Alberto Pérez de Rada Fiol

Alberto Pérez de Rada Fiol

Alberto is maintaining the ROOT File Viewer VS Code extension.

How to run ROOT Macros in VS Code

(31 March 2021)

Visual Studio Code offers some great functionalities when it comes to coding, such as IntelliSense, debugging, built-in Git, and many more through extensions. In this blog post I’m going to show how to configure VS Code in order to use all of these awesome features when creating and editing ROOT Macros!

A few weeks ago, I published a blog post about ROOT File Viewer, an extension to view ROOT Files directly in VS Code. On the discussion of said post the question of how to run ROOT Macros in VS Code arose, and I came up with an example repository to show how that can be accomplished. Let us now walk through this example repository and see how everything works.

Get it running

To get started, we will start cloning and opening the repository. This can be done from the command line with:

git clone https://github.com/AlbertoPdRF/root-on-vscode.git
cd root-on-vscode
code .

After this is done, we need to manually set the path to our local ROOT installation in two files. We can do that quickly with the editor’s convenient global search and replace functionality:

  1. Toggle the global Search view with Ctrl + Shift + F or clicking on the Search icon in the Activity Bar
  2. Search for /home/apdrf/programs/root-6.22/install, two occurrences should show up
  3. Toggle Replace by clicking on the caret on the left of the Search input box
  4. Write the path to your local ROOT installation directory on the Replace input box
  5. Replace the two occurrences with Ctrl + Alt + Enter or clicking on Replace All on the right of the input box

We are almost ready to see everything in action, so let us open the workspace and get to it! There’s a few ways to do that, but probably the simplest one to do it is to:

  1. Open the file root-on-vscode.code-workspace, which is located inside the .vscode folder
  2. Click on the blue button at the bottom right of the editor that reads Open Workspace

After we have opened the workspace, a toast notification will appear at the bottom right of the editor asking us if we want to install the recommended extensions for the repository. Clicking on the Install button will install both the C/C++ and ROOT File Viewer extensions. Please note that the second one is not strictly required for everything to work, it is just listed as a recommendation for convenience.

And that is everything that is needed! Just press F5 and see it for yourself: the example hsimple.C ROOT Macro will run and the hsimple.root file will be recreated.

With everything running, we can now take advantage of some of the awesome functionalities that we mentioned before to develop our ROOT Macros, for instance:

  • Use IntelliSense’s smart completions to easily create and edit macros without fear of getting the syntax wrong
  • Debug the macros right from the editor setting break points, seeing call stacks, and with an interactive console available
  • Use the integrated clang-format to always get our code styled as we want it
  • And there’s much more!

But I know this all feels like magic, so if you want to know how everything works, keep reading!

How it works

What we do in this example is to define a VS Code Workspace with the necessary configuration for everything to work, so let us first see what a workspace is and how it is configured.

A VS Code Workspace is simply a collection of (one or more) folders that are opened in a VS Code instance (a window). For this example, we have defined a root-on-vscode workspace through the root-on-vscode.code-workspace JSON file located on the .vscode folder. Said file contains the following configuration:

  • folders: here we define the path to our workspace folder(s), relative to the location of this same file
  • settings: through this object we tell VS Code to treat files with the .C extension as C++ files and the path where it has to search for our header files, which in this case is ROOT’s include directory
  • extensions: here is were we recommend for the C/C++ and ROOT File Viewer extensions to be installed for this workspace

Apart from configuring the settings of the workspace, we have also defined a launch configuration, which is how we are going to be able to run ROOT Macros directly within VS Code. This is done in the launch.json file, also located on the .vscode folder. From this file I will just mention a few of its key points:

  • We will use the gdb debugger under the hood
  • The program that we will launch is the root.exe executable
  • We will pass everything necessary to ROOT’s executable as arguments (which of course can be tweaked at will), as we would do on the command line:
    • -l to avoid showing ROOT’s banner
    • -q so the program quits after it finishes processing the macro
    • hsimple.C+g to tell the program which macro to run and to compile it with debugging symbols – this is what allows us to set break points through the macro

And this is basically it, the rest of the things that the repository includes are:

  • A very basic .gitignore file to not commit compilation artifacts to the repository
  • The hsimple.C macro from ROOT Tutorials
  • The resulting hsimple.root file
  • And a README.md file with some basic information

Summary

With this blog post I just wanted to quickly illustrate how we can configure VS Code to run ROOT Macros directly in it. Doing so allows us to take advantage of some great functionalities of the editor that will make our lives way easier, and this way we can focus on what truly matters!