Header-only IntelliSense should use language ID delivered with `didOpen` instead of defaulting to C++

[JAicewizard]

Bug type: Language Service

Describe the bug

• OS and Version: linux 5.17.1
• VS Code Version: 1.65.2
• C/C++ Extension Version: 1.9.7
• Other extensions you installed (and if the issue persists after disabling them): dart, go, flutter, python, rust (literal names of the extensions)
• If using SSH remote, specify OS of remote machine:
• A clear and concise description of what the bug is, including information about the workspace (i.e. is the workspace a single project or multiple projects, size of the project, etc). Workspace is a project with a lot of go code and one file in c, a header file with just one line. This file is located at x/y.h. and contains void z(char *restrict q); which is valid C code. Language is set to C.

Steps to reproduce

1. Open x/y.h
2. See error

Expected behavior No squiggly lines

Code sample and logs

• Code sample

  void z(char *restrict q);

• Configurations in c_cpp_properties.json

• Logs from running C/C++: Log Diagnostics from the VS Code command palette

  
  -------- Diagnostics - 04/04/2022, 19:07:04
  Version: 1.9.7
  Current Configuration:
  {
  "name": "Linux",
  "includePath": [
      "${workspaceFolder}/**"
  ],
  "defines": [],
  "compilerPath": "/sbin/clang",
  "cStandard": "c17",
  "cppStandard": "c++14",
  "intelliSenseMode": "linux-clang-x64",
  "compilerArgs": [],
  "intelliSenseModeIsExplicit": false,
  "cStandardIsExplicit": false,
  "cppStandardIsExplicit": false,
  "mergeConfigurations": false,
  "compilerPathIsExplicit": false,
  "browse": {
      "path": [
          "${workspaceFolder}/**"
      ],
      "limitSymbolsToIncludedHeaders": true
  }
  }
  Translation Unit Mappings:
  [ /.../x/y.h ]:
  /.../x/y.h
  Translation Unit Configurations:
  [ /.../x/y.h ]:
  Process ID: 17136
  Memory Usage: 12 MB
  Compiler Path: /sbin/clang
  Includes:
      /usr/include/c++/11.2.0
      /usr/include/c++/11.2.0/x86_64-pc-linux-gnu
      /usr/include/c++/11.2.0/backward
      /usr/lib/clang/13.0.1/include
      /usr/local/include
      /usr/include
  Standard Version: c++14
  IntelliSense Mode: linux-clang-x64
  Other Flags:
      --clang
      --clang_version=130001
      --header_only_fallback
  Total Memory Usage: 12 MB

------- Workspace parsing diagnostics ------- Number of files discovered (not excluded): 26971 Number of files parsed: 3712

• Logs from the language server logging loggingLevel: Debug loggingLevel has changed to: Debug cpptools/didChangeCppProperties $/setTraceNotification cpptools/getCodeActions: /.../x/y.h (id: 149) cpptools/textEditorSelectionChange cpptools/textEditorSelectionChange cpptools/activeDocumentChange: /.../x/y.h cpptools/getFoldingRanges: /.../x/y.h (id: 150) cpptools/getCodeActions: /.../x/y.h (id: 151) textDocument/didClose: /.../x/y.h Database safe to open cpptools/getCodeActions: /.../x/y.h (id: 152) textDocument/didOpen: /.../x/y.h Checking for syntax errors: /.../x/y.h Queueing IntelliSense update for files in translation unit of: /.../x/y.h cpptools/textEditorSelectionChange cpptools/getDocumentSymbols: /.../x/y.h (id: 153) cpptools/textEditorSelectionChange cpptools/getSemanticTokens: /.../x/y.h (id: 154) cpptools/getDocumentSymbols cpptools/activeDocumentChange: /.../x/y.h cpptools/getFoldingRanges: /.../x/y.h (id: 155) cpptools/getCodeActions: /.../x/y.h (id: 156) cpptools/finishUpdateSquiggles Error squiggle count: 1 terminating child process: 18585 Update IntelliSense time (sec): 0.367 cpptools/getCodeActions: /.../x/y.h(id: 157) cpptools/getFoldingRanges: /.../x/y.h (id: 158) cpptools/textEditorSelectionChange cpptools/activeDocumentChange: /.../x/y.h

[Colengms]

Hi @JAicewizard . By default, when a .h file is opened and there is no source file (.cpp, .c, etc.) to associate it with, the C/C++ extension treats the file as containing C++ code. I don't believe the restrict keyword is supported in C++. Note this comment in the C++ specification.

I believe you could work around the issue if you add a .c file that includes that header. That .c file should be found when opening the header, and the header would be interpreted as containing C code instead of C++ code.

Does that resolve your issue?

[JAicewizard]

That does "fix" the issue, but I have explicitly set the language to C, not C++.

So it is probably the case that the the language server misinterprets the file even though I told VScode explicitly that this is a C file.

[Colengms]

Hi @JAicewizard . Thanks. We'll use this issue to track addressing that. In the meanwhile, it would also be possible to work around the issue by setting a file association in settings, like so:

{
    "files.associations": {
        "test.h": "c"
    }
}

[JAicewizard]

Yup this seems to work, even though vscode is now telling me it is in C++ mode, the c/c++ extension seems to be in C mode now. Maybe there is something not working with the language mode in vscode? Or maybe it doesnt do what I expect it to do.

[sean-mcmanus]

Yeah, it seems like we may not be responding correctly to C versus C++ language mode changes from the status bar. I filed an issue at https://github.com/microsoft/vscode-cpptools/issues/9141 .