CI is not checking compatibility with MacOs clang

[huitema]

@larseggert just found a bug in a recent PR because the new code introduced a variable named "xor". This works fine with many compilers (gcc, mscc) but clang throws an error because it treats "xor" as a keyword.

What is really weird is that the offending code passed the integration checks, including this run, which tests with:

    - name: Linux (clang)
      os: linux
      compiler: clang

The issue is being fixed in PR #332, but we should also fix the integration test that did not discover the problem.

[larseggert]

FWIW, I am using clang-11 installed via homebrew, not the Apple clang

[huitema]

@larseggert do you have a suggestion on how to modify the yml and catch such issues in the future?

[huitema]

Also, what clang is doing here is importing in the C compiler tokens that are only defined in C++. The Clang 11 token binding source file includes:

// C++ 2.5p2: Alternative Representations.
CXX_KEYWORD_OPERATOR(and     , ampamp)
CXX_KEYWORD_OPERATOR(and_eq  , ampequal)
CXX_KEYWORD_OPERATOR(bitand  , amp)
CXX_KEYWORD_OPERATOR(bitor   , pipe)
CXX_KEYWORD_OPERATOR(compl   , tilde)
CXX_KEYWORD_OPERATOR(not     , exclaim)
CXX_KEYWORD_OPERATOR(not_eq  , exclaimequal)
CXX_KEYWORD_OPERATOR(or      , pipepipe)
CXX_KEYWORD_OPERATOR(or_eq   , pipeequal)
CXX_KEYWORD_OPERATOR(xor     , caret)
CXX_KEYWORD_OPERATOR(xor_eq  , caretequal)

Was the bug found in a C compile, or was the code imported in C++?

[larseggert]

C++

[huitema]

I think that's the issue, C++. Picotls is purely C, so the tests won't catch conflicts with C++ keywords. I had a similar problem in Picoquic, and solved it by adding an explicit C++ test. Something as simple as compiling hello word in C++ while including picotls.h might suffice.

[huitema]

By the way, Clang11 should know better. The header includes

#ifdef __cplusplus
extern "C" {
#endif

A standard conformant compiler should know that what follows is C code, not C++ code...

[huitema]

Here is the C++ code that I use in picoquic:

/* Simple test using C++.
 * The goal is to verify that the libraries are accessible from C++, and that compilation works.
 */
#ifdef _WINDOWS
#include "wincompat.h"
#endif
#include "picoquic.h"
#include "picohash.h"
#include "picoquic_internal.h"
#include "picoquic_utils.h"
#include "picosocks.h"
#include "picoquictest.h"
#include "picoquictest_internal.h"

extern "C" {
    int cplusplustest() {
        return 0;
    }
}

Replace picoquic headers by picotls headers, add that to the test library, and call cplusplustest from the test suite. Maybe add one of these for each of minicrypto, openssl and fusion. @kazuho, what do you think?

[kazuho]

@huitema Thank you for the suggestion. I'll add something like that to our tests.

A standard conformant compiler should know that what follows is C code, not C++ code...

FWIW extern "C" changes the linkage (i.e. name mangling rule), but does not change how the source code is being interpreted. Therefore, clang is correct to complain about the header files using a C++ keyword (sigh).