Home >Backend Development >Golang >Mastering Golang Debugging in Emacs
Since I've started developing in Golang I didn't really use the debugger. Instead I was naively adding fmt.Print statements everywhere to validate my code ?. While print statements and logs might be also your first debugging instinct, they often fall short when dealing with large and complex code base, with sophisticated runtime behaviour and (of course!) complex concurrency issues that seem impossible to reproduce.
After starting working on more complex projects (like this one: https://github.com/cloudoperators/heureka) I had to force myself to have a deeper look at delve (the Golang debugger) and see what Emacs offers for interacting with it. While the Go ecosystem offers excellent debugging tools, integrating them into a comfortable development workflow can be challenging.
In this post I'll elaborate the powerful combination of Emacs, Delve, and dape. Together, these tools create a debugging experience that mimics (and often surpasses) traditional IDEs, while preserving the flexibility and extensibility that Emacs is famous for.
This is what you can expect:
In this post I assume you already have some Emacs experience and now how to configure packages and write small Elisp snippets. I personally use straight.el as a package manager, minimal-emacs.d as a minimal vanilla Emacs configuration (along with my own custommizations), dape as the debug adapter client and eglot as my LSP client.
For Emacs 29 users, eglot is built-in. Check out configuring eglot for gopls and some more advanced gopls settings. We'll first add dape:
(use-package dape :straight t :config ;; Pulse source line (performance hit) (add-hook 'dape-display-source-hook 'pulse-momentary-highlight-one-line) ;; To not display info and/or buffers on startup ;; (remove-hook 'dape-start-hook 'dape-info) (remove-hook 'dape-start-hook 'dape-repl))
And go-mode:
(use-package go-mode :straight t :mode "\.go\'" :hook ((before-save . gofmt-before-save)) :bind (:map go-mode-map ("M-?" . godoc-at-point) ("M-." . xref-find-definitions) ("M-_" . xref-find-references) ;; ("M-*" . pop-tag-mark) ;; Jump back after godef-jump ("C-c m r" . go-run)) :custom (gofmt-command "goimports"))
Install Delve and gopls, the LSP server:
# Install Delve go install github.com/go-delve/delve/cmd/dlv@latest # Install gopls go install golang.org/x/tools/gopls@latest
Additionally I have a bunch of other tools which I use from time to time:
go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest go install github.com/onsi/ginkgo/v2/ginkgo@latest go install -v golang.org/x/tools/cmd/godoc@latest go install -v golang.org/x/tools/cmd/goimports@latest go install -v github.com/stamblerre/gocode@latest go install -v golang.org/x/tools/cmd/gorename@latest go install -v golang.org/x/tools/cmd/guru@latest go install -v github.com/cweill/gotests/...@latest go install -v github.com/davidrjenni/reftools/cmd/fillstruct@latest go install -v github.com/fatih/gomodifytags@latest go install -v github.com/godoctor/godoctor@latest go install -v github.com/haya14busa/gopkgs/cmd/gopkgs@latest go install -v github.com/josharian/impl@latest go install -v github.com/rogpeppe/godef@latest
Then you need to configure the corresponding Emacs packages:
(use-package ginkgo :straight (:type git :host github :repo "garslo/ginkgo-mode") :init (setq ginkgo-use-pwd-as-test-dir t ginkgo-use-default-keys t)) (use-package gotest :straight t :after go-mode :bind (:map go-mode-map ("C-c t f" . go-test-current-file) ("C-c t t" . go-test-current-test) ("C-c t j" . go-test-current-project) ("C-c t b" . go-test-current-benchmark) ("C-c t c" . go-test-current-coverage) ("C-c t x" . go-run))) (use-package go-guru :straight t :hook (go-mode . go-guru-hl-identifier-mode)) (use-package go-projectile :straight t :after (projectile go-mode)) (use-package flycheck-golangci-lint :straight t :hook (go-mode . flycheck-golangci-lint-setup)) (use-package go-eldoc :straight t :hook (go-mode . go-eldoc-setup)) (use-package go-tag :straight t :bind (:map go-mode-map ("C-c t a" . go-tag-add) ("C-c t r" . go-tag-remove)) :init (setq go-tag-args (list "-transform" "camelcase"))) (use-package go-fill-struct :straight t) (use-package go-impl :straight t) (use-package go-playground :straight t)
There is no particular reason why I use dape instead of dap. When I was still using MinEmacs it was part of it and I just got used to it. As the documentation states:
- 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.
- 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.
If you ever worked with VSCode you already know that it uses a launch.json to store different debugging profiles:
(use-package dape :straight t :config ;; Pulse source line (performance hit) (add-hook 'dape-display-source-hook 'pulse-momentary-highlight-one-line) ;; To not display info and/or buffers on startup ;; (remove-hook 'dape-start-hook 'dape-info) (remove-hook 'dape-start-hook 'dape-repl))
You have different fields/properties which according to this page you can tweak in your debugging configuration:
Property | Description |
---|---|
name | Name for your configuration that appears in the drop down in the Debug viewlet |
type | Always set to "go". This is used by VS Code to figure out which extension should be used for debugging your code |
request | Either of launch or attach. Use attach when you want to attach to an already running process |
mode | For launch requests, either of auto, debug, remote, test, exec. For attach requests, use either local or remote |
program | Absolute path to the package or file to debug when in debug & test mode, or to the pre-built binary file to debug in exec mode |
env | Environment variables to use when debugging. Example: { "ENVNAME": "ENVVALUE" } |
envFile | Absolute path to a file containing environment variable definitions |
args | Array of command line arguments that will be passed to the program being debugged |
showLog | Boolean indicating if logs from delve should be printed in the debug console |
logOutput | Comma separated list of delve components for debug output |
buildFlags | Build flags to be passed to the Go compiler |
remotePath | Absolute path to the file being debugged on the remote machine |
processId | ID of the process that needs debugging (for attach request with local mode) |
Now let's put our knowledge into practice by debugging a real application implementing a REST API.
Our example is a REST API for task management with the following structure:
(use-package dape :straight t :config ;; Pulse source line (performance hit) (add-hook 'dape-display-source-hook 'pulse-momentary-highlight-one-line) ;; To not display info and/or buffers on startup ;; (remove-hook 'dape-start-hook 'dape-info) (remove-hook 'dape-start-hook 'dape-repl))
Let's have a look at the core components.
The Task represents our core domain model:
(use-package go-mode :straight t :mode "\.go\'" :hook ((before-save . gofmt-before-save)) :bind (:map go-mode-map ("M-?" . godoc-at-point) ("M-." . xref-find-definitions) ("M-_" . xref-find-references) ;; ("M-*" . pop-tag-mark) ;; Jump back after godef-jump ("C-c m r" . go-run)) :custom (gofmt-command "goimports"))
The TaskStore handles our in-memory data operations:
# Install Delve go install github.com/go-delve/delve/cmd/dlv@latest # Install gopls go install golang.org/x/tools/gopls@latest
The API exposes following endpoints:
go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest go install github.com/onsi/ginkgo/v2/ginkgo@latest go install -v golang.org/x/tools/cmd/godoc@latest go install -v golang.org/x/tools/cmd/goimports@latest go install -v github.com/stamblerre/gocode@latest go install -v golang.org/x/tools/cmd/gorename@latest go install -v golang.org/x/tools/cmd/guru@latest go install -v github.com/cweill/gotests/...@latest go install -v github.com/davidrjenni/reftools/cmd/fillstruct@latest go install -v github.com/fatih/gomodifytags@latest go install -v github.com/godoctor/godoctor@latest go install -v github.com/haya14busa/gopkgs/cmd/gopkgs@latest go install -v github.com/josharian/impl@latest go install -v github.com/rogpeppe/godef@latest
Here's the server implementation:
(use-package ginkgo :straight (:type git :host github :repo "garslo/ginkgo-mode") :init (setq ginkgo-use-pwd-as-test-dir t ginkgo-use-default-keys t)) (use-package gotest :straight t :after go-mode :bind (:map go-mode-map ("C-c t f" . go-test-current-file) ("C-c t t" . go-test-current-test) ("C-c t j" . go-test-current-project) ("C-c t b" . go-test-current-benchmark) ("C-c t c" . go-test-current-coverage) ("C-c t x" . go-run))) (use-package go-guru :straight t :hook (go-mode . go-guru-hl-identifier-mode)) (use-package go-projectile :straight t :after (projectile go-mode)) (use-package flycheck-golangci-lint :straight t :hook (go-mode . flycheck-golangci-lint-setup)) (use-package go-eldoc :straight t :hook (go-mode . go-eldoc-setup)) (use-package go-tag :straight t :bind (:map go-mode-map ("C-c t a" . go-tag-add) ("C-c t r" . go-tag-remove)) :init (setq go-tag-args (list "-transform" "camelcase"))) (use-package go-fill-struct :straight t) (use-package go-impl :straight t) (use-package go-playground :straight t)
Let's look at our main function:
{ "name": "Launch file", "type": "go", "request": "launch", "mode": "auto", "program": "${file}" }
Let's start the server:
taskapi/ ├── go.mod ├── go.sum ├── main.go ├── task_store.go └── task_test.go
Now from a different terminal create a new task:
import ( "fmt" ) type Task struct { ID int `json:"id"` Title string `json:"title"` Description string `json:"description"` Done bool `json:"done"` }
Response:
type TaskStore struct { tasks map[int]Task nextID int } func NewTaskStore() *TaskStore { return &TaskStore{ tasks: make(map[int]Task), nextID: 1, } }
Let's see if we can fetch it:
// CreateTask stores a given Task internally func (ts *TaskStore) CreateTask(task Task) Task { task.ID = ts.nextID ts.tasks[task.ID] = task ts.nextID++ return task } // GetTask retrieves a Task by ID func (ts *TaskStore) GetTask(id int) (Task, error) { task, exists := ts.tasks[id] if !exists { return Task{}, fmt.Errorf("task with id %d not found", id) } return task, nil } // UpdateTask updates task ID with a new Task object func (ts *TaskStore) UpdateTask(id int, task Task) error { if _, exists := ts.tasks[id]; !exists { return fmt.Errorf("task with id %d not found", id) } task.ID = id ts.tasks[id] = task return nil }
Response:
package main import ( "encoding/json" "fmt" "net/http" ) // Server implements a web application for managing tasks type Server struct { store *TaskStore } func (s *Server) handleCreateTask(w http.ResponseWriter, r *http.Request) { if r.Method != http.MethodPost { http.Error(w, "Method not allowed", http.StatusMethodNotAllowed) return } var task Task if err := json.NewDecoder(r.Body).Decode(&task); err != nil { http.Error(w, err.Error(), http.StatusBadRequest) return } createdTask := s.store.CreateTask(task) w.Header().Set("Content-Type", "application/json") json.NewEncoder(w).Encode(createdTask) } func (s *Server) handleGetTask(w http.ResponseWriter, r *http.Request) { if r.Method != http.MethodGet { http.Error(w, "Method not allowed", http.StatusMethodNotAllowed) return } id := 0 fmt.Sscanf(r.URL.Query().Get("id"), "%d", &id) task, err := s.store.GetTask(id) if err != nil { http.Error(w, err.Error(), http.StatusNotFound) return } w.Header().Set("Content-Type", "application/json") json.NewEncoder(w).Encode(task) }
Below are some unit tests (written in Ginkgo) for the TaskStore:
package main import ( "log" "net/http" ) func main() { store := NewTaskStore() server := &Server{store: store} http.HandleFunc("/task/create", server.handleCreateTask) http.HandleFunc("/task/get", server.handleGetTask) log.Printf("Starting server on :8080") log.Fatal(http.ListenAndServe(":8080", nil)) }
go build -o taskapi *.go ./taskapi 2024/11/14 07:03:48 Starting server on :8080
In Emacs I would then call ginkgo-run-this-container as shown in this screenshot:
In order to debug our Task API we have following approaches:
Here are the options for different request types:
request | mode | required | optional | ||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
debug | program | dlvCwd, env, backend, args, cwd, buildFlags, output, noDebug | ||||||||||||||||||||||||||||||||
test | program | dlvCwd, env, backend, args, cwd, buildFlags, output, noDebug | |||||||||||||||||||||||||||||||||
exec | program | dlvCwd, env, backend, args, cwd, noDebug | |||||||||||||||||||||||||||||||||
core | program, corefilePath | dlvCwd, env | |||||||||||||||||||||||||||||||||
replay | traceDirPath | dlvCwd, env | |||||||||||||||||||||||||||||||||
attach | local | processId | backend | ||||||||||||||||||||||||||||||||
remote |
Here's our first debugging profile for .dir-locals.el:
(use-package dape :straight t :config ;; Pulse source line (performance hit) (add-hook 'dape-display-source-hook 'pulse-momentary-highlight-one-line) ;; To not display info and/or buffers on startup ;; (remove-hook 'dape-start-hook 'dape-info) (remove-hook 'dape-start-hook 'dape-repl))
? You may want to use a different value for command-cwd. In my case I wanted to start the debugger in a directory which currently is not a project. default-directory is a variable which holds the working directory for the current buffer you're currently in.
Start debugging:
After starting the debugger with this profile, you should see in the dape-repl buffer:
(use-package go-mode :straight t :mode "\.go\'" :hook ((before-save . gofmt-before-save)) :bind (:map go-mode-map ("M-?" . godoc-at-point) ("M-." . xref-find-definitions) ("M-_" . xref-find-references) ;; ("M-*" . pop-tag-mark) ;; Jump back after godef-jump ("C-c m r" . go-run)) :custom (gofmt-command "goimports"))
Note that we didn't specify any binary/file to debug (we had :program "." in .dir-locals.el). delve will automatically build the binary before it launches the application:
# Install Delve go install github.com/go-delve/delve/cmd/dlv@latest # Install gopls go install golang.org/x/tools/gopls@latest
Let's add a profile for connecting to an existing debugging session:
go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest go install github.com/onsi/ginkgo/v2/ginkgo@latest go install -v golang.org/x/tools/cmd/godoc@latest go install -v golang.org/x/tools/cmd/goimports@latest go install -v github.com/stamblerre/gocode@latest go install -v golang.org/x/tools/cmd/gorename@latest go install -v golang.org/x/tools/cmd/guru@latest go install -v github.com/cweill/gotests/...@latest go install -v github.com/davidrjenni/reftools/cmd/fillstruct@latest go install -v github.com/fatih/gomodifytags@latest go install -v github.com/godoctor/godoctor@latest go install -v github.com/haya14busa/gopkgs/cmd/gopkgs@latest go install -v github.com/josharian/impl@latest go install -v github.com/rogpeppe/godef@latest
Now let's start the debugger on the CLI:
(use-package ginkgo :straight (:type git :host github :repo "garslo/ginkgo-mode") :init (setq ginkgo-use-pwd-as-test-dir t ginkgo-use-default-keys t)) (use-package gotest :straight t :after go-mode :bind (:map go-mode-map ("C-c t f" . go-test-current-file) ("C-c t t" . go-test-current-test) ("C-c t j" . go-test-current-project) ("C-c t b" . go-test-current-benchmark) ("C-c t c" . go-test-current-coverage) ("C-c t x" . go-run))) (use-package go-guru :straight t :hook (go-mode . go-guru-hl-identifier-mode)) (use-package go-projectile :straight t :after (projectile go-mode)) (use-package flycheck-golangci-lint :straight t :hook (go-mode . flycheck-golangci-lint-setup)) (use-package go-eldoc :straight t :hook (go-mode . go-eldoc-setup)) (use-package go-tag :straight t :bind (:map go-mode-map ("C-c t a" . go-tag-add) ("C-c t r" . go-tag-remove)) :init (setq go-tag-args (list "-transform" "camelcase"))) (use-package go-fill-struct :straight t) (use-package go-impl :straight t) (use-package go-playground :straight t)
Now within Emacs you can launch dape and select the go-attach-taskapi profile:
In this scenario the application is already running but you want to attach the debugger to it. First launch the application:
{ "name": "Launch file", "type": "go", "request": "launch", "mode": "auto", "program": "${file}" }
Find out its process ID (PID):
taskapi/ ├── go.mod ├── go.sum ├── main.go ├── task_store.go └── task_test.go
Let's add another debug profile:
import ( "fmt" ) type Task struct { ID int `json:"id"` Title string `json:"title"` Description string `json:"description"` Done bool `json:"done"` }
We'll need a helper function:
type TaskStore struct { tasks map[int]Task nextID int } func NewTaskStore() *TaskStore { return &TaskStore{ tasks: make(map[int]Task), nextID: 1, } }
Now I start the debugger:
If I now send a POST request like this one:
// CreateTask stores a given Task internally func (ts *TaskStore) CreateTask(task Task) Task { task.ID = ts.nextID ts.tasks[task.ID] = task ts.nextID++ return task } // GetTask retrieves a Task by ID func (ts *TaskStore) GetTask(id int) (Task, error) { task, exists := ts.tasks[id] if !exists { return Task{}, fmt.Errorf("task with id %d not found", id) } return task, nil } // UpdateTask updates task ID with a new Task object func (ts *TaskStore) UpdateTask(id int, task Task) error { if _, exists := ts.tasks[id]; !exists { return fmt.Errorf("task with id %d not found", id) } task.ID = id ts.tasks[id] = task return nil }
The debugger should automatically halt at the set breakpoint:
Being able to debug tests in Golang is crucial. For running ginkgo tests I use ginkgo-mode which has several features:
And as an output I get:
(use-package dape :straight t :config ;; Pulse source line (performance hit) (add-hook 'dape-display-source-hook 'pulse-momentary-highlight-one-line) ;; To not display info and/or buffers on startup ;; (remove-hook 'dape-start-hook 'dape-info) (remove-hook 'dape-start-hook 'dape-repl))
This is the basic configuration for debugging Ginkgo tests:
(use-package go-mode :straight t :mode "\.go\'" :hook ((before-save . gofmt-before-save)) :bind (:map go-mode-map ("M-?" . godoc-at-point) ("M-." . xref-find-definitions) ("M-_" . xref-find-references) ;; ("M-*" . pop-tag-mark) ;; Jump back after godef-jump ("C-c m r" . go-run)) :custom (gofmt-command "goimports"))
If I chose the go-test-ginkgo debug profile I should be able to debug the tests:
Now the configuration is quite static and therefore you cannot preselect the unit test / container. We need to somehow make the parameter -ginkgo.focus dynamic:
# Install Delve go install github.com/go-delve/delve/cmd/dlv@latest # Install gopls go install golang.org/x/tools/gopls@latest
Afterwards If I have a look at the dape-configs variable I should see this value:
go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest go install github.com/onsi/ginkgo/v2/ginkgo@latest go install -v golang.org/x/tools/cmd/godoc@latest go install -v golang.org/x/tools/cmd/goimports@latest go install -v github.com/stamblerre/gocode@latest go install -v golang.org/x/tools/cmd/gorename@latest go install -v golang.org/x/tools/cmd/guru@latest go install -v github.com/cweill/gotests/...@latest go install -v github.com/davidrjenni/reftools/cmd/fillstruct@latest go install -v github.com/fatih/gomodifytags@latest go install -v github.com/godoctor/godoctor@latest go install -v github.com/haya14busa/gopkgs/cmd/gopkgs@latest go install -v github.com/josharian/impl@latest go install -v github.com/rogpeppe/godef@latest
After starting the debugger (with the debug-focused-test profile) in the dape-repl buffer I get:
(use-package ginkgo :straight (:type git :host github :repo "garslo/ginkgo-mode") :init (setq ginkgo-use-pwd-as-test-dir t ginkgo-use-default-keys t)) (use-package gotest :straight t :after go-mode :bind (:map go-mode-map ("C-c t f" . go-test-current-file) ("C-c t t" . go-test-current-test) ("C-c t j" . go-test-current-project) ("C-c t b" . go-test-current-benchmark) ("C-c t c" . go-test-current-coverage) ("C-c t x" . go-run))) (use-package go-guru :straight t :hook (go-mode . go-guru-hl-identifier-mode)) (use-package go-projectile :straight t :after (projectile go-mode)) (use-package flycheck-golangci-lint :straight t :hook (go-mode . flycheck-golangci-lint-setup)) (use-package go-eldoc :straight t :hook (go-mode . go-eldoc-setup)) (use-package go-tag :straight t :bind (:map go-mode-map ("C-c t a" . go-tag-add) ("C-c t r" . go-tag-remove)) :init (setq go-tag-args (list "-transform" "camelcase"))) (use-package go-fill-struct :straight t) (use-package go-impl :straight t) (use-package go-playground :straight t)
?Notice that just "1 of 5 specs" (❶) were ran, meaning that ginkgo only focussed on the container we have specified (❷).
Throughout my debugging experience, I have come to appreciate several best practices:
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