stringer.go

package pretty

import (
	"fmt"
	"reflect"

	"github.com/pierrre/go-libs/reflectutil"
	"github.com/pierrre/pretty/internal/itfassert"
)

var stringerImplementsCache = reflectutil.NewImplementsCacheFor[fmt.Stringer]()

// StringerWriter is a [ValueWriter] that handles [fmt.Stringer].
//
// If [fmt.Stringer.String] panics, [StringerWriter.WriteValue] returns false.
//
// It should be created with [NewStringerWriter].
type StringerWriter struct {
	// ShowLen shows the len.
	// Default: false.
	ShowLen bool
	// Quote quotes the string.
	// Default: true.
	Quote bool
	// MaxLen is the maximum length of the string.
	// Default: 0 (no limit).
	MaxLen int
}

// NewStringerWriter creates a new [StringerWriter].
func NewStringerWriter() *StringerWriter {
	return &StringerWriter{
		ShowLen: false,
		Quote:   true,
		MaxLen:  0,
	}
}

// WriteValue implements [ValueWriter].
func (vw *StringerWriter) WriteValue(st *State, v reflect.Value) bool {
	typ := v.Type()
	if typ == reflectValueType {
		return false
	}
	if !stringerImplementsCache.ImplementedBy(typ) {
		return false
	}
	sr, ok := itfassert.Assert[fmt.Stringer](v)
	if !ok {
		return false
	}
	s, ok := func() (_ string, ok bool) {
		defer func() {
			if !ok {
				_ = recover()
			}
		}()
		return sr.String(), true
	}()
	if !ok {
		return false
	}
	writeArrowWrappedString(st, "String() ")
	writeStringValue(st, s, vw.ShowLen, false, 0, vw.Quote, vw.MaxLen)
	return true
}

// Supports implements [SupportChecker].
func (vw *StringerWriter) Supports(typ reflect.Type) ValueWriter {
	var res ValueWriter
	if typ != reflectValueType && stringerImplementsCache.ImplementedBy(typ) {
		res = vw
	}
	return res
}