src/debugAdapter: add delve 'call' command support

Delve supports function calls. Even though it is still
experimental and can be applied only to a limited set
of functions, this is a useful feature, many vscode-go
users long for.

Unlike other javascript/typescript debuggers, delve
treats function calls specially and requires different
call paths than usual expression evaluation. That is
because Go is a compiled, runtime-managed GC language,
calling a function safely from debugger is complex.
DAP and VS Code UI does not distinguish function calls
and other expression evaluation either, so we have to
implement this in the same `evaluateRequest` context.

We use a heuristic to guess which route (call or
expression evaluation) we need to take based on
evaluateRequest's request.

The set of expressions delve supports includes some of
the builtin function calls like `len`, `cap`. We also
expect some grammar changes due to the ongoing effort for
Go2 experiment. In order to cope with this uncertainty,
this change requires users to specify their intention
using the 'call' keyword. Any expression that starts with
'call' and contains function-call-like strings, will cause
the evaluateRequest to take the path for the `call` command.

And, DAP and VSCode assumes all expressions return only
one result, but in Go, function call can return multiple
values. In this CL, we work around this sementic difference
by wrapping all the return values in one wrapper result
that has all return values as children. Users can expand
each value.

While we are here, this CL also adds a logic to handle the
interface type value. Previously, it was captured by the
default case that does not show the underlying type and value.
Interface types behave differently depending on the underlying
data type and value (e.g. nil error
so showing the underlying type/value upfront helps debugging
much easier. In particular, the 'error' type is commonly used
as the last return value of a function call and the program
control flow changes depending on whether the error is nil.
So, here we surface the underlying type and, if the underlying
type is invalid and the addr is 0 (nil error), present the
result as 'nil <error>'. This allows users to recognize the 'nil'
error value without extra value expansion.

Any error with an underlying type will be presented as
`<error(someUnderlyingType)>` and require the value expansion.

I see we can further improve this display value handling and
try to follow delve's data presentation as much as possible but
that is a bigger change and is beyond the scope of this CL.

This is based on

Fixes golang/vscode-go#100

Co-authored-by: Eugene Kulabuhov <>
Change-Id: I4e1e876ab1582b17fa2c7bf0b911f31ec348b484
Run-TryBot: Hyang-Ah Hana Kim <>
TryBot-Result: kokoro <>
Reviewed-by: Polina Sokolova <>
1 file changed
tree: 410a52dfd5fe6bf8688edda5896498416e4e5eba
  1. .editorconfig
  2. .github/
  3. .gitignore
  4. .prettierrc.json
  5. .vscode/
  6. .vscodeignore
  12. build/
  13. docs/
  14. images/
  15. languages/
  16. package-lock.json
  17. package.json
  18. snippets/
  19. src/
  20. syntaxes/
  21. test/
  22. third_party/
  23. tools/
  24. tsconfig.json
  25. tslint.json
  26. typings/
  27. webpack.config.js

Go for Visual Studio Code


This extension provides rich language support for the Go programming language in VS Code.

Take a look at the Changelog to learn about new features.

This is the new home for the VS Code Go extension. We just migrated from Microsoft/vscode-go. Learn more about our move on the Go blog.


Getting started

Welcome! Whether you are new to Go or an experienced Go developer, we hope this extension will fit your needs and enhance your development experience.

Install Go

Before you start coding, make sure that you have already installed Go, as explained in the Go installation guide.

If you are unsure whether you have installed Go, open the Command Palette in VS Code (Ctrl+Shift+P) and run the Go: Locate Configured Go Tools command. If the GOROOT output is empty, you are missing a Go installation. For help installing Go, ask a question on the #newbies Gophers Slack channel.

Set up your environment

Read about Go code organization to learn how to configure your environment. This extension works in both GOPATH and module modes. We suggest using modules, as they are quickly becoming the new standard in the Go community.

Here are some additional resources for learning about how to set up your Go project:

NOTE: If you are using modules, we recommend using the Go language server, which is explained below.

More advanced users may be interested in using different GOPATHs or Go versions per-project. You can learn about the different GOPATH manipulation options in the GOPATH documentation. Take a look at the other customization options as well.

Install the extension

If you haven't already done so, install and open Visual Studio Code. Navigate to the Extensions pane (Ctrl+Shift+X). Search for “Go” and install this extension (the publisher ID is golang.Go).

Activate the Go extension

To activate the extension, open any directory or workspace containing Go code.

You should immediately see a prompt in the bottom-right corner of your screen titled Analysis Tools Missing. This extension relies on a suite of command-line tools, which must be installed separately. Accept the prompt, or use the Go: Install/Update Tools command to pick which tools you would like to install.

If you see an error that looks like command Go: Install/Update Tools not found, it means that the extension has failed to activate and register its commands. Please uninstall and then reinstall the extension.

Start coding

You're ready to Go!

Be sure to learn more about the many features of this extension, as well as how to customize them. Take a look at Troubleshooting and Help for further guidance.

Support for Go modules

Go modules have added a lot of complexity to the way that most tools and features are built for Go. Some, but not all, features of this extension have been updated to work with Go modules. Some features may also be slower in module mode. The features documentation contains more specific details.

In general, we recommend using gopls, the official Go language server, if you are using modules. Read more below and in the gopls documentation.


This extension has a wide range of features, including Intellisense, code navigation, and code editing support. It also shows build, vet, and lint diagnostics as you work and provides enhanced support for testing and debugging your programs. For more detail, see the full feature breakdown.

In addition to integrated editing features, the extension also provides several commands for working with Go files. You can access any of these by opening the Command Palette (Ctrl+Shift+P) and typing in the name of the command. See the full list of commands provided by the extension.

The majority of the extension‘s functionality comes from command-line tools. If you’re experiencing an issue with a specific feature, you may want to investigate the underlying tool. You can do this by taking a look at the full list of tools used by this extension.


Debugging is a major feature offered by this extension. For a comprehensive overview of how to debug your Go programs, please see the debugging guide.


This extension needs no configuration; it works out of the box. However, you may wish to modify settings to adjust your experience.

Many of the features are configurable to your preference. A few common modifications are mentioned below, but take a look at the full list of settings for an overview.


A commonly customized feature is the linter, which is a tool used to provide coding style feedback and suggestions. By default, this extension uses the official golint.

However, you are welcome to use more advanced options like staticcheck, golangci-lint, or revive. This can be configured via the "go.lintTool" setting, and the different options are explained more thoroughly in the list of diagnostic tools.


Advanced users may want to set different GOPATHs for different projects or install the Go tools to a different GOPATH. This is possible and explained in the GOPATH documentation.

Language Server

In the default mode, the Go extension relies upon a suite of command-line tools. A new alternative is to use a single language server, which provides language features through the Language Server Protocol.

The Go team at Google has developed gopls, which is the official Go language server. It is currently in an alpha state and under active development.

gopls is recommended for projects that use Go modules.

To opt-in to the language server, set "go.useLanguageServer" to true in your settings. You should then be prompted to install gopls. If you are not prompted, you can install gopls manually by running the Go: Install/Update Tools command and selecting gopls.

For more information, see the gopls documentation.

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If you're having issues with this extension, please reach out to us by filing an issue or asking a question on the Gophers Slack. We hang out in the #vscode channel!

Take a look at and for additional guidance.

Preview version

If you'd like to get early access to new features and bug fixes, you can use the nightly build of this extension. Learn how to install it in by reading the Go Nightly documentation.


We welcome your contributions and thank you for working to improve the Go development experience in VS Code. If you would like to help work on the VS Code Go extension, please see our contribution guide. It explains how to build and run the extension locally, and it describes the process of sending a contribution.

Code of Conduct

This project follows the Go Community Code of Conduct. If you encounter an issue, please mail