Debug in Skink: breakpoints, stepping and variables (DAP)

Press F9 on a line to set a breakpoint, then F5 to start. Skink picks a configuration for you, or asks when there are several. When the program stops, step with F10, F11 and Shift+F11.

Skink speaks the Debug Adapter Protocol, so it drives the same debuggers VS Code uses.

Debug keys

Key	Typed command	Does
`F5`	`:continue`	Start (the last configuration, else pick one), or continue
`Shift`+`F5`	`:debug stop`	Stop the program (press again to kill the adapter)
`F10`	`:step`	Step over
`F11`	`:stepin`	Step into
`Shift`+`F11`	`:stepout`	Step out
`F6`	`:pause`	Pause the running program
`F9`	`:breakpoint`	Breakpoint on the cursor line, on or off
`Alt`+`F9`	`:condition`	Condition, hit count or log message for that breakpoint
`Alt`+`L`	`:debug panel`	The debug panel
`Alt`+`K`	`:hover`	While paused: the value at the cursor

Outside a debug session, F10, F11, Shift+F11 and F6 keep their usual jobs: the menu bar, close the terminal, terminal history and next problem.

Clicking the sign column also toggles a breakpoint.

Install a debug adapter

Skink finds the adapter on your PATH:

Adapter	For	`type` in launch.json
gdb 14 or newer (`gdb -i dap`)	C, C++, Rust, Zig	`gdb`
`lldb-dap`	C, C++, Rust (LLVM)	`lldb-dap`
`codelldb`	C, C++, Rust (CodeLLDB)	`lldb`
debugpy (`pip install debugpy`)	Python	`debugpy`
`dlv` (`dlv dap`)	Go	`go`

JavaScript debugging (js-debug) is not supported yet.

While the program is paused

The stopped line is highlighted.
Local values show at the ends of the lines above it.
Alt+K on a name shows its value.

The panel (Alt+L) holds the rest:

Part	Keys
Call stack	`Enter` shows a frame
Variables	`Enter` or `Space` expands
Watch	`w` adds, `d` removes
Breakpoints	`Enter` jumps, `d` removes
Console	`e` evaluates an expression

Programs that the adapter runs “in a terminal” open in a terminal tab, so you can type into them.

Conditions and logpoints

Put the cursor on a breakpoint’s line and press Alt+F9, or type one of:

Command	Does
`:breakpoint if i > 3`	Stop only when the condition holds
`:breakpoint hits 5`	Stop on the fifth hit
`:breakpoint log x={x}`	Print a message instead of stopping
`:breakpoint clear`	Remove every breakpoint in this file
`:breakpoint clearall`	Remove every breakpoint
`:breakpoint list`	List them

Breakpoints move with your edits, and the session remembers them and your watches.

Configurations

With no config file, F5 offers what it can find:

each cargo binary
the Python file or pytest test at the cursor
the Go package or test at the cursor
a native program built next to the file (cc -g x.c -o x)

For more control, write .skink/launch.json. An existing .vscode/launch.json works too.

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "server",
      "type": "gdb",
      "request": "launch",
      "program": "${workspaceFolder}/target/debug/server",
      "args": ["--port", "8080"],
      "preLaunchTask": "build"
    }
  ]
}

Skink reads this subset of VS Code’s format:

name, type, request (launch or attach)
preLaunchTask: a task label from tasks.json, run before the program starts
per-OS overrides under linux, osx and windows

Every other field goes to the adapter as written, with ${workspaceFolder}, ${file} and the other variables expanded.

Command	Does
`:debug`	Pick a configuration
`:debug NAME`	Start one by name
`:debug restart` / `:debug pause` / `:debug stop`	Control the session
`:debug eval EXPR`	Evaluate an expression
`:debug watch EXPR`	Add a watch