cmssw_vscode

Recipies to develop CMSSW using VSCode

Contents:

• Indexing files: C++ source navigation and setup using clangd
• ROOT files: View ROOT files directly in VSCode
• Fix VSCode SSH Connection Errors with AFS: Avoid having to manually delete .vscode-server every time your connection drops

This AFS-related SSH bug tends to come back periodically — especially when your internet connection is unstable or slow — so it's definitely worth applying the fix described at the end.

Indexing files

Indexing files allows VSCode to easily resolve references to imported files. This provides:

• go to definition

  

• find references

  

• errors and warnings detection

  

More details and features in the VSCode and clangd documentations.

C++

Indexing C++ files is based on the clangd extension alongside a compile-commands.json file.

1. Install clangd.
   1. In VSCode in the side bar go to Extensions.
   2. In the search bar type clangd.
   3. Click Install.
   4. Click Install in SSH: lxplus.cern.ch.
   5. Disable IntelliSense if you have to installed (comes with the C/C++ Microsoft extension).
      1. In VSCode press Ctrl + Shift + P, type Preferences: Open Settings (UI) and click Enter.
      2. Switch to Remote [SSH: lxplus.cern.ch].
      3. In the search bar type C_Cpp.intelliSenseEngine.
      4. Switch to disabled.
2. Initialize your CMSSW release environment: execute cmsenv in the src subdirectory of your CMSSW repo. This will add two additional environment variables:
   • CMSSW_RELEASE_BASE: path to the CMSSW repo on the CVMFS shared network file system.
   • CMSSW_BASE: path to your locally cloned CMSSW repo.
3. Point clangd to the compile_commands.json file. VSCode will look for it on the CMSSW_BASE path, regardless which subdirectory you open. A couple of options exist:
   • Add the directory with the file to the clangd settings:
     1. In your terminal with the environment set up get the value of CMSSW_RELEASE_BASE:

        [tostafin@lxplus960 src]$ echo $CMSSW_RELEASE_BASE
        /cvmfs/cms.cern.ch/el9_amd64_gcc12/cms/cmssw/CMSSW_14_0_6
        

     2. In VSCode press Ctrl + Shift + P, type Preferences: Open Settings (UI) and click Enter.
     3. Switch to Remote [SSH: lxplus.cern.ch].
     4. In the search bar type clangd.arguments.
     5. Add a new argument: --compile-commands-dir=<value-of-CMSSW_RELEASE_BASE>. For instance using the value above: --compile-commands-dir=/cvmfs/cms.cern.ch/el9_amd64_gcc12/cms/cmssw/CMSSW_14_0_6.
   • Create a symbolic link to the file: in your terminal with the environment set up execute ln -s $CMSSW_RELEASE_BASE/compile_commands.json $CMSSW_BASE.
   • Copy the file: in your terminal with the environment set up execute cp $CMSSW_RELEASE_BASE/compile_commands.json $CMSSW_BASE.
4. Restart the clangd server. Press Ctrl + Shift + P, type clangd: Restart language server and click Enter.

Note: you don't have to wait for all files to be indexed to use clangd features.

ROOT files

ROOT is a data analysis framework used for visualizing large amounts of data using histograms, scatter plots etc.

ROOT File Viewer

These graphics can be viewed in VSCode using the ROOT File Viewer extension.

1. Install ROOT File Viewer
   1. In VSCode in the side bar go to Extensions.
   2. In the search bar type ROOT File Viewer.
   3. Click Install.
2. Open a ROOT file by left-clicking on it in the Explorer tab.
3. Select a graphic to display.

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Fix VSCode SSH Connection Errors with AFS

If you connect to a remote machine using AFS (Andrew File System), you might encounter a recurring bug that forces you to delete the .vscode-server folder from the remote every time you want to reconnect.

The Fix

1. Create a dedicated folder for VSCode server files in your EOS home directory.

   Suppose your username is jkowal, run the following command on the remote machine:

   mkdir -p /eos/user/j/jkowal/vscode-server

2. Remove the existing .vscode-server from your AFS home directory.

   rm -r ~/.vscode-server

3. Create a symbolic link pointing from your AFS home directory to the new folder.

   ln -s /eos/user/j/jkowal/vscode-server ~/.vscode-server