Removal of line continuations doesn't insert line directive.

[realazthat]

When running wave on the following code:

/*
 Thing that goes here \
 Continuation inside a comment here \
 I dunno what is supposed to happen to the continuations, or if it is disallowed, but that's OKAY.
*/

int main() {
  return 0;
}

It gets preprocessed into the following:

/*
 Thing that goes here  Continuation inside a comment here  I dunno what is supposed to happen to the continuations, or if it is disallowed, but that's OKAY.
*/

int main() {
  return 0;
}

Note that the line continuations were removed, but no #line directive was emitted to fix the line numbers.

Note, ctx.set_language(/*language=*/enable_preserve_comments(ctx.get_language())); option was set, to preserve the comments.

Note, I have not tested if this problem occurs outside a comment, but a comment makes it more complicated, since the line directive would presumably need to be placed outside of the comment.

Minimum reproducible example:

#include <iostream>
#include <sstream>
#include <string>

#include "boost/wave.hpp"
#include "boost/wave/cpp_context.hpp"
#include "boost/wave/cpp_exceptions.hpp"
#include "boost/wave/cpplexer/cpp_lex_iterator.hpp"
#include "boost/wave/language_support.hpp"

int main() {
  using namespace boost::wave::context_policies;
  using namespace boost::wave;
  using ContextPolicy_ = default_preprocessing_hooks;
  using lex_iterator_type = cpplexer::lex_iterator<cpplexer::lex_token<>>;
  using context_type =
      context<std::string::const_iterator, lex_iterator_type,
              iteration_context_policies::load_file_to_string, ContextPolicy_>;

  const std::string shader_source = R"str(
/*
 Thing that goes here \
 Continuation inside a comment here \
 I dunno what is supposed to happen to the continuations, or if it is disallowed, but that's OKAY.
*/

int main() {
  return 0;
}
)str";
  std::string shader_path = "code.cc";

  context_type ctx(/*first_=*/shader_source.begin(),
                   /*last_=*/shader_source.end(),
                   /*fname=*/shader_path.c_str());
  ctx.set_language(
      /*language=*/enable_preserve_comments(ctx.get_language()));
  ctx.set_language(
      /*language=*/enable_emit_line_directives(ctx.get_language()));

  context_type::iterator_type first = ctx.begin();
  context_type::iterator_type last = ctx.end();

  std::ostringstream sstr;
  while (first != last) {
    sstr << (*first).get_value();
    ++first;
  }

  std::string preprocessed = sstr.str();
  std::cout << preprocessed;
  return 0;
}

[jefftrull]

FWIW the wave tool gets the right output here with -p 2

[jefftrull]

It looks like using eat_whitespace instead of default_preprocessor_hooks fixes the issue. I can no longer remember why these are different things or why one would produce line directives and the other not.

[jefftrull]

I think this is arguably "working as designed" so if you don't have a specific complaint I think we should close this.

[jefftrull]

Closing per above message, please reopen if you think we should pursue further.