Can't complete any C++ system headers and only some C system headers but jumping to their definition works

[bfrg]

I'm on Gentoo Linux using ccls through vim-lsp. Further system info see below.

Issues

ccls doesn't find any C++ system headers and only a few C system headers:

Completion of std::vector doesn't work:

But completing a std::vector method or nested type works:

Completing the methods of a std::vector instance works, too:

Jumping to the definition of std::vector (or any of its methods) works, too:

System info

This is how I built ccls:

$ mkdir build && cd build
$ cmake .. -DSYSTEM_CLANG=on -DCMAKE_PREFIX_PATH=/usr/lib/llvm/7 -DLLVM_ENABLE_RTTI=on
$ make -j4

My system include directories (output of clang -E -v -xc++ /dev/null):

/usr/include/c++/v1
/usr/lib64/llvm/7/bin/../../../../lib/clang/7.0.0/include
/usr/include

$ clang++ -print-resource-dir
/usr/lib64/llvm/7/bin/../../../../lib/clang/7.0.0

This issue is similar to #37.

[MaskRay]

This issue is similar to #37.

It is different. See my comment at #37 (comment)

From your clang -E -v -xc++ /dev/null output, /usr/include/c++/v1 indicates your clang uses libc++ for its -stdlib=platform. Are you using default-libcxx?

libstdc++

Can you try this .ccls configuration?

clang++
-stdlib=libstdc++

Alternatively, set the initialization option clang.extraArgs, e.g.

• command line: ccls -index ~/project -init='{"clang":{"extraArgs": ["--stdlib=libstdc++"]}}'
• client setting: check out how to pass initialization options

libc++

See https://github.com/llvm-mirror/clang/tree/master/lib/Driver/ToolChains/Linux.cpp#L872

void Linux::addLibCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                  llvm::opt::ArgStringList &CC1Args) const {
  const std::string& SysRoot = computeSysRoot();
  const std::string LibCXXIncludePathCandidates[] = {
      DetectLibcxxIncludePath(getDriver().ResourceDir + "/include/c++"),
      DetectLibcxxIncludePath(getDriver().Dir + "/../include/c++"),
      // If this is a development, non-installed, clang, libcxx will
      // not be found at ../include/c++ but it likely to be found at
      // one of the following two locations:
      DetectLibcxxIncludePath(SysRoot + "/usr/local/include/c++"),
      DetectLibcxxIncludePath(SysRoot + "/usr/include/c++") };

In a debug session, I find the 4 DetectLibcxxIncludePath calls all return "".

DetectLibcxxIncludePath(SysRoot + "/usr/include/c++") is empty for my case because I have not installed system libc++ headers. After some investigation, I find I can do:

c-index-test -code-completion-at=a.cc:7:10 -stdlib=libc++ a.cc -ccc-install-dir ~/llvm/Release/bin -resource-dir=~/llvm/Release/lib/clang/8.0.0

ccc-install-dir should point to your clang installation directory (getDriver().Dir)

BTW, if you use clang 8, its clangSema implements a native #include completion which ccls uses to replace include_complete.cc.

[bfrg]

Yes, I do have the default-libcxx USE flag enabled and ccls jumps to the correct std::vector definition (see last screenshot).

libstdc++

I've added the -stdlib=libstdc++ option and completion works better now, but it still won't list all system include headers.

libc++

Running c-index-test (cursor at #include <s▎, see first screenshot):

c-index-test -code-completion-at=main.cpp:3:12 -stdlib=libc++ main.cpp -ccc-install-dir /usr/lib64/llvm/7/bin -resource-dir /usr/lib/clang/7.0.0

outputs:

Completion contexts:
Unknown
Any type
Any value
Objective-C object value
Objective-C selector value
C++ class type value
Dot member access
Arrow member access
Objective-C property access
Enum tag
Union tag
Struct tag
Class name
Namespace or namespace alias
Nested name specifier
Objective-C interface
Objective-C protocol
Objective-C category
Objective-C instance method
Objective-C class method
Objective-C selector name
Macro name
Natural language

[MaskRay]

@bfrg #include completion is available in clang 8. The just released clang 7 does not include the feature.

I've added the -stdlib=libstdc++ option and completion works better now, but it still won't list all system include headers.

Check the output of clang -E -v -stdlib=libstdc++ -xc++ /dev/null and https://github.com/llvm-mirror/clang/tree/master/lib/Driver/ToolChains/Linux.cpp

Adding -ccc-install-dir /usr/lib64/llvm/7/bin also helps. I still believe think it is likely a configuration issue. If (very unlikely) that is not the case, use -isystem

You can find relevant -isystem options with clang -fsyntax-only '-###' -stdlib=libstdc++ -xc++ /dev/null

[bfrg]

The #include completion isn't so important. I have my own small C preprocessor completion for Vim that works fine. I will just wait until Clang 8 is available on Gentoo Linux.

I have removed libc++ from my system since I don't need it anyway. This is now the output of the preprocessor:

$ clang -E -v -xc++ /dev/null
 /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/include/g++-v8
 /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/include/g++-v8/x86_64-pc-linux-gnu
 /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/include/g++-v8/backward
 /usr/lib64/llvm/7/bin/../../../../lib/clang/7.0.0/include
 /usr/include

The followings works (▎is the cursor position where I start the completion):

#include <vector>

int main()
{
    std::v▎
    std::vector<int> v{1,2,3};
}

ccls will list two candidates:

vector<typename _Tp>   class
vector<typename _Tp, typename _Alloc>   class

But when I start the completion below the vector instantiation:

#include <vector>

int main()
{
    std::vector<int> v{1,2,3};
    std::v▎
}

ccls will list void_t<typename> class as the only completion candidate.

Then, when I go back and try to complete above the line std::vector<int> v{1,2,3}; (as before), the completion menu will list only valarray<typename _Tp> class.
I'm not sure if that's ccls or vim-lsp that is causing this behavior.

[MaskRay]

You may use strace/sysdig to dump LSP requests/responses
https://github.com/MaskRay/ccls/wiki/Debugging#dump-lsp-requestsresponses

#include <vector>

int main()
{
    std::vector<int> v{1,2,3};
    std::▎  // trigger textDocument/completion manually, is `vector` on the list?
}

[bfrg]

I've tried it with VS Code using your ccls extension and everything works fine. So it's definitively the language server client that I'm using (vim-lsp).

Thank you for your help!

[avnotaklu]

I had gcc 12 installed but did not have libstdc++ for it.
I worked after installing it using
sudo apt install libstdc++-12-dev