go:generate is a directive in Go that is used to run arbitrary commands during the build process, and is often used for code generation. It triggers command execution by adding comments like //go:generate some-command-here to the Go source file. These commands are usually used to generate protocol buffers, mock interfaces, stringer methods, etc. 1. The command is run in the package directory; 2. You can include multiple go:generate instructions in a single file; 3. Go generate must be run manually and will not be automatically executed with the build. Using code generation reduces repetitive work and reduces the probability of errors, such as generating command templates for CLI applications. Best practices include: submitting generated code to version control; recording how to regenerate; using relative paths with caution; generating results for tests; and avoiding too many irrelevant commands placed on a single line. Directives are usually placed in source files related to the generated content, or centrally placed in generate.go files for management.
The go:generate directive in Go is used to run arbitrary commands during the build process—typically for code generation. It's a way to automate tasks that produce source code based on existing files, templates, or other inputs.
How Does go:generate Work?
You use it by placing a comment in a Go source file like this:
//go:generate some-command-here
This line tells the go generate tool to execute some-command-here . These commands are usually custom scripts or tools that generate boilerplate code, protocol buffers, stringer methods, mocks, or any kind of auto-generated content.
- The command runs in the package directory.
- You can have multiple
go:generatelines in one file. - You must run
go generatemanually—it does not run automatically when you build or install your project.
Why Use Code Generation in Go Projects?
Go's philosophy favors simplicity and readability, but there are cases where writing repetitive code isn't practical. Code generation helps reduce manual work and potential errors.
Some common reasons include:
- Generating mock interfaces for testing
- Creating string representations of enums (
stringer) - Building protocol buffer or Thrift stubs
- Producing HTML or SQL from templates or DSLs
For example, if you're building a CLI app with Cobra, you might use code generation to scaffold new commands without having to write all the boilerplate yourself.
Best Practices When Using go:generate
Here are a few tips to make sure your use of go:generate stays clean and helpful:
- Keep generated code checked in : This avoids forcing every contributor to run generators locally just to build the project.
- Document how to regenerate : Make it easy for others (or future you) to know what tools are needed and how to re-run the generation.
- Use relative paths carefully : Commands should be written so they work regardless of where the package is checked out.
- Test the output : Generated code should still be part of your test suite. Don't assume it's always correct.
Also, avoid putting too many unrelated commands in one go:generate line. If things get complex, consider using a script and calling that instead.
Where to Place the Directive
You can put the go:generate directive in any .go file in the package. Typically, people place them in files that logically relate to the generated code—like placing a go:generate line for mocks in a test file, or one for stringers in an enum definition file.
It's also common to create a dedicated file like generate.go just to hold these directives, especially when multiple commands are involved.
//go:generate stringer -type=MyEnum //go:generate mockgen -source=service.go -destination=mocks/service_mock.go
That way, anyone looking at the package can quickly see what needs to be generated without digging through multiple files.
Basically that's it.
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