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Diffstat (limited to 'tpl/internal/go_templates/fmtsort/sort.go')
-rw-r--r-- | tpl/internal/go_templates/fmtsort/sort.go | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/tpl/internal/go_templates/fmtsort/sort.go b/tpl/internal/go_templates/fmtsort/sort.go new file mode 100644 index 000000000..70a305a3a --- /dev/null +++ b/tpl/internal/go_templates/fmtsort/sort.go @@ -0,0 +1,216 @@ +// Copyright 2018 The Go 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 fmtsort provides a general stable ordering mechanism +// for maps, on behalf of the fmt and text/template packages. +// It is not guaranteed to be efficient and works only for types +// that are valid map keys. +package fmtsort + +import ( + "reflect" + "sort" +) + +// Note: Throughout this package we avoid calling reflect.Value.Interface as +// it is not always legal to do so and it's easier to avoid the issue than to face it. + +// SortedMap represents a map's keys and values. The keys and values are +// aligned in index order: Value[i] is the value in the map corresponding to Key[i]. +type SortedMap struct { + Key []reflect.Value + Value []reflect.Value +} + +func (o *SortedMap) Len() int { return len(o.Key) } +func (o *SortedMap) Less(i, j int) bool { return compare(o.Key[i], o.Key[j]) < 0 } +func (o *SortedMap) Swap(i, j int) { + o.Key[i], o.Key[j] = o.Key[j], o.Key[i] + o.Value[i], o.Value[j] = o.Value[j], o.Value[i] +} + +// Sort accepts a map and returns a SortedMap that has the same keys and +// values but in a stable sorted order according to the keys, modulo issues +// raised by unorderable key values such as NaNs. +// +// The ordering rules are more general than with Go's < operator: +// +// - when applicable, nil compares low +// - ints, floats, and strings order by < +// - NaN compares less than non-NaN floats +// - bool compares false before true +// - complex compares real, then imag +// - pointers compare by machine address +// - channel values compare by machine address +// - structs compare each field in turn +// - arrays compare each element in turn. +// Otherwise identical arrays compare by length. +// - interface values compare first by reflect.Type describing the concrete type +// and then by concrete value as described in the previous rules. +// +func Sort(mapValue reflect.Value) *SortedMap { + if mapValue.Type().Kind() != reflect.Map { + return nil + } + key := make([]reflect.Value, mapValue.Len()) + value := make([]reflect.Value, len(key)) + iter := mapValue.MapRange() + for i := 0; iter.Next(); i++ { + key[i] = iter.Key() + value[i] = iter.Value() + } + sorted := &SortedMap{ + Key: key, + Value: value, + } + sort.Stable(sorted) + return sorted +} + +// compare compares two values of the same type. It returns -1, 0, 1 +// according to whether a > b (1), a == b (0), or a < b (-1). +// If the types differ, it returns -1. +// See the comment on Sort for the comparison rules. +func compare(aVal, bVal reflect.Value) int { + aType, bType := aVal.Type(), bVal.Type() + if aType != bType { + return -1 // No good answer possible, but don't return 0: they're not equal. + } + switch aVal.Kind() { + case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: + a, b := aVal.Int(), bVal.Int() + switch { + case a < b: + return -1 + case a > b: + return 1 + default: + return 0 + } + case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: + a, b := aVal.Uint(), bVal.Uint() + switch { + case a < b: + return -1 + case a > b: + return 1 + default: + return 0 + } + case reflect.String: + a, b := aVal.String(), bVal.String() + switch { + case a < b: + return -1 + case a > b: + return 1 + default: + return 0 + } + case reflect.Float32, reflect.Float64: + return floatCompare(aVal.Float(), bVal.Float()) + case reflect.Complex64, reflect.Complex128: + a, b := aVal.Complex(), bVal.Complex() + if c := floatCompare(real(a), real(b)); c != 0 { + return c + } + return floatCompare(imag(a), imag(b)) + case reflect.Bool: + a, b := aVal.Bool(), bVal.Bool() + switch { + case a == b: + return 0 + case a: + return 1 + default: + return -1 + } + case reflect.Ptr: + a, b := aVal.Pointer(), bVal.Pointer() + switch { + case a < b: + return -1 + case a > b: + return 1 + default: + return 0 + } + case reflect.Chan: + if c, ok := nilCompare(aVal, bVal); ok { + return c + } + ap, bp := aVal.Pointer(), bVal.Pointer() + switch { + case ap < bp: + return -1 + case ap > bp: + return 1 + default: + return 0 + } + case reflect.Struct: + for i := 0; i < aVal.NumField(); i++ { + if c := compare(aVal.Field(i), bVal.Field(i)); c != 0 { + return c + } + } + return 0 + case reflect.Array: + for i := 0; i < aVal.Len(); i++ { + if c := compare(aVal.Index(i), bVal.Index(i)); c != 0 { + return c + } + } + return 0 + case reflect.Interface: + if c, ok := nilCompare(aVal, bVal); ok { + return c + } + c := compare(reflect.ValueOf(aVal.Elem().Type()), reflect.ValueOf(bVal.Elem().Type())) + if c != 0 { + return c + } + return compare(aVal.Elem(), bVal.Elem()) + default: + // Certain types cannot appear as keys (maps, funcs, slices), but be explicit. + panic("bad type in compare: " + aType.String()) + } +} + +// nilCompare checks whether either value is nil. If not, the boolean is false. +// If either value is nil, the boolean is true and the integer is the comparison +// value. The comparison is defined to be 0 if both are nil, otherwise the one +// nil value compares low. Both arguments must represent a chan, func, +// interface, map, pointer, or slice. +func nilCompare(aVal, bVal reflect.Value) (int, bool) { + if aVal.IsNil() { + if bVal.IsNil() { + return 0, true + } + return -1, true + } + if bVal.IsNil() { + return 1, true + } + return 0, false +} + +// floatCompare compares two floating-point values. NaNs compare low. +func floatCompare(a, b float64) int { + switch { + case isNaN(a): + return -1 // No good answer if b is a NaN so don't bother checking. + case isNaN(b): + return 1 + case a < b: + return -1 + case a > b: + return 1 + } + return 0 +} + +func isNaN(a float64) bool { + return a != a +} |