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cxxmodules: Fix CMP0155 NEW behavior when C++ compile features are not known

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With CMP0155 NEW behavior, we scan C++ sources in targets using C++ 20,
i.e., in which the `cxx_std_20` feature is available.  However, our
check for C++ feature availability may incorrectly succeed in two cases:

* MSVC versions from VS 2013 do not model C++ standard levels,
  so we assume all features are available as a heuristic to let
  projects at least try compiling with them.

* During ABI detection the `CMAKE_CXX20_COMPILE_FEATURES` variable is not
  populated so we assume all features are available, knowing that our
  ABI detection project does not need them.

For purposes of detecting targets using C++ 20, we do not want to assume
`cxx_std_20` is available, so verify that we really know it is.
This commit is contained in:
Brad King
2023-10-03 15:19:44 -04:00
parent 8bd2c8d1fd
commit 7ac696549a
1 changed files with 18 additions and 11 deletions
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29
Source/cmGeneratorTarget.cxx
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@@ -9093,20 +9093,27 @@ cmGeneratorTarget::Cxx20SupportLevel cmGeneratorTarget::HaveCxxModuleSupport(
if (!state->GetLanguageEnabled("CXX")) {
return Cxx20SupportLevel::MissingCxx;
}
cmValue standardDefault =
this->Target->GetMakefile()->GetDefinition("CMAKE_CXX_STANDARD_DEFAULT");
if (standardDefault && !standardDefault->empty()) {
cmStandardLevelResolver standardResolver(this->Makefile);
if (!standardResolver.HaveStandardAvailable(this, "CXX", config,
"cxx_std_20")) {
return Cxx20SupportLevel::NoCxx20;
}
this->Makefile->GetDefinition("CMAKE_CXX_STANDARD_DEFAULT");
if (!standardDefault || standardDefault->empty()) {
// We do not know any meaningful C++ standard levels for this compiler.
return Cxx20SupportLevel::NoCxx20;
}
// Else, an empty CMAKE_CXX_STANDARD_DEFAULT means CMake does not detect and
// set a default standard level for this compiler, so assume all standards
// are available.
cmStandardLevelResolver standardResolver(this->Makefile);
if (!standardResolver.HaveStandardAvailable(this, "CXX", config,
"cxx_std_20") ||
// During the ABI detection step we do not know the compiler's features.
// HaveStandardAvailable may return true as a fallback, but in this code
// path we do not want to assume C++ 20 is available.
this->Makefile->GetDefinition("CMAKE_CXX20_COMPILE_FEATURES")
.IsEmpty()) {
return Cxx20SupportLevel::NoCxx20;
}
cmValue scandepRule =
this->Target->GetMakefile()->GetDefinition("CMAKE_CXX_SCANDEP_SOURCE");
this->Makefile->GetDefinition("CMAKE_CXX_SCANDEP_SOURCE");
if (!scandepRule) {
return Cxx20SupportLevel::MissingRule;
}