Dape - Debug Adapter Protocol for Emacs

Dape is a debug adapter client for Emacs. The debug adapter protocol, much like its more well-known counterpart, the language server protocol, aims to establish a common API for programming tools. However, instead of functionalities such as code completions, it provides a standardized interface for debuggers.

To begin a debugging session, invoke the dape command. In the minibuffer prompt, enter a debug adapter configuration name from dape-configs.

For complete functionality, make sure to enable eldoc-mode in your source buffers and repeat-mode for more pleasant key mappings.

Features

• Batteries included support (describe-variable dape-configs)
• Log breakpoints
• Conditional breakpoints
• Variable explorer
• Variable watch
• Variable hover with eldoc
• REPL
• gdb-mi.el like interface
• Memory editor with hexl
• Integration with compile
• Debug adapter configuration ergonomics
• No external dependencies outside of core Emacs

With (setq dape-buffer-window-arrangement 'right): And with (setq dape-buffer-window-arrangement 'gud) + corfu as completion-in-region-function: With Minibuffer adapter configuration hints:

Screenshots taken with modus-operandi-tinted.

Configuration

Dape includes pre-defined debug adapter configurations for various programming languages. Refer to dape-configs for more details. If dape doesn’t include a configuration suitable for your needs, you can implement your own.

(use-package dape
  :preface
  ;; By default dape shares the same keybinding prefix as `gud'
  ;; If you do not want to use any prefix, set it to nil.
  ;; (setq dape-key-prefix "\C-x\C-a")

  :hook
  ;; Save breakpoints on quit
  ;; ((kill-emacs . dape-breakpoint-save)
  ;; Load breakpoints on startup
  ;;  (after-init . dape-breakpoint-load))

  :init
  ;; To use window configuration like gud (gdb-mi)
  ;; (setq dape-buffer-window-arrangement 'gud)

  :config
  ;; Info buffers to the right
  ;; (setq dape-buffer-window-arrangement 'right)

  ;; Global bindings for setting breakpoints with mouse
  ;; (dape-breakpoint-global-mode)

  ;; To not display info and/or buffers on startup
  ;; (remove-hook 'dape-on-start-hooks 'dape-info)
  ;; (remove-hook 'dape-on-start-hooks 'dape-repl)

  ;; To display info and/or repl buffers on stopped
  ;; (add-hook 'dape-on-stopped-hooks 'dape-info)
  ;; (add-hook 'dape-on-stopped-hooks 'dape-repl)

  ;; Kill compile buffer on build success
  ;; (add-hook 'dape-compile-compile-hooks 'kill-buffer)

  ;; Save buffers on startup, useful for interpreted languages
  ;; (add-hook 'dape-on-start-hooks (lambda () (save-some-buffers t t)))

  ;; Projectile users
  ;; (setq dape-cwd-fn 'projectile-project-root)
  )

Differences with dap-mode

Dape has no dependencies outside of core Emacs packages, and tries to use get as much out of them possible.

Dape takes a slightly different approach to configuration.

• Dape does not support launch.json files, if per project configuration is needed use dir-locals and dape-command.
• Dape enhances ergonomics within the minibuffer by allowing users to modify or add PLIST entries to an existing configuration using options. For example dape-config :cwd default-directory :program ＂/home/user/b.out＂ compile ＂gcc -g -o b.out main.c＂.
• No magic, no special variables like ${workspaceFolder}. Instead, functions and variables are resolved before starting a new session.
• Tries to envision how debug adapter configurations would be implemented in Emacs if vscode never existed.

Supported debug adapters

In theory all debug adapters should be compatible with Dape.

Javascript - vscode-js-*

1. Install node
2. Visit https://github.com/microsoft/vscode-js-debug/releases/ and download the asset js-debug-dap-<version>.tar.gz
3. Unpack mkdir -p ~/.emacs.d/debug-adapters && tar -xvzf js-debug-dap-<version>.tar.gz -C ~/.emacs.d/debug-adapters

For more information see OPTIONS.md.

Go - dlv

See delve installation. For more information see documentation.

C, C++, Rust, and more - GDB

Ensure that your GDB version is 14.1 or newer. For further details, consult the documentation.

C, C++ and Rust - codelldb

1. Download latest vsix release for your platform codelldb-<platform>-<os>.vsix
2. Unpack mkdir -p ~/.emacs.d/debug-adapters && unzip codelldb-<platform>-<os>.vsix -d ~/.emacs.d/debug-adapters/codelldb

See manual for more information.

C and C++ - cpptools

Download latesnd unpack vsix file with your favorite unzipper.

1. Download latest vsix release for your platform cpptools-<platform>-<os>.vsix
2. Unpack mkdir -p ~/.emacs.d/debug-adapters && unzip cpptools-<os>-<platform>.vsix -d ~/.emacs.d/debug-adapters/cpptools
3. Then chmod +x ~/.emacs.d/debug-adapters/cpptools/extension/debugAdapters/bin/OpenDebugAD7
4. And chmod +x ~/.emacs.d/debug-adapters/cpptools/extension/debugAdapters/lldb-mi/bin/lldb-mi

See options.

Python - debugpy

Install debugpy with pip pip install debugpy

See options.

Godot

Configure debug adapter port under “Editor” > “Editor Settings” > “Debug Adapter”.

Dart - flutter

See for installation https://docs.flutter.dev/get-started/install

C# - netcoredbg

See https://github.com/Samsung/netcoredbg for installation

Ruby - rdbg

Install with gem install debug.

See https://github.com/ruby/debug for more information

Java - JDTLS with Java Debug Server plugin

See https://github.com/eclipse-jdtls/eclipse.jdt.ls for installation of JDTLS. See https://github.com/microsoft/java-debug for installation of the Java Debug Server plugin. The Java config depends on Eglot running JDTLS with the plugin prior to starting Dape. Extend eglot-server-programs as follows to have JDTLS load the plugin:

(add-to-list 'eglot-server-programs
             `((java-mode java-ts-mode) .
               ("jdtls"
                :initializationOptions
                (:bundles ["/PATH/TO/java-debug/com.microsoft.java.debug.plugin/target/com.microsoft.java.debug.plugin-VERSION.jar"]))))

Other untested adapters

If you find a working configuration for any other debug adapter please submit a PR.

See microsofts list for other adapters, your mileage will vary.

Contribute

dape is subject to the same copyright assignment policy as GNU Emacs.

Any legally significant contributions can only be merged after the author has completed their paperwork. See Contributor’s Frequently Asked Questions (FAQ) for more information.

Performance

Some minor gains to performance in the debugger can be achieved in changing Emacs configuration values for process interaction and garbage collection.

gc-cons-threshold

This variable controls the frequency of garbage collection in Emacs. Too high a value will lead to increased system memory pressure and longer stalls, and too low a value will result in extra interruptions and context switches (poor performance).

According to GNU Emacs Maintainer Eli Zaretskii:

My suggestion is to repeatedly multiply gc-cons-threshold by 2 until you stop seeing significant improvements in
responsiveness, and in any case not to increase by a factor larger than 100 or somesuch. If even a 100-fold increase
doesn't help, there's some deeper problem with the Lisp code which produces so much garbage, or maybe GC is not the
reason for slowdown.

Abiding the upper end of that advice, you can try to set gc-cons-threshold to 100x the original value:

(setq gc-cons-threshold 80000000) ;; original value * 100

read-process-output-max

The default read-process-output-max of 4096 bytes may inhibit performance to some degree, also.

Linux

On Linux, you should be able to set it up to about 1mb. To check the max value, check the output of:

cat /proc/sys/fs/pipe-max-size

To set it:

(setq read-process-output-max (* 1024 1024)) ;; 1mb

Mac OS

For Mac OS, there isn’t an easy way to see the operating system pipe-max-size. It’s probably about 64kb.

(setq read-process-output-max (* 64 1024)) ;; 64k

Windows

There doesn’t seem to be a limit for Windows. You can try 1mb.

(setq read-process-output-max (* 1024 1024)) ;; 1mb

Bugs and issues

Before reporting any issues (setq dape-debug t) and take a look at *dape-repl* buffer. Please share your *dape-repl* and *dape-connection events* in the buffer contents with the bug report. The master branch is used as an development branch and releases on elpa should be more stable so in the mean time use elpa if the bug is a breaking you workflow.

Acknowledgements

Big thanks to João Távora for the input and jsonrpc; the project wouldn’t be where it is without João.