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Debugging

The Go extension allows you to launch or attach to Go programs for debugging. You can inspect variables and stacks, set breakpoints, and do other debugging activities using VS Code’s Debugging UI.

These debugging features are possible by using Delve, the Go debugger. The Go extension has been communicating with Delve through a custom debug adapter program (legacy mode). As the new Delve's native debug adapter implementation has become available (since Delve v1.6.1), the Go extension is transitioning to deprecate the legacy debug adapter in favor of direct communication with Delve via DAP.

📣 We are happy to announce that the new dlv-dap mode of Delve integration is enabled for local debugging by default. For remote debugging it is the default in Go Nightly and is available with stable builds on demand with "debugAdapter": "dlv-dap" attribute in launch.json or settings.json!

Many features and settings described in this document may be available only with the new dlv-dap mode. For troubleshooting and configuring the legacy debug adapter, see the legacy debug adapter documentation.

Getting Started

Open a file to debug (either package main source file or the test file) in the editor, and select the Run and Debug button from the Run view. Alternatively, you can start debugging using Start Debugging (F5) command from the Run menu or from the Command Palette (Linux/Windows: Ctrl+Shift+P, Mac: ⇧+⌘+P).

When no configuration is configured yet (no .vscode/launch.json file), the extension will choose a default configuration based on the file open in the editor.

If you already have launch configurations for the project (.vscode/launch.json), the Run view will display the configuration list to choose from.

Delve Install
❗ When you start debugging for the first time or if the `dlv` executable on your system is too old to support DAP, the extension may ask to install or update Delve. Please follow the instructions to install, and then start the debugging session again (i.e. selecting the source file, pressing F5 or click the codelens).

Watch "Go: Writing and debugging fast, reliable, and efficient software" to learn more about debugging features.

Please review the Features section that provides an overview of the debug UI and available features.

Staying Up-To-Date

Delve’s native DAP implementation is under active development, so take advantage of the most recent features and bug fixes by installing the latest version of Delve.

The easiest way to update dlv on demand is to use the "Go: Install/Update Tools" command from the Command Palette (Linux/Windows: Ctrl+Shift+P, Mac: ⇧+⌘+P). The command will show dlv in the tool list.

Once dlv is installed on your system, the extension will prompt you for update whenever installing a newer version is necessary (usually after the Go extension upgrade). You can set the go.toolsManagement.autoUpdate setting so the extension can update dlv automatically for you.

If you need to install dlv manually outside of VS Code (for example, you are building a dev container with necessary tools preinstalled, or install dlv built from the tree head), follow the instruction in Manually installing dlv.

💡 The extension used to install a dev version of dlv as a separate binary (known as dlv-dap). As Delve DAP is stable and the transition work is near completion, from v0.31.0 (to be released in Jan 2022), the extension will switch to use dlv, instead of the dlv-dap binary. It is safe to delete dlv-dap installed on the system after v0.31.0 release.

Switching to legacy debug adapter

If you need to use the legacy debug adapter (legacy mode) by default, add the following in your VSCode settings.

Note that the extension still uses the legacy debug adapter for remote debugging.

    "go.delveConfig": {
        "debugAdapter": "legacy",
    }

If you want to switch to legacy for only a subset of your launch configurations, you can use the debugAdapter attribute to switch between "dlv-dap" and "legacy" mode.

If you chose to switch to legacy because of bugs or limitations in the new debug adapter, please open an issue to help us improve the new debug adapter.

Features

For general debugging features such as inspecting variables, setting breakpoints, and other activities that aren't language-dependent, review VS Code debugging.

Configure

When you need more than the default debugging setup, you can create a launch configuration file for the project by clicking the "create a launch.json file" link in the Run view. Then, choose from the debug configuration drop-down menu. VS Code will create a launch.json file in a .vscode folder in your workspace (project root folder) or in your user settings or workspace settings.

If you already have a launch.json for your project, you can open it using Open launch.json.

To add a new configuration to an existing launch.json, choose the "Add Configuration…" button to invoke the snippet IntelliSense.

Create launch.json

There are many configuration attributes (see the Launch.json attributes section). IntelliSense in VS Code’s launch.json editor will help you navigate available options and documentation.

Launch

You can choose "Start Debugging (F5)" and "Run Without Debugging (^F5)" a.k.a the noDebug mode. This feature uses a launch request type configuration. Its program attribute needs to be either the go file or folder of the main package or test file. In this mode, the Go extension will start the debug session by building and launching the program. The launched program will be terminated when the debug session ends.

  • Supported modes
    • debug: build and debug a main package
    • test: build and debug a test
    • exec: debug a precompiled binary
      • The binary must be built with go build -gcflags=all="-N -l" to disable inlining and optimizations that can interfere with debugging.
    • auto: automatically choose between debug and test depending on the open file

⚠️ If a port attribute is added to any of the launch configurations, it will signal VS Code that instead of launching the debug server internally, it should connect to an external user-specified dlv dap server at host:port and launch the target there. See "Remote Debugging" for more details).

The program attribute must point to the absolute path to the package or binary to debug in the remote host’s file system even when substitutePath is specified.

Attach

You can use this configuration to attach to a running process or a running debug session.

  • Supported modes
    • local: attaches to a local process
      • The binary must be built with go build -gcflags=all="-N -l" to disable inlining and optimizations that can interfere with debugging.
    • remote: attaches to an in-progress debug session run by an external server

You can debug an already running program using the local mode type configuration. The Go extension will start dlv dap and configure it to attach to the specified process. Users can select the process to debug with one of the following options:

  • Specifying the numeric process id (PID) with the processId attribute.
  • Specifying the target program name in the processId attribute. If there are multiple processes matching the specified program name, the extension will show the list of matching processes at the start of the debug session.
  • Specifying 0 in the processId attribute and selecting the process from the drop-down menu at the start of the debug session.

Attach to a running process

NOTE: If a port attribute is added to a local attach configuration, it will signal VS Code that instead of launching the debug server internally, it should connect to an external user-specified dlv dap server at host:port and attach to the target there. The process resolution features will only work if localhost is used. See "Remote Debugging" for more details).

You can connect to an already running remote debug session using the remote mode. Specify optional host and required port for the external dlv --headless server that already took program or process id details as command-line arguments. See "Remote Debugging" for more details).

When you end an attach debug session, the debug UI allows you to choose to:

  • [DEFAULT] Disconnect: disconnect the client and
    • local: leave the target process running (dlv terminates).
    • remote: let dlv decide if it can continue running (--accept-multiclient mode only); if so, the target will stay in halted or running state it was in at disconnect.
      • dlv debug/test/exec: terminate the target process if dlv terminates.
      • dlv attach: leave the target process running even if dlv terminates.
  • Stop: stop the attached server and the target process.

Terminate Debugging started with Attach

Debug Actions

Once a debug session starts, the Debug toolbar will appear on the top of the editor.

Debug Tool Bar

  • Continue / Pause F5
  • Step Over (aka next in Delve) F10
  • Step Into (aka step in Delve) F11
  • Step Out (aka stepout in Delve) Shift+F11 or ⇧F11
  • Restart (currently this is "Stop + Start") Ctrl+Shift+F5 or ⇧⌘F5
  • Stop (terminate the debugee. Available in Launch request) Shift+F5 or ⇧F5
  • Disconnect (detach from the debugee. Available only in Attach request) Shift+F5 or ⇧F5
  • Terminate (terminate the debugee. Available only in Attach request) Alt+Shift+F5 or ⌥⇧F5

Breakpoints

See VS Code’s Debug Documentation on Breakpoints to get familiar with VS Code’s UI. The Go debugger supports multiple ways to configure breakpoints.

  • Breakpoints: you can set breakpoints by clicking on the editor margin or using F9 on the current line. If the breakpoints can’t be set by Delve, VS Code will show the failure reason and grey out the dot.

Invalid breakpoint

  • Conditional breakpoints: you can specify breakpoint conditions (similar to Delve’s condition command).
    • Expression condition: takes a boolean expression.
    • Hit count: supports comparison operators (>, >=, <, <=, ==, !=) with an integer value. % n form means we should stop at the breakpoint when the hitcount is a multiple of n.

Conditional Breakpoint

  • Function Breakpoints: breakpoints can be set based on function names. Press the + button in the BREAKPOINTS section header and enter the location in the form of <function>[:<line>]. This sets the breakpoint in the line inside the function. The full syntax for function is <package>.(*<receiver type>).<function_name> as specified in Delve’s location spec. Function breakpoints are shown with a red triangle in the BREAKPOINTS section.

Function breakpoint

  • Logpoints: a logpoint is a variant of breakpoint that does not 'break', but instead logs a message to DEBUG CONSOLE and continues execution. Expressions within {} are interpolated. For the list of acceptable expressions and syntax, see Delve's documentation.

Data Inspection

You can inspect variables in the VARIABLES section of the Run view or by hovering over their source in the editor. Variable values and expression evaluation are relative to the selected stack frame in the CALL section.

By default, the VARIABLES section hides global variables, and shows only local variables and function arguments. However, you can still inspect global variables from the DEBUG CONSOLE panel. If you prefer to have the VARIABLES section show global variables, set the showGlobalVariables attribute in the launch.json configuration, or set it in the go.delveConfig setting.

When you select a variable and right click from the VARIABLES section, the context menu will present shortcuts to features such as:

  • Set Value: you can set/modify simple string, numeric, pointer values. Using composite literals, or memory allocation is not supported.
  • Copy Value: this copies the value in clipboard.
  • Copy as Expression: this is useful when you need to query from the REPL in the DEBUG CONSOLE panel.
  • Add to Watch: this will automatically add the expression to the WATCH section.

Shadowed variables will be marked with ().

Shadowed Variables

⚠️ Delve debugger imposes variable loading limits to prevent loading too many variables at once and negatively impacting debugging latency. The dlv-dap mode uses a different approach. It takes advantage of the interactive UI features to provide on-demand loading of individual variables, paging of arrays, slices and maps and increased string limits depending on the context. We continue to explore additional interactive features to balance performance and usability of variable loading and look forward to your feedback.

You can inspect variables and evaluate expressions from the DEBUG CONSOLE panel too. Acceptable expressions are either

  • A valid Delve expression, or
  • call <function_call_expression> to call functions.

Debug Console

Variables and expressions accepted in DEBUG CONSOLE can be also registered in the Run view’s WATCH section, so they can be evaluated automatically as you debug. The "Add to Watch" feature from the VARIABLES section is convenient when you want to register interesting variables.

⚠️ Function call feature is highly EXPERIMENTAL due to the limitation in Go runtime. Registering function calls in the WATCH section can often be problematic. Pause, stop, and disconnect will not work while a function call is running.

Hover over variables in editors during debugging shows the value of the variable. For this feature, VS Code extracts the variable expression and makes a request to the debugger to evaluate the expression. Delve evaluates the expression relative to the highlighted stack frame chosen in the CALL STACK. By default, that is the current top-most frame.

Hover over Variable in Source Code

⚠️ Limitation

  • VS Code heuristically determines the variable expression without full understanding of the scope & the currently selected frame. Delve tries to evaluate the provided expression in the selected frame. As a result, hover over variables outside the selected frame’s function may present incorrect information.

Call Stack

You can inspect all goroutines and their stacks in the CALL STACK section. The CALL STACK section UI allows switching between goroutines or selecting a different stack frame. As a different stack frame or different goroutine is selected, the scope shown in the VARIABLE section will be updated for the newly selected stack frame, and the expressions in the WATCH section will be automatically reevaluated relative to the newly selected stack frame.

Call Stack Section Overview

  1. Goroutine stacks are annotated with their internal goroutine IDs.
  2. The current goroutine is marked with *. If multiple goroutines stop (e.g. hit breakpoints) concurrently, Delve will pick one randomly. There also might not be a current goroutine (e.g. deadlock, pause or internal breakpoint hit by a system thread not running a goroutine).
  3. If you click a goroutine call stack from the CALL STACK section, the goroutine is selected.
  4. You can select a frame of the selected goroutine. The VARIABLE and WATCH sections will be updated accordingly and the cursor in the editor will be moved to the corresponding location in the source code.
  5. Runtime stack frames are deemphasized (greyed out or collapsed).
  6. Thread IDs are shown for scheduled goroutines.
  7. Stop reason. It’s possible that there are multiple reasons goroutines were stopped, but currently only one reason is presented.
  8. File name and line number of the frame.
  9. You can trigger a debug action with the selected goroutine. Note: Resuming or stopping only a single goroutine (Go Issue 25578, 31132) is currently not supported, so the action will cause all the goroutines to get activated or paused.
  10. Function name of the frame.

When the program stops due to exception, panic, or bad access error, the CALL STACK shows the stop reason and the editor highlights the source location with more details.

Panic

dlv command from DEBUG CONSOLE

DEBUG CONSOLE accepts commands that allow users to dynamically inspect/change debug configuration, or inspect the list of source code compiled in the debugged binary. Use dlv help and dlv config -list from the DEBUG CONSOLE panel to see the list of supported commands and dynamically adjustable settings.

Configuration

Launch.json Attributes

There are many attributes that you can adjust in the launch and attach debug configuration. The following general attributes are mandatory for all launch configurations.

  • name: the name of your configuration as it appears in the drop-down in the Run view.
  • type: the debugging type VS Code uses to decide which debugging extension should be used. Always leave this set to "go".
  • request: launch or attach.

Here is the list of attributes specific to Go debugging.

Property Launch Attach
args Command line arguments passed to the debugged program.
 n/a
asRoot (Experimental) Debug with elevated permissions (on Unix). It requires integrated or external console modes and is ignored in remote debugging.
(Default: false)
 (Experimental) Debug with elevated permissions (on Unix). This requires integrated or external console modes and is ignored in remote debugging.
(Default: false)
backend Backend used by delve. Maps to dlv's --backend flag.

Allowed Values: "default", "native", "lldb", "rr"

 same as Launch
buildFlags Build flags, to be passed to the Go compiler. Maps to dlv's --build-flags flag.
(Default: "")
 n/a
console (Experimental) Where to launch the debugger and the debug target: internal console, integrated terminal, or external terminal. It is ignored in remote debugging.

Allowed Values: "internalConsole", "integratedTerminal", "externalTerminal"
(Default: internalConsole)

 (Experimental) Where to launch the debugger: internal console, integrated terminal, or external terminal. This does not affect tty of the running program. It is ignored in remote debugging.

Allowed Values: "internalConsole", "integratedTerminal", "externalTerminal"
(Default: internalConsole)
coreFilePath Path to the core dump file to open. For use on 'core' mode only
(Default: "")
 n/a
cwd Workspace relative or absolute path to the working directory of the program being debugged if a non-empty value is specified. The program folder is used as the working directory if cwd is omitted or empty.
(Default: "")
 Workspace relative or absolute path to the working directory of the program being debugged. Default is the current workspace.
(Default: "${workspaceFolder}")
debugAdapter Select which debug adapter to use with this launch configuration.

Allowed Values: "legacy", "dlv-dap"
(Default: dlv-dap)

 same as Launch
dlvFlags Extra flags for dlv. See dlv help for the full list of supported. Flags such as --log-output, --log, --log-dest, --api-version, --output, --backend already have corresponding properties in the debug configuration, and flags such as --listen and --headless are used internally. If they are specified in dlvFlags, they may be ignored or cause an error.
 same as Launch
env Environment variables passed to the launched debuggee program. Format as string key:value pairs. Merged with envFile and go.toolsEnvVars with precedence env > envFile > go.toolsEnvVars.
 n/a
envFile Absolute path to a file containing environment variable definitions, formatted as string key=value pairs. Multiple files can be specified by provided an array of absolute paths. Merged with env and go.toolsEnvVars with precedence env > envFile > go.toolsEnvVars.
n/a
hideSystemGoroutines Boolean value to indicate whether system goroutines should be hidden from call stack view.
(Default: false)
 same as Launch
host When applied to remote-attach configurations, will look for "dlv ... --headless --listen=:" server started externally. In dlv-dap mode this will apply to all other configurations as well. The extension will try to connect to an external server started with "dlv dap --listen=:" to ask it to launch/attach to the target process.
(Default: "127.0.0.1")
 When applied to remote-attach configurations, will look for "dlv ... --headless --listen=:" server started externally. In dlv-dap mode, this will apply to all other configurations as well. The extension will try to connect to an external server started with "dlv dap --listen=:" to ask it to launch/attach to the target process.
(Default: "127.0.0.1")
logDest dlv's --log-dest flag. See dlv log for details. Number argument is not allowed. Supported only in dlv-dap mode, and on Linux and Mac OS.
 dlv's --log-dest flag. See dlv log for details. Number argument is not allowed. Supported only in dlv-dap mode and on Linux and Mac OS.
logOutput Comma separated list of components that should produce debug output. Maps to dlv's --log-output flag. Check dlv log for details.

Allowed Values: "debugger", "gdbwire", "lldbout", "debuglineerr", "rpc", "dap"
(Default: "debugger")

 same as Launch
mode One of auto, debug, test, exec, replay, core. In auto mode, the extension will choose either debug or test depending on active editor window.

Allowed Values: "auto", "debug", "test", "exec", "replay", "core"
(Default: auto)

 Indicates local or remote debugging. Local is similar to the dlv attach command, remote - to dlv connect

Allowed Values: "local", "remote"
(Default: local)
output Output path for the binary of the debugee.
(Default: "debug")
 n/a
port When applied to remote-attach configurations, will look for "dlv ... --headless --listen=:" server started externally. In dlv-dap mode this will apply to all other configurations as well. The extension will try to connect to an external server started with "dlv dap --listen=:" to ask it to launch/attach to the target process.
(Default: 2345)
 When applied to remote-attach configurations, will look for "dlv ... --headless --listen=:" server started externally. In dlv-dap mode, this will apply to all other configurations as well. The extension will try to connect to an external server started with "dlv dap --listen=:" to ask it to launch/attach to the target process.
(Default: 2345)
processId n/a

Option 1: Use process picker to select a process to attach, or Process ID as integer.

Allowed Values: "${command:pickProcess}", "${command:pickGoProcess}"

Option 2: Attach to a process by name. If more than one process matches the name, use the process picker to select a process.

Option 3: The numeric ID of the process to be debugged. If 0, use the process picker to select a process.

(Default: 0)
program Path to the program folder (or any go file within that folder) when in debug or test mode, and to the pre-built binary file to debug in exec mode. If it is not an absolute path, the extension interpretes it as a workspace relative path.
(Default: "${workspaceFolder}")
 n/a
remotePath n/a (Deprecated) Use substitutePath instead.
The path to the source code on the remote machine, when the remote path is different from the local machine. If specified, becomes the first entry in substitutePath. Not supported with dlv-dap.
(Default: "")
showGlobalVariables Boolean value to indicate whether global package variables should be shown in the variables pane or not.
(Default: false)
 same as Launch
showLog Show log output from the delve debugger. Maps to dlv's --log flag.
(Default: false)
 same as Launch
showRegisters Boolean value to indicate whether register variables should be shown in the variables pane or not.
(Default: false)
 same as Launch
stackTraceDepth Maximum depth of stack trace collected from Delve.
(Default: 50)
 same as Launch
stopOnEntry Automatically stop program after launch.
(Default: false)
 Automatically stop program after attach.
(Default: false)
substitutePath An array of mappings from a local path (editor) to the remote path (debugee). This setting is useful when working in a file system with symbolic links, running remote debugging, or debugging an executable compiled externally. The debug adapter will replace the local path with the remote path in all of the calls.


  • "from": The absolute local path to be replaced when passing paths to the debugger.
    (Default: "")
  • "to": The absolute remote path to be replaced when passing paths back to the client.
    (Default: "")

 An array of mappings from a local path (editor) to the remote path (debugee). This setting is useful when working in a file system with symbolic links, running remote debugging, or debugging an executable compiled externally. The debug adapter will replace the local path with the remote path in all of the calls. Overriden by remotePath.


  • "from": The absolute local path to be replaced when passing paths to the debugger.
    (Default: "")
  • "to": The absolute remote path to be replaced when passing paths back to the client.
    (Default: "")
trace Various levels of logging shown in the debug console & 'Go Debug' output channel. When using the legacy debug adapter, the logs will also be written to a file if it is set to a value other than error.

Allowed Values: "verbose", "trace", "log", "info", "warn", "error"
(Default: "error")

 same as Launch
traceDirPath Directory in which the record trace is located or to be created for a new output trace. For use on 'replay' mode only
(Default: "")
 n/a

⚠️ Delve resolves relative paths from dlv dap process's working directory, but from which directory the extension spawns the dlv dap process is an implementation detail. Thus, use the VS Code variables substitution to ensure consistent expansion of paths. VS Code will resolve the variables inside strings in launch.json before passing the configuration to the Go extension and dlv dap. For example, ${workspaceFolder} will be replaced with the absolute path to the workspace root folder. When appropriate, the Go extension will resolve relative paths or home directory (~) before sending the configuration to dlv dap.

Debugging symlink directories

Since the debugger and go compiler use the actual filenames, extra configuration is required to debug symlinked directories. Use the substitutePath property to tell the debugAdapter how to properly translate the paths. For example, if your project lives in /path/to/actual/helloWorld, but the project is open in vscode under the linked folder /link/to/helloWorld, you can add the following to your config to set breakpoints in the files in /link/to/helloWorld:

{
    "name": "Launch with symlinks",
    "type": "go",
    "request": "launch",
    "mode": "debug",
    "program": "/path/to/actual/helloWorld",
    "substitutePath": [
		{
			"from": "/link/to/helloWorld",
			"to": "/path/to/actual/helloWorld",
		},
	],
}

Settings

You can adjust the default value of the following configuration properties using go.delveConfig settings. These default values are useful when you choose to run a debug session without the launch configuration set in launch.json. For example, debug sessions started using the Debug Test code lenses use the adjusted values from these settings.

  • go.delveConfig
    • debugAdapter: Controls which debug adapter to use (default: legacy). Select ‘dlv-dap’.
    • showGlobalVariables: Show global variables in the Debug view (default: false).
    • substitutePath: Path mappings to apply to get from a path in the editor to a path in the compiled program (default: []).

⚠️ Where is the dlvLoadConfig setting? Delve debugger imposes variable loading limits to avoid loading too many variables at once and negatively impacting debugging latency. The legacy adapter supported dlvLoadConfig to adjust these limits for the duration of the session. The user therefore had to come up with a one-size-fits-all limit if the default behavior was not satisfactory. dlv-dap mode uses a different approach as described in the Data Inspection section. If this setting is configured and dlv-dap mode is used, the extension will show a warning prompt now. If the current variable loading behavior and internal limits are not working for you, please open an issue and share your feedback.

dlvLoadConfig is invalid

Advanced Topics

Go Debug Extension Architecture Overview

VS Code implements a generic, language-agnostic debugger UI based on Debug Adapter Protocol (DAP), an abstract protocol for communicating with debugger backend. Previously, the Go extension used an intermediary typescript program (legacy debug adapter) to launch Delve and adapt Delve to DAP. With the new, native DAP implementation in Delve, the intermediary program is no longer necessary, and efficient and tight integration with Delve becomes possible.

vscode-go debug architecture

For information on debugging using the legacy debug adapter, please see the old Debugging Documentation. Note that many new or enhanced features discussed in this document may not be available with the legacy debug adapter.

Manually installing dlv

On rare occasions, you may want to install dlv by yourself instead of letting the extension handle its installation.

First, find where the Go extension finds tools. Like other tools the extension uses, the Go extension searches the dlv executable from ${GOPATH}/bin, ${GOBIN} and ${PATH} (or Path in Windows). So, install dlv in the directory. The easiest way to check the tool installation location the Go extension uses is currently by running the Go: Locate Configured Go Tools command from the command palette (⇧+⌘+P or Ctrl+Shift+P).

If your Go version is 1.16 or newer:

$ GOBIN=<dir_to_install_dlv> go install github.com/go-delve/delve/cmd/dlv@latest

If your Go version is older than 1.16:

$ cd $(mktemp -d)
$ GO111MODULE=on GOBIN=<dir_to_install_dlv> go get github.com/go-delve/delve/cmd/dlv@latest

You can choose to install a different version of dlv by specifying a specific commit hash, a branch name (e.g. master), or a released version instead of latest. For more details about manual installation, see Delve's documentation.

If you want to explicitly specify the location of the delve binary, use the go.alternateTools setting:

"go.alternateTools": {
    "dlv": "<absolute path to your dlv binary>"
}

Remote Debugging

If you are able to use the Remote Development extensions and VS Code’s universal remote development capabilities, that is the recommended way to debug Go programs remotely. Check out Getting started section and Remote tutorials to learn more.

Remote debugging is the debug mode commonly used to work with a debugger and target running on a remote machine or a container. In spite of its name, it can also be used on a local machine with server started in an external terminal (e.g. to support entering stdin into the server's terminal window).

With the introduction of dlv dap users now have two options for remote (i.e. external) debugging.

Connecting to Headless Delve with Target Specified at Server Start-Up

In this mode the user must first manually start a dlv --headless server listening at host:port while specifying the target program to debug/test/exec or a process to attach to on the command-line. A remote attach configuration is then used to connect to the debugger with a running target.

The headless dlv server can now be used with both "debugAdapter": "legacy" (default value) and "debugAdapter": "dlv-dap" (with Delve v1.7.3 or newer) as well as Delve's command-line interface via dlv connect. The --accept-multiclient flag makes this a multi-use server that persists on Disconnect from a client and allows repeated connections from any of the aforementioned clients. A combination of --accept-multiclient --continue flags can be used to resume process execution on start-up. Please see dlv --help and dlv [command] --help for dlv's command-line options.

We encourage you to give the newly added "debugAdapter": "dlv-dap" support a try and to let us know of any issues. If you need to use the legacy mode, pleasse also see the legacy remote debugging documentation.

For example, start external headless server:

dlv debug /path/to/program/ --headless --listen=:12345 # also add as needed: --accept-multiclient --continue

Connect to it with a remote attach configuration in your launch.json:

{
    "name": "Connect to external session",
    "type": "go",
    "debugAdapter": "dlv-dap", // `legacy` by default
    "request": "attach",
    "mode": "remote",
    "port": 12345,
    "host": "127.0.0.1", // can skip for localhost
    "substitutePath": [
      { "from": ${workspaceFolder}, "to": "/path/to/remote/workspace" },
      ...
  ]
}

Connecting to Delve DAP with Target Specified at Client Start-Up

In this mode the user must first manually start a dlv dap server listening at host:port and then specify the target program via launch or attach client config with a "port" attribute. Instead of starting a new local server, the Go extension will tell VS Code to connect to the server specified by host:port attributes and then send a request with the target to debug. This option provides the flexibility of easily adapting local configurations to connect to external servers, but ⚠️ must be used with care since anyone who can connect to the server can make it run arbitrary programs.

When using launch mode, the program attribute must point to the absolute path of the package or binary to debug in the remote host’s file system even when substitutePath is specified. When using attach mode outside of local host, you need to specify the processId in the config since the processId resolution feature cannot gather information about processes running remotely.

Start a dlv dap server ready to accept a client request to launch or attach to a target process:

$ dlv dap --listen=:12345

Use the following launch configuration to tell dlv to execute a binary precompiled with go build -gcflags='all=-N -l':

{
  "name": "Connect and launch",
  "type": "go",
  "debugAdapter": "dlv-dap", // the default
  "request": "launch",
  "port": 12345,
  "host": "127.0.0.1", // can skip for localhost
  "mode": "exec",
  "program": "/absolute/path/to/remote/workspace/program/executable",
  "substitutePath": [
      { "from": ${workspaceFolder}, "to": "/path/to/remote/workspace" },
      ...
  ]
}

Or have the binary compiled by dlv dap by modifying the above configuration to use:

  "mode": "debug",
  "program": "/absolute/path/to/remote/workspace/package",

⚠️ Limitations

  • Unlike dlv --headless above, dlv dap does not support --accept-multiclient or --continue flags, which means after a debug session ends, the dlv dap process will always exit.
  • If you use debug or test mode launch requests, Delve builds the target binary. Delve tries to build the target from the directory where the dlv process is running, so make sure to run the dlv command from the directory you would run the go build or go test command.

Running Debugee Externally

Sometimes you might like to launch the program for debugging outside of VS Code (e.g. as a workaround of the missing console support to enter stdin via an external terminal or separate target's output from debug session logging). There are currently two options:

  • Compile and run the target program from the external terminal and use the "attach" configuration.
  • Run the debug server from the external terminal with --listen=:<port> and have VS Code connect to it using port in your launch configuration (see "Remote Debugging" for more details)

Troubleshooting

The suggestions below are intended to help you troubleshoot any problems you encounter. If you are unable to resolve the issue, please take a look at the current known debugging issues or report a new issue.

  1. Read documentation and FAQs. Also check the Delve FAQ in case the problem is mentioned there.
  2. Check your launch.json configuration. Often error messages appearing in the DEBUG CONSOLE panel reveal issues.
  3. Update Delve (dlv) to pick up most recent bug fixes. Follow the instruction.
  4. Check if you can reproduce the issue with dlv, the command line tool from the integrated terminal. If it's reproducible when using dlv, take a look at the Delve project issue tracker.
  5. Capture logs and inspect them.
  6. Look at the existing debugging issues if similar issues were reported.
  7. If none of these solve your problem, please open a new issue.

FAQs

I need to view large strings. How can I do that if dlvLoadConfig with maxStringLen is deprecated?

The legacy adapter used dlvLoadConfig as one-time session-wide setting to override dlv's conservative default variable loading limits, intended to protect tool's performance. The new debug adapter is taking a different approach with on-demand loading of composite data and updated string limits, relaxed when interacting with individual strings. In particular, if the new default limit of 512, applied to all string values in the variables pane, is not sufficient, you can take advantage of a larger limit of 4096 with one of the following:

  • Hover over the variable in the source code
  • Copy as Expression to query the string via REPL in the DEBUG CONSOLE panel
  • Copy Value to clipboard

Please open an issue if this is not sufficient for your use case or if you have any additional feedback.

Why does my debug session have an invalid command error when I try to step?

When stepping through a program on a particular goroutine, the debugger will make sure that the step is completed, even when interrupted by events on a different goroutine. If a breakpoint is hit on a different goroutine, the debug adapter will stop the program execution to allow you to inspect the state, even though the step request is still active.

If you attempt to make another step request you will get an invalid command error.

Disable breakpoints from the Breakpoints context menu

Use Continue to resume program execution.

If you do not want the step request to be interrupted, you can disable all breakpoints from VS Code from the context menu in the Breakpoints view.

Disable breakpoints from the Breakpoints context menu

My program does not stop at breakpoints.

Check the "BREAKPOINTS" section in the debug view and see if the breakpoints are greyed out when your debug session is active. Setting stopOnEntry is a great way to pause execution at the start to verify breakpoints are set correctly. Or enable logging and see if setBreakpoints requests succeeded with all the breakpoints verified.

This problem often occurs when the source location used in compiling the debugged program and the workspace directory VS Code uses are different. Common culprits are remote debugging where the program is built in the remote location, use of symbolic links, or use of -trimpath build flags. In this case, configure the substitutePath attribute in your launch configuration.

Debug sessions started with the "debug test" CodeLens or the test UI does not use my launch.json configuration.

The "debug test" CodeLens and the test UI do not use the launch.json configuration (Issue 855). As a workaround, use the go.delveConfig setting and the go.testFlags setting. Please note that these all apply to all debug sessions unless overwritten by a specific launch.json configuration.

Starting a debug session fails with decoding dwarf section info at offset 0x0: too short or could not open debug info error.

These errors indicate that your binary was built with linker flags that stripped the symbol table (-s) or the DWARF debug information (-w), making debugging impossible. If the binary is built while launching the session, make sure your launch.json configuration does not contain "buildFlags": "--ldflags '-s -w'". If you use debug test or Test Explorer, check go.buildFlags in settings.json. If the binary is built externally, check the command-line flags and do not use go run. Unlike go build, go run passes -s -w to the linker under the hood. If you try to attach to such a binary with a debugger, it will fail with one of the above errors (see Go Issue 24833). Instead let dlv build the binary for you or use go build -gcflags='all=-N -l'.

Reporting Issues

When you are having issues in dlv-dap mode, first check if the problems are reproducible after updating dlv and using the most recent version of dlv. It's possible that the problems are already fixed. You can also try to install dlv at tree head. Follow the instruction for updating dlv and updating extension.

Please report issues in our issue tracker with the following information.

  • go version
  • go version -m <path/to/dlv>
  • VS Code and VS Code Go version (e.g. code --version)
  • Instructions to reproduce the issue (code snippets, your launch.json, screenshot)
  • DAP trace (See the instruction)

Collecting Logs

{
    "name": "Launch file",
    "type": "go",
    "trace": "verbose",
    "showLog": true,
    "logOutput": "dap",
    ...
}

The logOutput and showLog attributes in launch.json enable Delve-side logging (server-side) and DAP message tracing. The trace attribute controls the verbosity of Go extension's side logging (client-side).

The logging will appear in the Go Debug output channel (Command Palette -> "View: Toggle Output" -> Select "Go Debug" from the dropdown menu). By nature, debug logs may contain sensitive information. Please review the logs carefully before sharing debug logs.

Developing

Code location

The core part of Delve DAP implementation is in the service/dap package. Follow Delve project's contribution guideline to send PRs.

Code for integration with the Go extension is mostly in src/goDebugFactory.ts and tests are in test/integration/goDebug.test.ts. Please take a look at VS Code Go project's contribution guideline to learn about how to prepare a change and send it for review.

Testing

For simple launch cases, build the dlv binary, and configure "go.alternateTools" setting.

"go.alternateTools": {
    "dlv": <path_to_your_dlv>
}

Go Debug output channel

If you are having issues with seeing logs and/or suspect problems in the extension's integration, you can start the Delve DAP server from a separate terminal and configure the extension to directly connect to it. Please remember to [file an issue](https://github.com/golang/vscode-go/issues/new) if you encounter any logging-related problems. 
$ dlv dap --listen=:12345 --log --log-output=dap

{
    "name": "Launch file",
    "type": "go",
    "request": "launch",
    "debugAdapter": "dlv-dap",
    ...
    "port": 12345
}