# Debugger

Zed uses the [Debug Adapter Protocol (DAP)](https://microsoft.github.io/debug-adapter-protocol/) to provide debugging functionality across multiple programming languages.
DAP is a standardized protocol that defines how debuggers, editors, and IDEs communicate with each other.
It allows Zed to support various debuggers without needing to implement language-specific debugging logic.
Zed implements the client side of the protocol, and various _debug adapters_ implement the server side.

This protocol enables features like setting breakpoints, stepping through code, inspecting variables,
and more, in a consistent manner across different programming languages and runtime environments.

## Supported Languages

To debug code written in a specific language, Zed needs to find a debug adapter for that language. Some debug adapters are provided by Zed without additional setup, and some are provided by [language extensions](./extensions/debugger-extensions.md). The following languages currently have debug adapters available:

<!-- keep this sorted -->

- [C](./languages/c.md#debugging) (built-in)
- [C++](./languages/cpp.md#debugging) (built-in)
- [Go](./languages/go.md#debugging) (built-in)
- [JavaScript](./languages/javascript.md#debugging) (built-in)
- [PHP](./languages/php.md#debugging) (built-in)
- [Python](./languages/python.md#debugging) (built-in)
- [Ruby](./languages/ruby.md#debugging) (provided by extension)
- [Rust](./languages/rust.md#debugging) (built-in)
- [Swift](./languages/swift.md#debugging) (provided by extension)
- [TypeScript](./languages/typescript.md#debugging) (built-in)

> If your language isn't listed, you can contribute by adding a debug adapter for it. Check out our [debugger extensions](./extensions/debugger-extensions.md) documentation for more information.

Follow those links for language- and adapter-specific information and examples, or read on for more about Zed's general debugging features that apply to all adapters.

## Getting Started

For most languages, the fastest way to get started is to run {#action debugger::Start} ({#kb debugger::Start}). This opens the _new process modal_, which shows you a contextual list of preconfigured debug tasks for the current project. Debug tasks are created from tests, entry points (like a `main` function), and from other sources — consult the documentation for your language for full information about what's supported.

You can open the same modal by clicking the "plus" button at the top right of the debug panel.

For languages that don't provide preconfigured debug tasks (this includes C, C++, and some extension-supported languages), you can define debug configurations in the `.zed/debug.json` file in your project root. This file should be an array of configuration objects:

```json
[
  {
    "adapter": "CodeLLDB",
    "label": "First configuration"
    // ...
  },
  {
    "adapter": "Debugpy",
    "label": "Second configuration"
    // ...
  }
]
```

Check the documentation for your language for example configurations covering typical use-cases. Once you've added configurations to `.zed/debug.json`, they'll appear in the list in the new process modal.

Zed will also load debug configurations from `.vscode/launch.json`, and show them in the new process modal if no configurations are found in `.zed/debug.json`.

### Launching & Attaching

Zed debugger offers two ways to debug your program; you can either _launch_ a new instance of your program or _attach_ to an existing process.
Which one you choose depends on what you are trying to achieve.

When launching a new instance, Zed (and the underlying debug adapter) can often do a better job at picking up the debug information compared to attaching to an existing process, since it controls the lifetime of a whole program.
Running unit tests or a debug build of your application is a good use case for launching.

Compared to launching, attaching to an existing process might seem inferior, but that's far from truth; there are cases where you cannot afford to restart your program, because for example, the bug is not reproducible outside of a production environment or some other circumstances.

## Configuration

While configuration fields are debug adapter-dependent, most adapters support the following fields:

```json
[
  {
    // The label for the debug configuration and used to identify the debug session inside the debug panel & new process modal
    "label": "Example Start debugger config",
    // The debug adapter that Zed should use to debug the program
    "adapter": "Example adapter name",
    // Request:
    //  - launch: Zed will launch the program if specified, or show a debug terminal with the right configuration
    //  - attach: Zed will attach to a running program to debug it, or when the process_id is not specified, will show a process picker (only supported for node currently)
    "request": "launch",
    // The program to debug. This field supports path resolution with ~ or . symbols.
    "program": "path_to_program",
    // cwd: defaults to the current working directory of your project ($ZED_WORKTREE_ROOT)
    "cwd": "$ZED_WORKTREE_ROOT"
  }
]
```

All configuration fields support [task variables](./tasks.md#variables).

### Build tasks

Zed also allows embedding a Zed task in a `build` field that is run before the debugger starts. This is useful for setting up the environment or running any necessary setup steps before the debugger starts.

```json
[
  {
    "label": "Build Binary",
    "adapter": "CodeLLDB",
    "program": "path_to_program",
    "request": "launch",
    "build": {
      "command": "make",
      "args": ["build", "-j8"]
    }
  }
]
```

Build tasks can also refer to the existing tasks by unsubstituted label:

```json
[
  {
    "label": "Build Binary",
    "adapter": "CodeLLDB",
    "program": "path_to_program",
    "request": "launch",
    "build": "my build task" // Or "my build task for $ZED_FILE"
  }
]
```

### Automatic scenario creation

Given a Zed task, Zed can automatically create a scenario for you. Automatic scenario creation also powers our scenario creation from gutter.
Automatic scenario creation is currently supported for Rust, Go, Python, JavaScript, and TypeScript.

## Breakpoints

To set a breakpoint, simply click next to the line number in the editor gutter.
Breakpoints can be tweaked depending on your needs; to access additional options of a given breakpoint, right-click on the breakpoint icon in the gutter and select the desired option.
At present, you can:

- Add a log to a breakpoint, which will output a log message whenever that breakpoint is hit.
- Make the breakpoint conditional, which will only stop at the breakpoint when the condition is met. The syntax for conditions is adapter-specific.
- Add a hit count to a breakpoint, which will only stop at the breakpoint after it's hit a certain number of times.
- Disable a breakpoint, which will prevent it from being hit while leaving it visible in the gutter.

Some debug adapters (e.g. CodeLLDB and JavaScript) will also _verify_ whether your breakpoints can be hit; breakpoints that cannot be hit are surfaced more prominently in the UI.

All breakpoints enabled for a given project are also listed in "Breakpoints" item in your debugging session UI. From "Breakpoints" item in your UI you can also manage exception breakpoints.
The debug adapter will then stop whenever an exception of a given kind occurs. Which exception types are supported depends on the debug adapter.

## Settings

The settings for the debugger are grouped under the `debugger` key in `settings.json`:

- `dock`: Determines the position of the debug panel in the UI.
- `stepping_granularity`: Determines the stepping granularity.
- `save_breakpoints`: Whether the breakpoints should be reused across Zed sessions.
- `button`: Whether to show the debug button in the status bar.
- `timeout`: Time in milliseconds until timeout error when connecting to a TCP debug adapter.
- `log_dap_communications`: Whether to log messages between active debug adapters and Zed.
- `format_dap_log_messages`: Whether to format DAP messages when adding them to the debug adapter logger.

### Dock

- Description: The position of the debug panel in the UI.
- Default: `bottom`
- Setting: debugger.dock

**Options**

1. `left` - The debug panel will be docked to the left side of the UI.
2. `right` - The debug panel will be docked to the right side of the UI.
3. `bottom` - The debug panel will be docked to the bottom of the UI.

```json
"debugger": {
  "dock": "bottom"
},
```

### Stepping granularity

- Description: The Step granularity that the debugger will use
- Default: `line`
- Setting: `debugger.stepping_granularity`

**Options**

1. Statement - The step should allow the program to run until the current statement has finished executing.
   The meaning of a statement is determined by the adapter and it may be considered equivalent to a line.
   For example 'for(int i = 0; i < 10; i++)' could be considered to have 3 statements 'int i = 0', 'i < 10', and 'i++'.

```json
{
  "debugger": {
    "stepping_granularity": "statement"
  }
}
```

2. Line - The step should allow the program to run until the current source line has executed.

```json
{
  "debugger": {
    "stepping_granularity": "line"
  }
}
```

3. Instruction - The step should allow one instruction to execute (e.g. one x86 instruction).

```json
{
  "debugger": {
    "stepping_granularity": "instruction"
  }
}
```

### Save Breakpoints

- Description: Whether the breakpoints should be saved across Zed sessions.
- Default: `true`
- Setting: `debugger.save_breakpoints`

**Options**

`boolean` values

```json
{
  "debugger": {
    "save_breakpoints": true
  }
}
```

### Button

- Description: Whether the button should be displayed in the debugger toolbar.
- Default: `true`
- Setting: `debugger.show_button`

**Options**

`boolean` values

```json
{
  "debugger": {
    "show_button": true
  }
}
```

### Timeout

- Description: Time in milliseconds until timeout error when connecting to a TCP debug adapter.
- Default: `2000`
- Setting: `debugger.timeout`

**Options**

`integer` values

```json
{
  "debugger": {
    "timeout": 3000
  }
}
```

### Inline Values

- Description: Whether to enable editor inlay hints showing the values of variables in your code during debugging sessions.
- Default: `true`
- Setting: `inlay_hints.show_value_hints`

**Options**

```json
{
  "inlay_hints": {
    "show_value_hints": false
  }
}
```

Inline value hints can also be toggled from the Editor Controls menu in the editor toolbar.

### Log Dap Communications

- Description: Whether to log messages between active debug adapters and Zed. (Used for DAP development)
- Default: false
- Setting: debugger.log_dap_communications

**Options**

`boolean` values

```json
{
  "debugger": {
    "log_dap_communications": true
  }
}
```

### Format Dap Log Messages

- Description: Whether to format DAP messages when adding them to the debug adapter logger. (Used for DAP development)
- Default: false
- Setting: debugger.format_dap_log_messages

**Options**

`boolean` values

```json
{
  "debugger": {
    "format_dap_log_messages": true
  }
}
```

### Customizing Debug Adapters

- Description: Custom program path and arguments to override how Zed launches a specific debug adapter.
- Default: Adapter-specific
- Setting: `dap.$ADAPTER.binary` and `dap.$ADAPTER.args`

You can pass `binary`, `args`, or both. `binary` should be a path to a _debug adapter_ (like `lldb-dap`) not a _debugger_ (like `lldb` itself). The `args` setting overrides any arguments that Zed would otherwise pass to the adapter.

```json
{
  "dap": {
    "CodeLLDB": {
      "binary": "/Users/name/bin/lldb-dap",
      "args": ["--wait-for-debugger"]
    }
  }
}
```

## Theme

The Debugger supports the following theme options:

- `debugger.accent`: Color used to accent breakpoint & breakpoint-related symbols
- `editor.debugger_active_line.background`: Background color of active debug line

## Troubleshooting

If you're running into problems with the debugger, please [open a GitHub issue](https://github.com/zed-industries/zed/issues/new?template=04_bug_debugger.yml) or [schedule an onboarding call](https://cal.com/team/zed-research/debugger) with us so we can help understand and fix your issue.

There are also some features you can use to gather more information about the problem:

- When you have a session running in the debug panel, you can run the {#action dev::CopyDebugAdapterArguments} action to copy a JSON blob to the clipboard that describes how Zed initialized the session. This is especially useful when the session failed to start, and is great context to add if you open a GitHub issue.
- You can also use the {#action dev::OpenDebugAdapterLogs} action to see a trace of all of Zed's communications with debug adapters during the most recent debug sessions.
