Metago documentation

Directives

Metago annotations use Go directive comments: //mgo: with no space. Gofmt preserves them and Go documentation hides them from rendered API docs.

Directive	Purpose
`//mgo:gen template [Target] [args]`	Render into the package `meta.go`.
`//mgo:inline template [Target] [args]`	Insert output in the source file.
`//mgo:end`	End an inline block; inserted automatically.
`//mgo:<namespace> [flags] [key=value]`	Attach metadata without generating code.

// mgo:gen is prose and is ignored because it contains a space.

Sidecar generation

//mgo:gen stringer
type Status string

All //mgo:gen directives in one package write to the same meta.go file.

Inline generation

//mgo:inline stringer
type Status string

After generation, output follows the symbol and ends at an automatically managed marker:

//mgo:inline stringer
type Status string

func (s Status) String() string { return string(s) }

//mgo:end

Later runs replace only this generated region. Inline templates can call imports; missing imports are added to the source file.

Anchored and standalone

A directive in a type, function, or method doc comment is anchored. Its target is inferred, so every token after the template name is an argument:

//mgo:gen get /posts/{postID} auth=required
func (p PostRoutes) Show() {}

A separated directive is standalone. Its first bare token can explicitly name a local or imported target:

type Status string

//mgo:inline stringer Status

Targets include User, BuildUser, Server.Serve, server.Server, and net/http.Client.Do. A first token beginning with / or containing { is always a positional argument.

Stack directives

Directives compose in source order:

//mgo:inline signals
//mgo:gen validator
//mgo:api owner=core
type AuthSignals struct {
    Email string `json:"sig_email"`
}

Property lines must follow generation lines within the same comment block.

Property namespaces

Any namespace besides gen, inline, and end attaches metadata to the nearest type, field, method, function, or interface method:

//mgo:api owner=core
type User struct {
    //mgo:validate required max=100
    Name string `json:"name"`
    Age int `json:"age"` //mgo:validate min=0 max=150
}

Repeated namespaces merge: flags are unioned and later values replace earlier ones. Read them with prop, props, propHas, and propExists.