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// Copyright 2020, The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package value
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import (
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	"reflect"
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	"strconv"
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)
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var anyType = reflect.TypeOf((*interface{})(nil)).Elem()
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// TypeString is nearly identical to reflect.Type.String,
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// but has an additional option to specify that full type names be used.
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func TypeString(t reflect.Type, qualified bool) string {
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	return string(appendTypeName(nil, t, qualified, false))
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}
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func appendTypeName(b []byte, t reflect.Type, qualified, elideFunc bool) []byte {
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	// BUG: Go reflection provides no way to disambiguate two named types
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	// of the same name and within the same package,
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	// but declared within the namespace of different functions.
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	// Use the "any" alias instead of "interface{}" for better readability.
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	if t == anyType {
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		return append(b, "any"...)
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	}
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	// Named type.
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	if t.Name() != "" {
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		if qualified && t.PkgPath() != "" {
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			b = append(b, '"')
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			b = append(b, t.PkgPath()...)
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			b = append(b, '"')
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			b = append(b, '.')
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			b = append(b, t.Name()...)
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		} else {
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			b = append(b, t.String()...)
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		}
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		return b
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	}
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	// Unnamed type.
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	switch k := t.Kind(); k {
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	case reflect.Bool, reflect.String, reflect.UnsafePointer,
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		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
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		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
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		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
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		b = append(b, k.String()...)
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	case reflect.Chan:
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		if t.ChanDir() == reflect.RecvDir {
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			b = append(b, "<-"...)
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		}
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		b = append(b, "chan"...)
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		if t.ChanDir() == reflect.SendDir {
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			b = append(b, "<-"...)
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		}
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		b = append(b, ' ')
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		b = appendTypeName(b, t.Elem(), qualified, false)
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	case reflect.Func:
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		if !elideFunc {
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			b = append(b, "func"...)
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		}
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		b = append(b, '(')
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		for i := 0; i < t.NumIn(); i++ {
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			if i > 0 {
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				b = append(b, ", "...)
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			}
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			if i == t.NumIn()-1 && t.IsVariadic() {
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				b = append(b, "..."...)
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				b = appendTypeName(b, t.In(i).Elem(), qualified, false)
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			} else {
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				b = appendTypeName(b, t.In(i), qualified, false)
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			}
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		}
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		b = append(b, ')')
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		switch t.NumOut() {
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		case 0:
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			// Do nothing
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		case 1:
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			b = append(b, ' ')
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			b = appendTypeName(b, t.Out(0), qualified, false)
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		default:
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			b = append(b, " ("...)
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			for i := 0; i < t.NumOut(); i++ {
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				if i > 0 {
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					b = append(b, ", "...)
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				}
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				b = appendTypeName(b, t.Out(i), qualified, false)
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			}
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			b = append(b, ')')
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		}
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	case reflect.Struct:
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		b = append(b, "struct{ "...)
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		for i := 0; i < t.NumField(); i++ {
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			if i > 0 {
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				b = append(b, "; "...)
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			}
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			sf := t.Field(i)
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			if !sf.Anonymous {
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				if qualified && sf.PkgPath != "" {
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					b = append(b, '"')
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					b = append(b, sf.PkgPath...)
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					b = append(b, '"')
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					b = append(b, '.')
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				}
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				b = append(b, sf.Name...)
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				b = append(b, ' ')
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			}
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			b = appendTypeName(b, sf.Type, qualified, false)
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			if sf.Tag != "" {
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				b = append(b, ' ')
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				b = strconv.AppendQuote(b, string(sf.Tag))
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			}
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		}
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		if b[len(b)-1] == ' ' {
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			b = b[:len(b)-1]
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		} else {
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			b = append(b, ' ')
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		}
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		b = append(b, '}')
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	case reflect.Slice, reflect.Array:
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		b = append(b, '[')
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		if k == reflect.Array {
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			b = strconv.AppendUint(b, uint64(t.Len()), 10)
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		}
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		b = append(b, ']')
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		b = appendTypeName(b, t.Elem(), qualified, false)
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	case reflect.Map:
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		b = append(b, "map["...)
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		b = appendTypeName(b, t.Key(), qualified, false)
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		b = append(b, ']')
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		b = appendTypeName(b, t.Elem(), qualified, false)
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	case reflect.Ptr:
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		b = append(b, '*')
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		b = appendTypeName(b, t.Elem(), qualified, false)
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	case reflect.Interface:
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		b = append(b, "interface{ "...)
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		for i := 0; i < t.NumMethod(); i++ {
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			if i > 0 {
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				b = append(b, "; "...)
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			}
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			m := t.Method(i)
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			if qualified && m.PkgPath != "" {
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				b = append(b, '"')
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				b = append(b, m.PkgPath...)
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				b = append(b, '"')
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				b = append(b, '.')
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			}
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			b = append(b, m.Name...)
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			b = appendTypeName(b, m.Type, qualified, true)
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		}
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		if b[len(b)-1] == ' ' {
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			b = b[:len(b)-1]
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		} else {
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			b = append(b, ' ')
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		}
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		b = append(b, '}')
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	default:
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		panic("invalid kind: " + k.String())
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	}
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	return b
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}
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