schemagen

Schemagen

Schemagen is a tool to generate effective implementation of Validateable interface for your types to reduce validation overhead to ZERO.

Whether you choose to use code generation or runtime reflection traversal, validation will work either way.

Using reflection is easier because it does not require any codegen setup, but it does introduce minor performance decrease.

Unless performance is top-priority and validation is indeed a bottleneck (usually it's not), I'd recommend sticking with the reflection - it makes your codebase simpler to maintain. Though I've tried to make this tool as painless to use as go allows =)

How to use

WIP: no stable version yet

Go 1.24+ (with tool directive)

go get -tool github.com/metafates/schema/cmd/schemagen@main

This will add a tool directive to your go.mod file

Then you can use it with go:generate directive (notice the go tool prefix)

//go:generate go tool schemagen -type Foo,Bar

type Foo struct {
    A required.NonZero[string]
    B optional.Negative[int]
}

type Bar map[string]MyStruct

Go 1.23 and earlier

See https://marcofranssen.nl/manage-go-tools-via-go-modules

Or:

go install github.com/metafates/schema/cmd/schemagen@main

Ensure that schemagen is in your $PATH:

which schemagen # should output something if everything is ok

Then you can use it with go:generate directive

//go:generate schemagen -type Foo,Bar

type Foo struct {
    A required.NonZero[string]
    B optional.Negative[int]
}

type Bar map[string]MyStruct

And call go generate as usual

go generate ./...

You should see the following files generated:

• Foo.schema.go
• Bar.schema.go

What does it do

It generates YOUR_TYPE.schema.gen file with Validate() error method for each type specified. Therefore validate.Validate(v any) error will call this method instead of reflection-based field traversal.

That's it! It will reduce validataion overhead to almost zero.