Nested namespaces (or C++1z) support

[mdziekon]

Hi, I'm currently trying to configure VSCode to "support" nested namespaces in C++ code. My code builds just fine when using clang++ (ver. 3.8.0) with flag -std=c++1z, so the only thing I need is working code completion inside VSC itself.

Is there a way to enable VSCode to use that "experimental" standard by switching some kind of configuration flag, or is this currently out of scope?

[sean-mcmanus]

What type of support are you looking for from VS Code? What feature is not working correctly? Are you referring to C++11 inline namespaces?

[mdziekon]

Consider the following code piece:

namespace my::nested::space {
    class some_class {
        ...
    };
}

In C++17, this is a valid definition of a nested namespace.

Currently, VSC with cpptools will throw the following error at the first line of this snippet:

severity: 'Error'
message: 'qualified name is not allowed'

... and of course I'm not able to autocomplete this namespace, nor the class name.

---

I guess VSC should be able to properly recognize this as a valid syntax, and properly detect some_class as a member of my::nested::space when trying to use autocompletion.

I'm not sure if this is something that is implemented inside the cpptools or provided by an external tool (like clang), but I hope this clarifies what I was trying to "achieve".

[sean-mcmanus]

The C++17 nested namespace feature doesn't even work with the Visual Studio 2017 IntelliSense, although the cl.exe compiler seems to support it. Our goal is to support C++17, but currently our level of support is around C++14. I'm not sure yet what the timeframe is.

[sean-mcmanus]

My previous statement is incorrect. Nested namespace definitions work in VS 2017 when the /std:c++latest compile flag is used, and it works in VS Code on Windows -- I'm reproing the error you're seeing on Linux. So it looks like a bug.

[sean-mcmanus]

The bug is "fixed" by adding , "-D_MSC_EXTENSIONS" to the end of the "defaults" array in ~/.vscode/extensions/ms-vscode.cpptools-0.11.0/bin/msvc.json . However, I'm not sure yet if that change has any other unwanted consequences (i.e. incorrect error squiggles) so we need to investigate it more. If you can test that change and let us know if you encounter any regressions that would help.

[mdziekon]

@sean-mcmanus Thank you for your response. I can confirm that this quick "fix" allowed me to use nested namespaces. However (just a note for other people struggling with the same problem), I had to apply this change to the msvc.json file to make it work:

{
    "match": "^/lang_cpp_",
    "replace": "--c++latest"
}

(previous value of replace key was c++14).

I'll test that out and report any problems once found.

[sean-mcmanus]

Using "c++latest" as described should not work -- hovering should give an error message about "No IL available". It probably looks like it worked because the error disappeared because the invalid flag causes the errors to go away. Can you try the other , "-D_MSC_EXTENSIONS" fix? The c++14 is the latest flag that is supported by us and the c++17 flag behaves identically. From what I understand, the Microsoft compilers added the nested namespace definition feature in VS 2015 as an extension before C++17 was finished.

[mdziekon]

At first, I've applied only the , "-D_MSC_EXTENSIONS" fix, and unfortunately nothing has changed.
You're probably right about the --c++latest being a placebo. I was under the impression that this indeed did work, because I saw working autocompletion, which turned out to work even without all these changes.

Btw, I forgot to mention that I'm using VSCode Insiders, here is the exact version number:

Version 1.13.0-insider
Commit 674200fd49ad8c1557f884903fd09647975270f8
Date 2017-05-08T06:08:43.536Z
Shell 1.6.6
Renderer 56.0.2924.87
Node 7.4.0

[sean-mcmanus]

Yeah, I was mistaken. For some strange reason, simply adding a comma to the end of the "defaults" list causes it to become "fixed" (not the "-D_MSC_EXTENSIONS" mentioned earlier, e.g. "-D_USE_DECLSPECS_FOR_SAL=1",). I'm not able to detect a negative side effect from this change yet though (I'm getting correct IntelliSense errors and hover results). And the change needs to be made in the .vscode-insiders folder for insiders.

[mdziekon]

Simply placing , at the end of the array breaks standard libraries includes - VSCode cannot resolve includes like #include <vector> (which were previously working just fine).
It also throws 'name followed by '::' must be a class or namespace name' when trying to use a class from that nested namespace, but that might be broken because of other problems (mentioned includes) inside that file.

[sean-mcmanus]

Okay, you're right, I'm able to repro the problem with vector. We need to investigate further why this is working on Windows and not Linux.

[sean-mcmanus]

Changing "replace": "--c++14" to "replace": "--c++17" in the msvc.json fixes the issue. I didn't think we had any C++17 support, but it looks like we support namespace attributes, nested namespace definitions, enumerator attributes, terse static assert, and possibly utf8 char literals and relaxed range-based for (not sure about the last two). But more C++17 is expected later.

[mdziekon]

I can confirm it works as expected (this time, introducing any kind of error in other places of the code properly displays that, so the language server works fine). Thank you for your response and investigation.

[bobbrow]

This was fixed in version 0.11.1. Please reopen if you continue to have this issue.