1 files changed, 105 insertions, 0 deletions
diff --git a/src/reflect/visiblefields.go b/src/reflect/visiblefields.go
new file mode 100644
index 0000000..9375faa
--- /dev/null
+++ b/src/reflect/visiblefields.go
@@ -0,0 +1,105 @@
+// Copyright 2021 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 reflect
+
+// VisibleFields returns all the visible fields in t, which must be a
+// struct type. A field is defined as visible if it's accessible
+// directly with a FieldByName call. The returned fields include fields
+// inside anonymous struct members and unexported fields. They follow
+// the same order found in the struct, with anonymous fields followed
+// immediately by their promoted fields.
+//
+// For each element e of the returned slice, the corresponding field
+// can be retrieved from a value v of type t by calling v.FieldByIndex(e.Index).
+func VisibleFields(t Type) []StructField {
+	if t == nil {
+		panic("reflect: VisibleFields(nil)")
+	}
+	if t.Kind() != Struct {
+		panic("reflect.VisibleFields of non-struct type")
+	}
+	w := &visibleFieldsWalker{
+		byName:   make(map[string]int),
+		visiting: make(map[Type]bool),
+		fields:   make([]StructField, 0, t.NumField()),
+		index:    make([]int, 0, 2),
+	}
+	w.walk(t)
+	// Remove all the fields that have been hidden.
+	// Use an in-place removal that avoids copying in
+	// the common case that there are no hidden fields.
+	j := 0
+	for i := range w.fields {
+		f := &w.fields[i]
+		if f.Name == "" {
+			continue
+		}
+		if i != j {
+			// A field has been removed. We need to shuffle
+			// all the subsequent elements up.
+			w.fields[j] = *f
+		}
+		j++
+	}
+	return w.fields[:j]
+}
+
+type visibleFieldsWalker struct {
+	byName   map[string]int
+	visiting map[Type]bool
+	fields   []StructField
+	index    []int
+}
+
+// walk walks all the fields in the struct type t, visiting
+// fields in index preorder and appending them to w.fields
+// (this maintains the required ordering).
+// Fields that have been overridden have their
+// Name field cleared.
+func (w *visibleFieldsWalker) walk(t Type) {
+	if w.visiting[t] {
+		return
+	}
+	w.visiting[t] = true
+	for i := 0; i < t.NumField(); i++ {
+		f := t.Field(i)
+		w.index = append(w.index, i)
+		add := true
+		if oldIndex, ok := w.byName[f.Name]; ok {
+			old := &w.fields[oldIndex]
+			if len(w.index) == len(old.Index) {
+				// Fields with the same name at the same depth
+				// cancel one another out. Set the field name
+				// to empty to signify that has happened, and
+				// there's no need to add this field.
+				old.Name = ""
+				add = false
+			} else if len(w.index) < len(old.Index) {
+				// The old field loses because it's deeper than the new one.
+				old.Name = ""
+			} else {
+				// The old field wins because it's shallower than the new one.
+				add = false
+			}
+		}
+		if add {
+			// Copy the index so that it's not overwritten
+			// by the other appends.
+			f.Index = append([]int(nil), w.index...)
+			w.byName[f.Name] = len(w.fields)
+			w.fields = append(w.fields, f)
+		}
+		if f.Anonymous {
+			if f.Type.Kind() == Pointer {
+				f.Type = f.Type.Elem()
+			}
+			if f.Type.Kind() == Struct {
+				w.walk(f.Type)
+			}
+		}
+		w.index = w.index[:len(w.index)-1]
+	}
+	delete(w.visiting, t)
+}