fix: json/encoding marshal errors of parameters with optional structs

Generated parameter structs have field tags omitempty and/or omitzero annotations:
* omitempty for slices, maps and non-optional nullable fields
* omitempty and omitzero for optional nullable fields
* nothing for other fields

Author: maelick

gen/_template/parameters.tmpl

@@ -19,7 +19,7 @@
 type {{ $op.Name }}Params struct {
 {{- range $p := $op.Params }}
 	{{- template "godoc" $p.GoDoc }}
-	{{ $p.Name }} {{ $p.Type.Go }}
+	{{ $p.Name }} {{ $p.Type.Go }} {{ if $p.GoStructTag }}{{ backquote $p.GoStructTag }}{{ end }}
 {{- end }}
 }
 

gen/ir/operation.go

@@ -122,6 +122,31 @@ func (op Parameter) GoDoc() []string {
 	return prettyDoc(s.Description, notice)
 }
 
+// GoStructTag returns a Go struct tag for this parameter (if relevant).
+// Currently only returns emoempty of arrays, maps and nullable Type.GenericVariant,
+// and omitzero for parameters with optional Type.GenericVariant
+func (op Parameter) GoStructTag() string {
+	if op.Type == nil {
+		return ""
+	}
+	switch op.Type.Kind {
+	case KindArray, KindMap:
+		return `json:",omitempty"`
+	default:
+		return op.goStructTag()
+	}
+}
+
+func (op Parameter) goStructTag() string {
+	variant := op.Type.GenericVariant
+	if variant.OnlyNullable() {
+		return `json:",omitempty"`
+	} else if variant.Optional {
+		return `json:",omitempty,omitzero"`
+	}
+	return ""
+}
+
 // Default returns default value of this field, if it is set.
 func (op Parameter) Default() Default {
 	var schema *jsonschema.Schema

go.mod

@@ -1,8 +1,8 @@
 module github.com/ogen-go/ogen
 
-go 1.23.0
+go 1.24.0
 
-toolchain go1.23.7
+toolchain go1.24.1
 
 require (
 	github.com/davecgh/go-spew v1.1.1