render.go

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package render

import (
	"bytes"
	"fmt"
	"reflect"
	"sort"
	"strconv"
)

var builtinTypeMap = map[reflect.Kind]string{
	reflect.Bool:       "bool",
	reflect.Complex128: "complex128",
	reflect.Complex64:  "complex64",
	reflect.Float32:    "float32",
	reflect.Float64:    "float64",
	reflect.Int16:      "int16",
	reflect.Int32:      "int32",
	reflect.Int64:      "int64",
	reflect.Int8:       "int8",
	reflect.Int:        "int",
	reflect.String:     "string",
	reflect.Uint16:     "uint16",
	reflect.Uint32:     "uint32",
	reflect.Uint64:     "uint64",
	reflect.Uint8:      "uint8",
	reflect.Uint:       "uint",
	reflect.Uintptr:    "uintptr",
}

var builtinTypeSet = map[string]struct{}{}

func init() {
	for _, v := range builtinTypeMap {
		builtinTypeSet[v] = struct{}{}
	}
}

var typeOfString = reflect.TypeOf("")
var typeOfInt = reflect.TypeOf(int(1))
var typeOfUint = reflect.TypeOf(uint(1))
var typeOfFloat = reflect.TypeOf(10.1)

// Render converts a structure to a string representation. Unline the "%#v"
// format string, this resolves pointer types' contents in structs, maps, and
// slices/arrays and prints their field values.
func Render(v interface{}) string {
	buf := bytes.Buffer{}
	s := (*traverseState)(nil)
	s.render(&buf, 0, reflect.ValueOf(v), false)
	return buf.String()
}

// renderPointer is called to render a pointer value.
//
// This is overridable so that the test suite can have deterministic pointer
// values in its expectations.
var renderPointer = func(buf *bytes.Buffer, p uintptr) {
	fmt.Fprintf(buf, "0x%016x", p)
}

// traverseState is used to note and avoid recursion as struct members are being
// traversed.
//
// traverseState is allowed to be nil. Specifically, the root state is nil.
type traverseState struct {
	parent *traverseState
	ptr    uintptr
}

func (s *traverseState) forkFor(ptr uintptr) *traverseState {
	for cur := s; cur != nil; cur = cur.parent {
		if ptr == cur.ptr {
			return nil
		}
	}

	fs := &traverseState{
		parent: s,
		ptr:    ptr,
	}
	return fs
}

func (s *traverseState) render(buf *bytes.Buffer, ptrs int, v reflect.Value, implicit bool) {
	if v.Kind() == reflect.Invalid {
		buf.WriteString("nil")
		return
	}
	vt := v.Type()

	// If the type being rendered is a potentially recursive type (a type that
	// can contain itself as a member), we need to avoid recursion.
	//
	// If we've already seen this type before, mark that this is the case and
	// write a recursion placeholder instead of actually rendering it.
	//
	// If we haven't seen it before, fork our `seen` tracking so any higher-up
	// renderers will also render it at least once, then mark that we've seen it
	// to avoid recursing on lower layers.
	pe := uintptr(0)
	vk := vt.Kind()
	switch vk {
	case reflect.Ptr:
		// Since structs and arrays aren't pointers, they can't directly be
		// recursed, but they can contain pointers to themselves. Record their
		// pointer to avoid this.
		switch v.Elem().Kind() {
		case reflect.Struct, reflect.Array:
			pe = v.Pointer()
		}

	case reflect.Slice, reflect.Map:
		pe = v.Pointer()
	}
	if pe != 0 {
		s = s.forkFor(pe)
		if s == nil {
			buf.WriteString("<REC(")
			if !implicit {
				writeType(buf, ptrs, vt)
			}
			buf.WriteString(")>")
			return
		}
	}

	isAnon := func(t reflect.Type) bool {
		if t.Name() != "" {
			if _, ok := builtinTypeSet[t.Name()]; !ok {
				return false
			}
		}
		return t.Kind() != reflect.Interface
	}

	switch vk {
	case reflect.Struct:
		if !implicit {
			writeType(buf, ptrs, vt)
		}
		structAnon := vt.Name() == ""
		buf.WriteRune('{')
		for i := 0; i < vt.NumField(); i++ {
			if i > 0 {
				buf.WriteString(", ")
			}
			anon := structAnon && isAnon(vt.Field(i).Type)

			if !anon {
				buf.WriteString(vt.Field(i).Name)
				buf.WriteRune(':')
			}

			s.render(buf, 0, v.Field(i), anon)
		}
		buf.WriteRune('}')

	case reflect.Slice:
		if v.IsNil() {
			if !implicit {
				writeType(buf, ptrs, vt)
				buf.WriteString("(nil)")
			} else {
				buf.WriteString("nil")
			}
			return
		}
		fallthrough

	case reflect.Array:
		if !implicit {
			writeType(buf, ptrs, vt)
		}
		anon := vt.Name() == "" && isAnon(vt.Elem())
		buf.WriteString("{")
		for i := 0; i < v.Len(); i++ {
			if i > 0 {
				buf.WriteString(", ")
			}

			s.render(buf, 0, v.Index(i), anon)
		}
		buf.WriteRune('}')

	case reflect.Map:
		if !implicit {
			writeType(buf, ptrs, vt)
		}
		if v.IsNil() {
			buf.WriteString("(nil)")
		} else {
			buf.WriteString("{")

			mkeys := v.MapKeys()
			tryAndSortMapKeys(vt, mkeys)

			kt := vt.Key()
			keyAnon := typeOfString.ConvertibleTo(kt) || typeOfInt.ConvertibleTo(kt) || typeOfUint.ConvertibleTo(kt) || typeOfFloat.ConvertibleTo(kt)
			valAnon := vt.Name() == "" && isAnon(vt.Elem())
			for i, mk := range mkeys {
				if i > 0 {
					buf.WriteString(", ")
				}

				s.render(buf, 0, mk, keyAnon)
				buf.WriteString(":")
				s.render(buf, 0, v.MapIndex(mk), valAnon)
			}
			buf.WriteRune('}')
		}

	case reflect.Ptr:
		ptrs++
		fallthrough
	case reflect.Interface:
		if v.IsNil() {
			writeType(buf, ptrs, v.Type())
			buf.WriteString("(nil)")
		} else {
			s.render(buf, ptrs, v.Elem(), false)
		}

	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
		writeType(buf, ptrs, vt)
		buf.WriteRune('(')
		renderPointer(buf, v.Pointer())
		buf.WriteRune(')')

	default:
		tstr := vt.String()
		implicit = implicit || (ptrs == 0 && builtinTypeMap[vk] == tstr)
		if !implicit {
			writeType(buf, ptrs, vt)
			buf.WriteRune('(')
		}

		switch vk {
		case reflect.String:
			fmt.Fprintf(buf, "%q", v.String())
		case reflect.Bool:
			fmt.Fprintf(buf, "%v", v.Bool())

		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
			fmt.Fprintf(buf, "%d", v.Int())

		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
			fmt.Fprintf(buf, "%d", v.Uint())

		case reflect.Float32, reflect.Float64:
			fmt.Fprintf(buf, "%g", v.Float())

		case reflect.Complex64, reflect.Complex128:
			fmt.Fprintf(buf, "%g", v.Complex())
		}

		if !implicit {
			buf.WriteRune(')')
		}
	}
}

func writeType(buf *bytes.Buffer, ptrs int, t reflect.Type) {
	parens := ptrs > 0
	switch t.Kind() {
	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
		parens = true
	}

	if parens {
		buf.WriteRune('(')
		for i := 0; i < ptrs; i++ {
			buf.WriteRune('*')
		}
	}

	switch t.Kind() {
	case reflect.Ptr:
		if ptrs == 0 {
			// This pointer was referenced from within writeType (e.g., as part of
			// rendering a list), and so hasn't had its pointer asterisk accounted
			// for.
			buf.WriteRune('*')
		}
		writeType(buf, 0, t.Elem())

	case reflect.Interface:
		if n := t.Name(); n != "" {
			buf.WriteString(t.String())
		} else {
			buf.WriteString("interface{}")
		}

	case reflect.Array:
		buf.WriteRune('[')
		buf.WriteString(strconv.FormatInt(int64(t.Len()), 10))
		buf.WriteRune(']')
		writeType(buf, 0, t.Elem())

	case reflect.Slice:
		if t == reflect.SliceOf(t.Elem()) {
			buf.WriteString("[]")
			writeType(buf, 0, t.Elem())
		} else {
			// Custom slice type, use type name.
			buf.WriteString(t.String())
		}

	case reflect.Map:
		if t == reflect.MapOf(t.Key(), t.Elem()) {
			buf.WriteString("map[")
			writeType(buf, 0, t.Key())
			buf.WriteRune(']')
			writeType(buf, 0, t.Elem())
		} else {
			// Custom map type, use type name.
			buf.WriteString(t.String())
		}

	default:
		buf.WriteString(t.String())
	}

	if parens {
		buf.WriteRune(')')
	}
}

type cmpFn func(a, b reflect.Value) int

type sortableValueSlice struct {
	cmp      cmpFn
	elements []reflect.Value
}

func (s sortableValueSlice) Len() int {
	return len(s.elements)
}

func (s sortableValueSlice) Less(i, j int) bool {
	return s.cmp(s.elements[i], s.elements[j]) < 0
}

func (s sortableValueSlice) Swap(i, j int) {
	s.elements[i], s.elements[j] = s.elements[j], s.elements[i]
}

// cmpForType returns a cmpFn which sorts the data for some type t in the same
// order that a go-native map key is compared for equality.
func cmpForType(t reflect.Type) cmpFn {
	switch t.Kind() {
	case reflect.String:
		return func(av, bv reflect.Value) int {
			a, b := av.String(), bv.String()
			if a < b {
				return -1
			} else if a > b {
				return 1
			}
			return 0
		}

	case reflect.Bool:
		return func(av, bv reflect.Value) int {
			a, b := av.Bool(), bv.Bool()
			if !a && b {
				return -1
			} else if a && !b {
				return 1
			}
			return 0
		}

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return func(av, bv reflect.Value) int {
			a, b := av.Int(), bv.Int()
			if a < b {
				return -1
			} else if a > b {
				return 1
			}
			return 0
		}

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32,
		reflect.Uint64, reflect.Uintptr, reflect.UnsafePointer:
		return func(av, bv reflect.Value) int {
			a, b := av.Uint(), bv.Uint()
			if a < b {
				return -1
			} else if a > b {
				return 1
			}
			return 0
		}

	case reflect.Float32, reflect.Float64:
		return func(av, bv reflect.Value) int {
			a, b := av.Float(), bv.Float()
			if a < b {
				return -1
			} else if a > b {
				return 1
			}
			return 0
		}

	case reflect.Interface:
		return func(av, bv reflect.Value) int {
			a, b := av.InterfaceData(), bv.InterfaceData()
			if a[0] < b[0] {
				return -1
			} else if a[0] > b[0] {
				return 1
			}
			if a[1] < b[1] {
				return -1
			} else if a[1] > b[1] {
				return 1
			}
			return 0
		}

	case reflect.Complex64, reflect.Complex128:
		return func(av, bv reflect.Value) int {
			a, b := av.Complex(), bv.Complex()
			if real(a) < real(b) {
				return -1
			} else if real(a) > real(b) {
				return 1
			}
			if imag(a) < imag(b) {
				return -1
			} else if imag(a) > imag(b) {
				return 1
			}
			return 0
		}

	case reflect.Ptr, reflect.Chan:
		return func(av, bv reflect.Value) int {
			a, b := av.Pointer(), bv.Pointer()
			if a < b {
				return -1
			} else if a > b {
				return 1
			}
			return 0
		}

	case reflect.Struct:
		cmpLst := make([]cmpFn, t.NumField())
		for i := range cmpLst {
			cmpLst[i] = cmpForType(t.Field(i).Type)
		}
		return func(a, b reflect.Value) int {
			for i, cmp := range cmpLst {
				if rslt := cmp(a.Field(i), b.Field(i)); rslt != 0 {
					return rslt
				}
			}
			return 0
		}
	}

	return nil
}

func tryAndSortMapKeys(mt reflect.Type, k []reflect.Value) {
	if cmp := cmpForType(mt.Key()); cmp != nil {
		sort.Sort(sortableValueSlice{cmp, k})
	}
}