[libc++][CI] Fixes robust against ADL for C++03.

[Mordante]

Summary

This was disabled in D139545.

[philnik]

Where does this fire? noexcept(cond) should never be used in C++03.

[Mordante]

In D140731#4020155, @philnik wrote:

Where does this fire? noexcept(cond) should never be used in C++03.

include/__functional/invoke.h lines 431 and 438 are the only two places

template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, false, _Ret, _Fp, _Args...>
{
    typedef __nothrow_invokable_r_imp _ThisT;
  
    template <class _Tp>
    static void __test_noexcept(_Tp) _NOEXCEPT;
  
    static const bool value = noexcept(_ThisT::__test_noexcept<_Ret>(  // 431
        _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)));
};    
  
template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, true, _Ret, _Fp, _Args...>
{
    static const bool value = noexcept(                                 / 438
        _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)); 
};

[philnik]

In D140731#4021229, @Mordante wrote:

In D140731#4020155, @philnik wrote:

Where does this fire? noexcept(cond) should never be used in C++03.

include/__functional/invoke.h lines 431 and 438 are the only two places

template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, false, _Ret, _Fp, _Args...>
{
    typedef __nothrow_invokable_r_imp _ThisT;
  
    template <class _Tp>
    static void __test_noexcept(_Tp) _NOEXCEPT;
  
    static const bool value = noexcept(_ThisT::__test_noexcept<_Ret>(  // 431
        _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)));
};    
  
template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, true, _Ret, _Fp, _Args...>
{
    static const bool value = noexcept(                                 / 438
        _VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)); 
};

IMO we should fix the code here. In C++03 the values are always false anyways, so we could just make this

template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, false, _Ret, _Fp, _Args...>
{
    typedef __nothrow_invokable_r_imp _ThisT;
  
    template <class _Tp>
    static void __test_noexcept(_Tp) _NOEXCEPT;

#ifdef _LIBCPP_CXX03_LANG
    static const bool value = false;
#else
    static const bool value = noexcept(_ThisT::__test_noexcept<_Ret>(_VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)));
#endif
};    
  
template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, true, _Ret, _Fp, _Args...>
{
#ifdef _LIBCPP_CXX03_LANG
    static const bool value = false;
#else
    static const bool value = noexcept(_VSTD::__invoke(declval<_Fp>(), declval<_Args>()...)); 
#endif
};

or something similar.

[Mordante]

Uses an alternative approach as suggested by philnik.

[philnik]

LGTM with green CI.

libcxx/test/tools/clang_tidy_checks/robust_against_adl.cpp

 #include <algorithm>
 
 namespace {
 AST_MATCHER(clang::UnresolvedLookupExpr, requiresADL) { return Node.requiresADL(); }
 
 AST_MATCHER(clang::CallExpr, isOperator) { return llvm::isa<clang::CXXOperatorCallExpr>(Node); }
 
 AST_MATCHER(clang::UnresolvedLookupExpr, isCustomizationPoint) {
+  // In C++03 there is no noexcept operator. This is used in libc++, to avoid
+  // warnings pretend noexcept is a customization point.
   return std::ranges::any_of(
-      std::array{"swap", "make_error_code", "make_error_condition", "begin", "end", "size", "rend", "rbegin"},
+      std::array{
+          "swap", "make_error_code", "make_error_condition", "begin", "end", "size", "rend", "rbegin", "noexcept"},
       [&](const char* func) { return Node.getName().getAsString() == func; });
 }
 
 AST_MATCHER(clang::CXXMethodDecl, isStatic) { return Node.isStatic(); }
 
 } // namespace
 
 namespace libcpp {

libcxx/utils/ci/run-buildbot

check-generated-output)
     # Reject code with trailing whitespace
     ! grep -rn '[[:blank:]]$' libcxx/include libcxx/src libcxx/test libcxx/benchmarks || false
 ;;
 #
 # Various Standard modes
 #
 generic-cxx03)
     clean
-    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx03.cmake"
-    #generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx03.cmake" \
-    #               -DLIBCXX_ENABLE_CLANG_TIDY=ON
+    generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx03.cmake" \
+                   -DLIBCXX_ENABLE_CLANG_TIDY=ON
     check-runtimes
     check-abi-list
 ;;
 generic-cxx11)
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx11.cmake" \
                    -DLIBCXX_ENABLE_CLANG_TIDY=ON
     check-runtimes