Opened 8 years ago
Closed 5 years ago
#53634 closed defect (invalid)
clang++-mp-4.0 -stdlib=macports-libstdc++ should be in C++11 mode by default
Reported by: | mojca (Mojca Miklavec) | Owned by: | mojca (Mojca Miklavec) |
---|---|---|---|
Priority: | Low | Milestone: | |
Component: | ports | Version: | |
Keywords: | Cc: | MarcusCalhoun-Lopez (Marcus Calhoun-Lopez), larryv (Lawrence Velázquez), michaelld (Michael Dickens), jeremyhu (Jeremy Huddleston Sequoia), kencu (Ken) | |
Port: | clang-4.0 |
Description
Related to #53194, #53329, #53330.
Compare the following output on < 10.9:
> g++-mp-6 test.cpp -o test # OK
> clang++-mp-4.0 -stdlib=libc++ test.cpp -o test # OK
> clang++-mp-4.0 test.cpp -o test test.cpp:1:10: fatal error: 'regex' file not found #include <regex> ^~~~~~~ 1 error generated.
> clang++-mp-4.0 -stdlib=macports-libstdc++ test.cpp -o test In file included from test.cpp:1: In file included from /opt/local/include/gcc6/c++/regex:35: /opt/local/include/gcc6/c++/bits/c++0x_warning.h:32:2: error: This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options. #error This file requires compiler and library support \ ^ 1 error generated.
The file test.cpp
is a simple #include <regex> int main() { return 0; }
While this can be avoided by adding a -std=c++11
flag, the behaviour would be much more consistent if the compiler would assume C++11 by default.
See also #53625 where this first came up.
Change History (11)
comment:1 Changed 8 years ago by jeremyhu (Jeremy Huddleston Sequoia)
Owner: | changed from jeremyhu to mojca |
---|---|
Status: | new → assigned |
comment:2 Changed 8 years ago by jeremyhu (Jeremy Huddleston Sequoia)
Cc: | jeremyhu added |
---|
comment:3 Changed 8 years ago by mojca (Mojca Miklavec)
Marcus, since you were patching this, do you have any idea where/how to fix the behaviour? I'm not too familiar with llvm sources. I did some grep-ing for various variables, I found places like Opts.CPlusPlus11 = Std.isCPlusPlus11()
, but it's so much code that it's nearly impossible to know where the decision is made about whether or not C++11 should be the default.
comment:4 Changed 8 years ago by mojca (Mojca Miklavec)
Cc: | kencu added |
---|
comment:5 Changed 8 years ago by kencu (Ken)
I'm thinking that this bit in Marcus' patch:
+ case ToolChain::CST_MacPortsLibstdcxx: + if (getVFS().exists("@@MACPORTS_libstdc++@@")) { + CmdArgs.push_back("@@MACPORTS_libstdc++@@"); + return; + } + CmdArgs.push_back("-lstdc++"); + break;
could be this instead:
+ CmdArgs.push_back("-lstdc++"); + CmdArgs.push_back("-std=c++11");
Edit - the following did not work. -- Ken
there's another spot at the very end of the patch that does the same kind of push_back, and probably the same extra addition should go there, although the way it's written right now it might also affect CST_Libstdcxx and so we would need a separate break; item for each CST.
case ToolChain::CST_Libstdcxx: + case ToolChain::CST_MacPortsLibstdcxx: CmdArgs.push_back("-lstdc++"); break;
like this maybe:
case ToolChain::CST_Libstdcxx: CmdArgs.push_back("-lstdc++"); break; case ToolChain::CST_MacPortsLibstdcxx: CmdArgs.push_back("-lstdc++"); CmdArgs.push_back("-std=c++11"); break;
comment:6 Changed 8 years ago by kencu (Ken)
See below for the more likely area to patch, if desired.
comment:7 Changed 8 years ago by kencu (Ken)
It would be rather trivial to add
configure.cxxflags-append -std=c++11
in the right place in the cxx11 1.1 portgroup, as presumably any code that is calling that portgroup is c++11 compatible, after all.
comment:8 Changed 8 years ago by kencu (Ken)
There is a bit of logic in tools/clang/lib/Driver/Tools.cpp where the build line parsing logic looks for a std language standard to be set, and if there is none, appears to offer one up for c, but apparently not for c++ unless you're on Windows, if I read this correctly.
if (!types::isCXX(InputType)) Args.AddAllArgsTranslated(CmdArgs, options::OPT_std_default_EQ, "-std=", /*Joined=*/true); else if (IsWindowsMSVC) ImplyVCPPCXXVer = true;
ImplyVCPPCXXVer = true
leads to a block of code later down that sets a standard language on Windows. So far, this would seem to me to be the most likely place to add in a default c++ language standard, if a suitable test for darwin && stdlib=macports-libsdtc++ could be generated.
comment:9 Changed 8 years ago by kencu (Ken)
FYI, it looks like there was some recent discussion going on about defaulting to c++11 or c++14 on the clang developers mailing list: <http://clang-developers.42468.n3.nabble.com/Setting-default-dialect-to-C-11-td4055489.html>.
This thread is also germane to this topic <http://clang-developers.42468.n3.nabble.com/RFC-Default-language-standard-mode-policy-td4052354.html>.
comment:10 Changed 7 years ago by kencu (Ken)
See <https://reviews.llvm.org/D40948>. This commit changes the default language standard to c++14. It should be in the clang-6.0 release.
I was way off -- there is a one-liner to change the language standard that I didn't find.
comment:11 Changed 5 years ago by kencu (Ken)
Resolution: | → invalid |
---|---|
Status: | assigned → closed |
the llvm devs decided ath clang-7.0+ will default to c++17
I'm certainly fine letting -stdlib=macports-libstdc++ imply -std=c++11. Feel free to make that change. Of course, -stdlib=libstdc++ should not change.