DAP

Active contributors: kubkon, Anthony-Eid, osiewicz

Purpose

The DAP system implements a Debug Adapter Protocol client and the surrounding UI. It lets you start, control, and inspect debug sessions for any language with a DAP-compatible adapter.

Crates

Crate	Role
crates/dap	DAP client (transport + request types + lifecycle)
crates/dap_adapters	Per-language adapter wrappers
crates/debugger_ui	UI panels: variables, call stack, breakpoints, REPL
crates/debugger_tools	Dev helpers: DAP message inspector, fakes
crates/debug_adapter_extension	Extension-API surface for third-party adapters

Project::debugger_store owns the per-project DAP session registry; see Project.

Key abstractions

Type	File	Description
DebugAdapter	crates/dap/src/...	An LSP-style wrapper over a DAP-speaking process
DapStore / DebuggerStore	crates/project/src/debugger.rs	Per-project store of running adapters/sessions
Adapter registry	crates/dap_adapters	Maps language → adapter binary + transport
DebuggerPanel	crates/debugger_ui/src/...	The in-app debugger panel
BreakpointStore	crates/project/src/... (debugger area)	Breakpoints across files

How it works

sequenceDiagram
    participant U as User
    participant DP as DebuggerPanel
    participant DS as DebuggerStore
    participant A as DebugAdapter
    participant P as Adapter process

    U->>DP: Start debug "Run main"
    DP->>DS: launch(config)
    DS->>A: spawn adapter
    A->>P: stdio DAP
    A-->>DS: initialized
    DS->>A: setBreakpoints
    DS->>A: launch
    A-->>DP: stoppedEvent
    DP->>DS: continue / step / variables / evaluate

Sessions

A debug session corresponds to one running adapter. Multiple sessions can run simultaneously per project (e.g. server + client). Each session has its own threads, stack frames, breakpoints, and variables tree.

Configuration

Debug configurations live in tasks.json / debug.json per project, similar to VS Code's launch.json. The schema is defined in crates/dap_adapters and validated at parse time.

Inline UI

Beyond the dedicated panel, the editor itself shows:

• Breakpoint markers in the gutter (with conditional/log breakpoints).
• Inline values (e.g. x = 42) at the cursor's current frame.
• Stack-frame highlight on the active line.

Adapter installation

DAP adapters are installed similarly to LSP servers — the adapter wrapper knows how to fetch and validate the binary. Many use the Node runtime; some use system binaries (lldb, delve, dlv, js-debug).

Integration points

• Below: crates/dap for transport, crates/dap_adapters for adapter registration.
• Above: crates/debugger_ui panels and the editor's gutter integration.
• Tests: crates/debugger_tools provides fakes and a DAP message inspector.

Entry points for modification

• New adapter — crates/dap_adapters/src/<adapter>.rs. Or ship as an extension via crates/debug_adapter_extension.
• New panel — crates/debugger_ui/src/.
• DAP transport bug — crates/dap/src/lsp.rs (the file is named after LSP for historical reasons; DAP and LSP share JSON-RPC framing).

Related pages

• Debugger — user-facing flow
• Project — owner of DebuggerStore
• LSP — sibling protocol with similar architecture