) ;
      |   ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rolog.cpp:933:13: warning: ignoring return value of ‘bool PlTerm_tail::close()’, declared with attribute ‘nodiscard’ [-Wunused-result]
  933 |   tail.close() ;
      |   ~~~~~~~~~~^~

[kamahen]

These warnings are removed in PR #3