Commit 1df2116b authored by Stephen Kelly's avatar Stephen Kelly
Browse files

Features: Decay language flag if requested is not available.

Use the highest standard compile flags available if requested language
version is too new.

This supports use-cases like

 set(CMAKE_CXX_STANDARD 14)

 # Compiled with -std=c++11 with GNU 4.7, which has no -std=c++14
 # or equivalent flag
 add_executable(main main.cpp)

This can be used in combination with preprocessor defines which
communicate the availability of certain language features for
optional use.
parent c4f4dac2
CXX_STANDARD
------------
The C++ standard whose features are required to build this target.
The C++ standard whose features are requested to build this target.
This property specifies the C++ standard whose features are required
This property specifies the C++ standard whose features are requested
to build this target. For some compilers, this results in adding a
flag such as ``-std=c++11`` to the compile line.
Supported values are ``98`` and ``11``.
If the value requested does not result in a compile flag being added for
the compiler in use, a previous standard flag will be added instead. This
means that using:
.. code-block:: cmake
set_property(TARGET tgt PROPERTY CXX_STANDARD 11)
with a compiler which does not support ``-std=c++11`` or an equivalent
flag will not result in an error or warning, but will instead add the
``-std=c++98`` flag if supported.
This property is initialized by the value of
the :variable:`CMAKE_CXX_STANDARD` variable if it is set when a target
is created.
......@@ -24,6 +24,8 @@ elseif(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.3)
set(CMAKE_CXX11_EXTENSION_COMPILE_OPTION "-std=gnu++0x")
endif()
set(CMAKE_CXX_STANDARD_DEFAULT 98)
macro(cmake_record_cxx_compile_features)
macro(_get_gcc_features std_version list)
record_compiler_features(CXX "-std=${std_version}" ${list})
......
......@@ -2152,8 +2152,8 @@ AddCompilerRequirementFlag(std::string &flags, cmTarget* target,
return;
}
std::string stdProp = lang + "_STANDARD";
const char *standard = target->GetProperty(stdProp);
if (!standard)
const char *standardProp = target->GetProperty(stdProp);
if (!standardProp)
{
return;
}
......@@ -2161,12 +2161,46 @@ AddCompilerRequirementFlag(std::string &flags, cmTarget* target,
bool ext = target->GetPropertyAsBool(extProp);
std::string type = ext ? "EXTENSION" : "STANDARD";
std::string compile_option =
"CMAKE_" + lang + std::string(standard)
+ "_" + type + "_COMPILE_OPTION";
if (const char *opt = target->GetMakefile()->GetDefinition(compile_option))
static std::map<std::string, std::vector<std::string> > langStdMap;
if (langStdMap.empty())
{
this->AppendFlags(flags, opt);
// Maintain sorted order, most recent first.
langStdMap["CXX"].push_back("11");
langStdMap["CXX"].push_back("98");
}
std::string standard(standardProp);
std::vector<std::string>& stds = langStdMap[lang];
std::vector<std::string>::const_iterator stdIt =
std::find(stds.begin(), stds.end(), standard);
assert(stdIt != stds.end());
const char* defaultStd
= this->Makefile->GetDefinition("CMAKE_" + lang + "_STANDARD_DEFAULT");
std::vector<std::string>::const_iterator defaultStdIt;
if (defaultStd)
{
defaultStdIt = std::find(stds.begin(), stds.end(), defaultStd);
assert(defaultStdIt != stds.end());
}
else
{
defaultStdIt = stds.end() - 1;
}
for ( ; stdIt <= defaultStdIt; ++stdIt)
{
std::string option_flag =
"CMAKE_" + lang + *stdIt
+ "_" + type + "_COMPILE_OPTION";
if (const char *opt = target->GetMakefile()->GetDefinition(option_flag))
{
this->AppendFlags(flags, opt);
return;
}
}
}
......
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