struct.go

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

package argmapper

import "reflect"

// Struct should be embedded into any struct where the parameters are
// populated. This lets argmapper differentiate between arguments
// where you want the full struct provided or fields within the struct.
//
// Example:
//
//   type MyParams {
//     argmapper.Struct
//
//     // A and B will be populated through injection.
//     A, B int
//   }
//
// If the embedded Struct was left out, argmapper would look for
// a full MyParams type to inject.
//
// Named Parameters
//
// By default, the field name is the name of the parameter. In the
// example above, MyParams expects parameters named "A" and "B", both of
// type int.
//
// Parameter names are case insensitive.
//
// Parameters can be renamed using a struct tag. The example below
// renames the field "A" to "B".
//
//   type MyParams {
//     argmapper.Struct
//
//     A int `argmapper:"B"`
//   }
//
// Typed Parameters
//
// A field in the struct can be marked as typed only using struct tags.
// The field name of a typed field is ignored and argmapper will match it
// to any matching type.
//
//   type MyParams {
//     argmapper.Struct
//
//     A int `argmapper:",typeOnly"`
//   }
//
// Note the comma before the "typeOnly" string. The comma is necessary
// so tell argmapper you're setting an option versus renaming a field.
type Struct struct {
	structInterface
}

// structInterface so that users can't just embed any struct{} type.
type structInterface interface {
	argmapperStruct()
}

// isStruct returns true if the given type is a struct that embeds our
// struct marker.
func isStruct(t reflect.Type) bool {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}

	if t.Kind() != reflect.Struct {
		return false
	}

	for i := 0; i < t.NumField(); i++ {
		if isStructField(t.Field(i)) {
			return true
		}
	}

	return false
}

// isStructField returns true if the given struct field is our struct marker.
func isStructField(f reflect.StructField) bool {
	return f.Anonymous && f.Type == structMarkerType
}

var structMarkerType = reflect.TypeOf((*Struct)(nil)).Elem()