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Swift lldb

To debug Swift files, you can use the lldb-dap DAP server.

Let’s debug the following Sources/main.swift file:

// The Swift Programming Language
// https://docs.swift.org/swift-book

var user = "word";
print("Hello, " + user + "!")

Set Breakpoint

Configure DAP server

  1. Install Swift. Please see the Getting Started Guide on Swift.org for details on how to install Swift on your system. This installation will install the lldb-dap DAP server.

  2. After the installation, you should have the lldb-dap command available (make sure to close and reopen your IDE to ensure the lldb-dap command is properly recognized).

If you open a terminal and run the following command:

lldb-dap -help

You should see some instructions how to start lldb-dap server.

  1. Create a DAP Run/Debug configuration:

    DAP Configuration Type

  2. In the Server tab, click on create a new server:

    Create a new server

  3. It opens a new dialog to create DAP server, select Swift lldb template: Select Template

  4. After clicking on OK button, it will select the new server and pre-fill configurations:

Select New server

This will automatically populate:

  • the server name
  • the command which starts the DAP server which should look like this:
lldb-dap

This command will start the DAP server with stdio mode. You could start the server in socket mode with the following command:

lldb-dap -p ${port}
  1. Enable DAP server traces

If you wish to show DAP request/response traces when you will debug:

Show DAP traces

you need to select Trace with verbose.

Set verbose traces

Configure file mappings

To allows settings breakpoints to Swift files, you need configure mappings in the Mappings tab. As you have selected Swift lldb server, it will automatically populate the file mappings like this:

File mappings

Configure the executable file to run/debug

To debug swift files, you will need to build an executable. You can do that with

swift build

This command should generate an executable according your swift project settings:

File mappings

  1. Fill in the Configuration tab:
  • the working directory (usually the project's root directory)
  • the path to the executable file.

DAP Configuration/Configuration

  1. Select Launch as Debug mode.
  2. The DAP parameters of the launch should look like this:
{
  "type": "swift-lldb",
  "name": "Launch Swift executable",
  "request": "launch",
  "program": "${file}",
  "cwd": "${workspaceFolder}"
}

When the run configuration starts:

  • ${workspaceFolder} will be replaced with the working directory you specified.
  • ${file} will be replaced with the full path to your executable.

Set Breakpoint

After applying the run configuration, you should set a breakpoint to files which matches file mappings. Set a breakpoint in the Sources/main.swift file:

Set Breakpoint

Debugging

You can start the run configuration in either Run or Debug mode. Once started, you should see DAP traces in the console:

You will also see Threads and Variables:

Debugging / Threads

Language Support

If you need language support for Swift (completion, validation, etc) you can configure the SourceKit-LSP Language Server