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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](https://code.visualstudio.com/docs/editor/debugging).
These debugging features are possible by using [Delve](https://github.com/go-delve/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](https://github.com/go-delve/delve/tree/master/service/dap) 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](https://microsoft.github.io/debug-adapter-protocol/overview).
📣 **We are happy to announce that now this new mode of Delve integration (_`dlv-dap`_ mode) is enabled for _local_ _debugging_ by default and is available for [_remote_ _debugging_](#remote-debugging) on demand!**
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](https://github.com/golang/vscode-go/tree/master/docs/debugging-legacy.md).
## 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](https://code.visualstudio.com/docs/editor/debugging#_run-view). Alternatively, you can start debugging using `Start Debugging (F5)` command from [the Run menu](https://code.visualstudio.com/docs/editor/debugging#_run-menu) or from [the Command Palette](https://code.visualstudio.com/docs/getstarted/userinterface#_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.
<p align="center">
<img src="images/dlvdap-install.gif" alt="Delve Install" width="75%"><!--TODO: update image-->
<br/>
<em>❗ 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).</em>
</p>
<div style="text-align: center;"></div>
Watch ["Go: Writing and debugging fast, reliable, and efficient software"](https://www.youtube.com/watch?v=6r08zGi38Tk&list=PLj6YeMhvp2S40Q-TEPEKOeypLvTVd5uME&index=1) to learn more about debugging features.
Please review [the Features section](#features) that provides an overview of the debug UI and available features.
### Staying Up-To-Date
[Delve’s native DAP implementation](https://github.com/go-delve/delve/tree/master/service/dap) 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`](https://github.com/golang/vscode-go/blob/master/docs/debugging.md#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](#launchjson-attributes) 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](https://github.com/golang/vscode-go/issues/new)
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](https://code.visualstudio.com/docs/editor/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](https://code.visualstudio.com/docs/editor/debugging#_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](https://code.visualstudio.com/docs/editor/debugging#_global-launch-configuration) or [workspace settings](https://code.visualstudio.com/docs/editor/multi-root-workspaces#_workspace-launch-configurations).
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.
<p align="center">
<img src="images/create-launch-json.gif" alt="Create launch.json" width="75%">
</p>
There are many configuration attributes (see [the Launch.json attributes](#launchjson-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"](#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.
<p align="center">
<img src="images/attach.gif" alt="Attach to a running process" width="75%">
</p>
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"](#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"](#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.
<p align="center">
<img src="images/attach-terminate.gif" alt="Terminate Debugging started with Attach" style="width: 30%">
</p>
<!-- TODO:[SupportSuspendDebuggee](https://code.visualstudio.com/updates/v1_56#_disconnect-debugger-and-keep-debuggee-suspended) -->
### Debug Actions
Once a debug session starts, the Debug toolbar will appear on the top of the editor.
<p align="center">
<img src="images/debug-toolbar.png" alt="Debug Tool Bar" width="30%">
</p>
* 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](https://code.visualstudio.com/docs/editor/debugging#_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.
<p align="center">
<img src="images/invalid-breakpoint.png" alt="Invalid breakpoint" width="75%">
</p>
* **Conditional breakpoints**: you can specify breakpoint conditions (similar to Delve’s [`condition` command](https://github.com/go-delve/delve/tree/master/Documentation/cli#condition)).
* 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`.
<p align="center">
<img src="images/conditional-breakpoint.gif" alt="Conditional Breakpoint" width="50%">
</p>
* **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](https://github.com/go-delve/delve/blob/master/Documentation/cli/locspec.md#location-specifiers). Function breakpoints are shown with a red triangle in the BREAKPOINTS section.
<p align="center">
<img src="images/function-breakpoint.gif" alt="Function breakpoint" width="75%">
</p>
* **Logpoints**: a [logpoint](https://code.visualstudio.com/docs/editor/debugging#_logpoints) 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](https://github.com/go-delve/delve/blob/master/Documentation/cli/expr.md#expressions).
### 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 `()`.
<p align="center">
<img src="images/shadowed-variables.png" alt="Shadowed Variables" style="width: 50%">
</p>
⚠️ 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](https://github.com/go-delve/delve/blob/master/Documentation/cli/expr.md), or
* `call <function_call_expression>` to call functions.
<p align="center">
<img src="images/debug-console.png" alt="Debug Console" width="50%">
</p>
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.
<p align="center"><img src="images/variable-hover.png" alt="Hover over Variable in Source Code" width="50%">
</p>
⚠️ 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.
<p align="center"><img src="images/callstack-section-annotated.gif" alt="Call Stack Section Overview" width="75%"> </p>
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](https://github.com/golang/go/issues/25578), [31132](https://github.com/golang/go/issues/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.
<p align="center"><img src="images/panicinfo.png" alt="Panic" width="75%"></p>
## `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.
<!-- DO NOT EDIT: Auto-generated by go run tools/generate -->
<!-- SETTINGS BEGIN -->
| Property | Launch | Attach |
| --- | --- | --- |
| `args` | Command line arguments passed to the debugged program.<br/> | <center>_n/a_</center> |
| `asRoot` | (Experimental) Debug with elevated permissions (on Unix). It requires `integrated` or `external` console modes and is ignored in remote debugging.<br/>(Default: `false`)<br/> | (Experimental) Debug with elevated permissions (on Unix). This requires `integrated` or `external` console modes and is ignored in remote debugging.<br/>(Default: `false`)<br/> |
| `backend` | Backend used by delve. Maps to `dlv`'s `--backend` flag.<br/><p>Allowed Values: `"default"`, `"native"`, `"lldb"`, `"rr"`<br/> | <center>_same as Launch_</center>|
| `buildFlags` | Build flags, to be passed to the Go compiler. Maps to dlv's `--build-flags` flag.<br/>(Default: `""`)<br/> | <center>_n/a_</center> |
| `console` | (Experimental) Where to launch the debugger and the debug target: internal console, integrated terminal, or external terminal. It is ignored in remote debugging.<br/><p>Allowed Values: `"internalConsole"`, `"integratedTerminal"`, `"externalTerminal"`<br/>(Default: `internalConsole`)<br/> | (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.<br/><p>Allowed Values: `"internalConsole"`, `"integratedTerminal"`, `"externalTerminal"`<br/>(Default: `internalConsole`)<br/> |
| `coreFilePath` | Path to the core dump file to open. For use on 'core' mode only<br/>(Default: `""`)<br/> | <center>_n/a_</center> |
| `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.<br/>(Default: `""`)<br/> | Workspace relative or absolute path to the working directory of the program being debugged. Default is the current workspace.<br/>(Default: `"${workspaceFolder}"`)<br/> |
| `debugAdapter` | Select which debug adapter to use with this launch configuration.<br/><p>Allowed Values: `"legacy"`, `"dlv-dap"`<br/>(Default: `dlv-dap`)<br/> | <center>_same as Launch_</center>|
| `dlvFlags` | Extra flags for `dlv`. See `dlv help` for the full list of supported. Flags such as `--log-output`, `--log`, `--log-dest`, `--api-version`, `--output`, `--backend` already have corresponding properties in the debug configuration, and flags such as `--listen` and `--headless` are used internally. If they are specified in `dlvFlags`, they may be ignored or cause an error.<br/> | <center>_same as Launch_</center>|
| `env` | Environment variables passed to the program.<br/> | <center>_n/a_</center> |
| `envFile` | Absolute path to a file containing environment variable definitions. Multiple files can be specified by provided an array of absolute paths<br/>(Default: `${workspaceFolder}/.env`)<br/> | <center>_n/a_</center> |
| `hideSystemGoroutines` | Boolean value to indicate whether system goroutines should be hidden from call stack view.<br/>(Default: `false`)<br/> | <center>_same as Launch_</center>|
| `host` | When applied to remote-attach configurations, will look for "dlv ... --headless --listen=<host>:<port>" 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=<host>:<port>" to ask it to launch/attach to the target process.<br/>(Default: `"127.0.0.1"`)<br/> | When applied to remote-attach configurations, will look for "dlv ... --headless --listen=<host>:<port>" 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=<host>:<port>" to ask it to launch/attach to the target process.<br/>(Default: `"127.0.0.1"`)<br/> |
| `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.<br/> | 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.<br/> |
| `logOutput` | Comma separated list of components that should produce debug output. Maps to dlv's `--log-output` flag. Check `dlv log` for details.<br/><p>Allowed Values: `"debugger"`, `"gdbwire"`, `"lldbout"`, `"debuglineerr"`, `"rpc"`, `"dap"`<br/>(Default: `"debugger"`)<br/> | <center>_same as Launch_</center>|
| `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.<br/><p>Allowed Values: `"auto"`, `"debug"`, `"test"`, `"exec"`, `"replay"`, `"core"`<br/>(Default: `auto`)<br/> | Indicates local or remote debugging. Local is similar to the `dlv attach` command, remote - to `dlv connect`<br/><p>Allowed Values: `"local"`, `"remote"`<br/>(Default: `local`)<br/> |
| `output` | Output path for the binary of the debugee.<br/>(Default: `"debug"`)<br/> | <center>_n/a_</center> |
| `port` | When applied to remote-attach configurations, will look for "dlv ... --headless --listen=<host>:<port>" 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=<host>:<port>" to ask it to launch/attach to the target process.<br/>(Default: `2345`)<br/> | When applied to remote-attach configurations, will look for "dlv ... --headless --listen=<host>:<port>" 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=<host>:<port>" to ask it to launch/attach to the target process.<br/>(Default: `2345`)<br/> |
| `processId` | <center>_n/a_</center> | <br/><p><b>Option 1:</b> Use process picker to select a process to attach, or Process ID as integer.<br/><p>Allowed Values: `"${command:pickProcess}"`, `"${command:pickGoProcess}"`<br/><br/><p><b>Option 2:</b> Attach to a process by name. If more than one process matches the name, use the process picker to select a process.<br/><br/><p><b>Option 3:</b> The numeric ID of the process to be debugged. If 0, use the process picker to select a process.<br/><br/>(Default: `0`)<br/> |
| `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.<br/>(Default: `"${workspaceFolder}"`)<br/> | <center>_n/a_</center> |
| `remotePath` | <center>_n/a_</center> | (Deprecated) *Use `substitutePath` instead.*<br/>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`.<br/>(Default: `""`)<br/> |
| `showGlobalVariables` | Boolean value to indicate whether global package variables should be shown in the variables pane or not.<br/>(Default: `false`)<br/> | <center>_same as Launch_</center>|
| `showLog` | Show log output from the delve debugger. Maps to dlv's `--log` flag.<br/>(Default: `false`)<br/> | <center>_same as Launch_</center>|
| `showRegisters` | Boolean value to indicate whether register variables should be shown in the variables pane or not.<br/>(Default: `false`)<br/> | <center>_same as Launch_</center>|
| `stackTraceDepth` | Maximum depth of stack trace collected from Delve.<br/>(Default: `50`)<br/> | <center>_same as Launch_</center>|
| `stopOnEntry` | Automatically stop program after launch.<br/>(Default: `false`)<br/> | Automatically stop program after attach.<br/>(Default: `false`)<br/> |
| `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.<br/><p><br/><ul><li>`"from"`: The absolute local path to be replaced when passing paths to the debugger.<br/>(Default: `""`)<br/></li><li>`"to"`: The absolute remote path to be replaced when passing paths back to the client.<br/>(Default: `""`)<br/></li></ul><br/> | 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`.<br/><p><br/><ul><li>`"from"`: The absolute local path to be replaced when passing paths to the debugger.<br/>(Default: `""`)<br/></li><li>`"to"`: The absolute remote path to be replaced when passing paths back to the client.<br/>(Default: `""`)<br/></li></ul><br/> |
| `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`.<br/><p>Allowed Values: `"verbose"`, `"trace"`, `"log"`, `"info"`, `"warn"`, `"error"`<br/>(Default: `"error"`)<br/> | <center>_same as Launch_</center>|
| `traceDirPath` | Directory in which the record trace is located or to be created for a new output trace. For use on 'replay' mode only<br/>(Default: `""`)<br/> | <center>_n/a_</center> |
<!-- SETTINGS END -->
⚠️ 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](https://code.visualstudio.com/docs/editor/variables-reference) 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",
},
],
}
```
<!--### Options for "Add Configuration"
TODO: clean up the snippets in package.json
TODO: auto-generate from package.json. -->
### 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`](settings.md#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](#data-inspection). 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](https://github.com/golang/vscode-go/issues/new) and share your feedback.
<p align="center"><img src="images/dlv-load-config-warning.png" alt="dlvLoadConfig is invalid" width="50%"> </p>
## Advanced Topics
### Go Debug Extension Architecture Overview
VS Code implements a generic, language-agnostic debugger UI based on [Debug Adapter Protocol](https://microsoft.github.io/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](https://github.com/go-delve/delve/tree/master/service/dap), the intermediary program is no longer necessary, and efficient and tight integration with Delve becomes possible.
<p align="center"><img src="images/vscode-go-debug-arch.png" alt="vscode-go debug architecture"> </p>
For information on debugging using the legacy debug adapter, please see the old [Debugging Documentation](https://github.com/golang/vscode-go/blob/master/docs/debugging.md). 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](https://github.com/golang/vscode-go/blob/master/docs/tools.md#tools), 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](https://github.com/go-delve/delve/tree/master/Documentation/installation).
If you want to explicitly specify the location of the delve binary, use the `go.alternateTools` setting:
```json5
"go.alternateTools": {
"dlv": "<absolute path to your dlv binary>"
}
```
### Remote Debugging
> If you are able to use the [Remote Development](https://aka.ms/vscode-remote/download/extension) extensions and VS Code’s universal [remote development capabilities](https://code.visualstudio.com/docs/remote/remote-overview), that is the recommended way to debug Go programs remotely. Check out [Getting started](https://code.visualstudio.com/docs/remote/remote-overview#_getting-started) section and [Remote tutorials](https://code.visualstudio.com/docs/remote/remote-overview#_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`](https://github.com/go-delve/delve/tree/master/Documentation/api) 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](#attach) configuration is then used to connect to the debugger with a running target.
The [headless dlv server](https://github.com/go-delve/delve/tree/master/Documentation/api) 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](https://github.com/go-delve/delve/tree/master/Documentation/cli) 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](https://github.com/golang/vscode-go/issues/new). If you need to use the `legacy` mode, pleasse also see the [legacy remote debugging](https://github.com/golang/vscode-go/blob/master/docs/debugging-legacy.md#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`:
```json5
{
"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](https://github.com/go-delve/delve/blob/master/Documentation/usage/dlv_dap.md) listening at `host:port` and then specify the target program via [launch](#launch) or [attach](#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](#attach) cannot gather information about processes running remotely.
<!-- TODO: update or remote this picture
<p align="center"><img src="images/remote-debugging.png" alt="Remote Debugging"> </p>
-->
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'`:
```json5
{
"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:
```json5
"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](#attach).
* 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"](#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](https://github.com/golang/vscode-go/issues?q=is%3Aissue+is%3Aopen+label%3ADebug) or [report a new issue](#reporting-issues).
1. Read documentation and [FAQs](#faqs). Also check the [Delve FAQ](https://github.com/go-delve/delve/blob/master/Documentation/faq.md) in case the problem is mentioned there.
1. Check your `launch.json` configuration. Often error messages appearing in the DEBUG CONSOLE panel reveal issues.
1. Update Delve (`dlv`) to pick up most recent bug fixes. Follow [the instruction](https://github.com/golang/vscode-go/blob/master/docs/debugging.md#staying-up-to-date).
1. Check if you can reproduce the issue with `dlv`, the command line tool from the integrated terminal. <!-- TODO(vscode-go): add instructions https://github.com/golang/vscode-go/issues/1931 --> If it's reproducible when using `dlv`, take a look at the [Delve project issue tracker](https://github.com/go-delve/delve/issues).
1. Capture [logs](https://github.com/golang/vscode-go/blob/master/docs/debugging.md#collecting-logs) and inspect them.
1. Look at the [existing debugging issues](https://github.com/golang/vscode-go/labels/Debug) if similar issues were reported.
1. If none of these solve your problem, please [open a new issue](#reporting-issues).
## 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](https://github.com/golang/vscode-go/issues/new) 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.
<p align="center"><img src="images/invalidCommandExceptionInfo.png" alt="Disable breakpoints from the Breakpoints context menu" width="75%"> </p>
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.
<p align="center"><img src="images/disablebps.png" alt="Disable breakpoints from the Breakpoints context menu" width="75%"> </p>
### My program does not stop at breakpoints.
Check the "BREAKPOINTS" section in the debug view and see if the breakpoints are [greyed out](https://code.visualstudio.com/docs/editor/debugging#_breakpoints) 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](#collecting-logs) 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](https://github.com/golang/vscode-go/blob/master/docs/features.md#test-and-benchmark) do not use the `launch.json` configuration ([Issue 855](https://github.com/golang/vscode-go/issues/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.
### Why can't I use local attach with a process started with `go run`?
Unlike `go build`, `go run` passes `-s -w` to the linker to strip the debug info. If you try attach to such a binary with a debugger, it will fail an error like `decoding dwarf section info at offset 0x0: too short`. Use `go build -gcflags='all=-N -l'` to build your binary instead. See Go Issue [24833](https://github.com/golang/go/issues/24833) for more information.
## 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`](#staying-up-to-date) and [updating extension](https://code.visualstudio.com/docs/editor/extension-gallery#\_extension-autoupdate).
Please report issues in [our issue tracker](https://github.com/golang/vscode-go/issues) 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))
### Collecting Logs
```json5
{
"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`](https://github.com/go-delve/delve/tree/master/service/dap) package. Follow Delve project's [contribution guideline](https://github.com/go-delve/delve/blob/master/CONTRIBUTING.md#contributing-code) to send PRs.
Code for integration with the Go extension is mostly in [`src/goDebugFactory.ts`](https://github.com/golang/vscode-go/blob/master/src/goDebugFactory.ts) and tests are in [`test/integration/goDebug.test.ts`](https://github.com/golang/vscode-go/blob/master/test/integration/goDebug.test.ts). Please take a look at VS Code Go project's [contribution guideline](https://github.com/golang/vscode-go/blob/master/docs/contributing.md) 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.
```json5
"go.alternateTools": {
"dlv": <path_to_your_dlv>
}
```
<p align="center"><img src="images/debug-output.png" alt="Go Debug output channel" width="100%"></p>
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
```
```json5
{
"name": "Launch file",
"type": "go",
"request": "launch",
"debugAdapter": "dlv-dap",
...
"port": 12345
}
```
[Delve]: https://github.com/go-delve/delve
[VS Code variables]: https://code.visualstudio.com/docs/editor/variables-reference
[snippets]: https://code.visualstudio.com/docs/editor/userdefinedsnippets
[Command Palette]: https://code.visualstudio.com/docs/getstarted/userinterface#_command-palette