Test/lldb

[hturner]

Opening this PR just to document the changes on this test branch, which demo a prototype LLDB setup.

You can try it out by building and running locally as described in the docs for local setup, but switching to the test/lldb branch before launching vscode.

Then:

1. Compile allow_ptrace.c

   gcc -shared -fPIC -o allow_ptrace.so allow_ptrace.c
   

2. Make the launch_r script executable

   chmod +x /workspaces/r-dev-env/scripts/launch_r.sh
   

   At this stage you should be able to open an R terminal, which will use the pre-built version of R. Running Sys.getenv("LD_PRELOAD") should show `"/workspaces/r-dev-env/scripts/allow_ptrace.so"). Quit R.
3. Build R from source as usual (optionally setting CFLAGS="-g -O0" before the configure step).
4. Manually switch from the inbuilt version of R to the one you just built by editing the launch.sh script:

   # exec /workspaces/r-dev-env/build/r-devel/bin/R "$@"
   exec /usr/bin/R "$@"
   

   i.e. uncomment the one you want, comment the one you don't want
5. Open a new R terminal. It should use the new version of R and show the same value for Sys.getenv("LD_PRELOAD") .
6. Start debugging with LLDB:
   • Run Sys.getpid() to get the process ID of R.
   • From the Run and Debug panel run "(lldb) Attach to R", input the pid to attach to the R process.
   • Set a breakpoint on a C file in the local copy of the sources, e.g. $TOP_SRCDIR/src/nmath/rgamma.c
   • Run code using that function e.g. rgamma(5,1) and the debugger will start.

Tested on Ubuntu 24.04 with fresh checkout from devel branch:

Note that debugger will not work for the pre-built version of R, as it was installed from a binary and we don't have access to the source files!

To get this working nicely we would want to do steps 1 and 2 as part of the devcontainer setup. Step 4 should be done by the which_r script - not by simply editing comments, but dynamically switching the path to the R executable, in a similar way to how we currently switch the path in the vscode settings:

r-dev-env/scripts/which_r.sh

Lines 63 to 64 in 46b8b6c

	updated_settings_data=$(cat "$settings_file_path" | jq --arg subdir "$selected_version" '."r.rterm.linux"=$subdir | ."r.rpath.linux"=$subdir')
	echo "$updated_settings_data" > "$settings_file_path"

After running the debugger we get a new button in the status bar labelled "(lldb) Attach to R (r-dev-env)" that you can use to select and start the debug configuration. This is okay, but it hides the "R: (not attached)" button. So either people need to hide some more things in the Status bar, or open R via the command palette. We would probably need to say something about this in the docs.

[hturner]

I commented out this line and added a .gitignore file to make it easier to share my changes here. I think we still want to delete the .git in the container to avoid confusing users.

[hturner]

Closing this, as we are getting closer on #267 now