hugo/common/hreflect/helpers.go

// Copyright 2019 The Hugo Authors. All rights reserved.
// Some functions in this file (see comments) is based on the Go source code,
// copyright The Go Authors and  governed by a BSD-style license.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package hreflect contains reflect helpers.
package hreflect

import (
	"reflect"

	"github.com/gohugoio/hugo/common/types"
)

// IsTruthful returns whether in represents a truthful value.
// See IsTruthfulValue
func IsTruthful(in interface{}) bool {
	switch v := in.(type) {
	case reflect.Value:
		return IsTruthfulValue(v)
	default:
		return IsTruthfulValue(reflect.ValueOf(in))
	}

}

var zeroType = reflect.TypeOf((*types.Zeroer)(nil)).Elem()

// IsTruthfulValue returns whether the given value has a meaningful truth value.
// This is based on template.IsTrue in Go's stdlib, but also considers
// IsZero and any interface value will be unwrapped before it's considered
// for truthfulness.
//
// Based on:
// https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/exec.go#L306
func IsTruthfulValue(val reflect.Value) (truth bool) {
	val = indirectInterface(val)

	if !val.IsValid() {
		// Something like var x interface{}, never set. It's a form of nil.
		return
	}

	if val.Type().Implements(zeroType) {
		return !val.Interface().(types.Zeroer).IsZero()
	}

	switch val.Kind() {
	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
		truth = val.Len() > 0
	case reflect.Bool:
		truth = val.Bool()
	case reflect.Complex64, reflect.Complex128:
		truth = val.Complex() != 0
	case reflect.Chan, reflect.Func, reflect.Ptr, reflect.Interface:
		truth = !val.IsNil()
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		truth = val.Int() != 0
	case reflect.Float32, reflect.Float64:
		truth = val.Float() != 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		truth = val.Uint() != 0
	case reflect.Struct:
		truth = true // Struct values are always true.
	default:
		return
	}

	return
}

// Based on: https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/exec.go#L931
func indirectInterface(v reflect.Value) reflect.Value {
	if v.Kind() != reflect.Interface {
		return v
	}
	if v.IsNil() {
		return reflect.Value{}
	}
	return v.Elem()
}