reflect: import visiblefields code and tests from upstream

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)
+}

src/reflect/visiblefields_test.go

@@ -0,0 +1,349 @@
+// 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_test
+
+import (
+	. "reflect"
+	"strings"
+	"testing"
+)
+
+type structField struct {
+	name  string
+	index []int
+}
+
+var fieldsTests = []struct {
+	testName string
+	val      any
+	expect   []structField
+}{{
+	testName: "SimpleStruct",
+	val: struct {
+		A int
+		B string
+		C bool
+	}{},
+	expect: []structField{{
+		name:  "A",
+		index: []int{0},
+	}, {
+		name:  "B",
+		index: []int{1},
+	}, {
+		name:  "C",
+		index: []int{2},
+	}},
+}, {
+	testName: "NonEmbeddedStructMember",
+	val: struct {
+		A struct {
+			X int
+		}
+	}{},
+	expect: []structField{{
+		name:  "A",
+		index: []int{0},
+	}},
+}, {
+	testName: "EmbeddedExportedStruct",
+	val: struct {
+		SFG
+	}{},
+	expect: []structField{{
+		name:  "SFG",
+		index: []int{0},
+	}, {
+		name:  "F",
+		index: []int{0, 0},
+	}, {
+		name:  "G",
+		index: []int{0, 1},
+	}},
+}, {
+	testName: "EmbeddedUnexportedStruct",
+	val: struct {
+		sFG
+	}{},
+	expect: []structField{{
+		name:  "sFG",
+		index: []int{0},
+	}, {
+		name:  "F",
+		index: []int{0, 0},
+	}, {
+		name:  "G",
+		index: []int{0, 1},
+	}},
+}, {
+	testName: "TwoEmbeddedStructsWithCancelingMembers",
+	val: struct {
+		SFG
+		SF
+	}{},
+	expect: []structField{{
+		name:  "SFG",
+		index: []int{0},
+	}, {
+		name:  "G",
+		index: []int{0, 1},
+	}, {
+		name:  "SF",
+		index: []int{1},
+	}},
+}, {
+	testName: "EmbeddedStructsWithSameFieldsAtDifferentDepths",
+	val: struct {
+		SFGH3
+		SG1
+		SFG2
+		SF2
+		L int
+	}{},
+	expect: []structField{{
+		name:  "SFGH3",
+		index: []int{0},
+	}, {
+		name:  "SFGH2",
+		index: []int{0, 0},
+	}, {
+		name:  "SFGH1",
+		index: []int{0, 0, 0},
+	}, {
+		name:  "SFGH",
+		index: []int{0, 0, 0, 0},
+	}, {
+		name:  "H",
+		index: []int{0, 0, 0, 0, 2},
+	}, {
+		name:  "SG1",
+		index: []int{1},
+	}, {
+		name:  "SG",
+		index: []int{1, 0},
+	}, {
+		name:  "G",
+		index: []int{1, 0, 0},
+	}, {
+		name:  "SFG2",
+		index: []int{2},
+	}, {
+		name:  "SFG1",
+		index: []int{2, 0},
+	}, {
+		name:  "SFG",
+		index: []int{2, 0, 0},
+	}, {
+		name:  "SF2",
+		index: []int{3},
+	}, {
+		name:  "SF1",
+		index: []int{3, 0},
+	}, {
+		name:  "SF",
+		index: []int{3, 0, 0},
+	}, {
+		name:  "L",
+		index: []int{4},
+	}},
+}, {
+	testName: "EmbeddedPointerStruct",
+	val: struct {
+		*SF
+	}{},
+	expect: []structField{{
+		name:  "SF",
+		index: []int{0},
+	}, {
+		name:  "F",
+		index: []int{0, 0},
+	}},
+}, {
+	testName: "EmbeddedNotAPointer",
+	val: struct {
+		M
+	}{},
+	expect: []structField{{
+		name:  "M",
+		index: []int{0},
+	}},
+}, {
+	testName: "RecursiveEmbedding",
+	val:      Rec1{},
+	expect: []structField{{
+		name:  "Rec2",
+		index: []int{0},
+	}, {
+		name:  "F",
+		index: []int{0, 0},
+	}, {
+		name:  "Rec1",
+		index: []int{0, 1},
+	}},
+}, {
+	testName: "RecursiveEmbedding2",
+	val:      Rec2{},
+	expect: []structField{{
+		name:  "F",
+		index: []int{0},
+	}, {
+		name:  "Rec1",
+		index: []int{1},
+	}, {
+		name:  "Rec2",
+		index: []int{1, 0},
+	}},
+}, {
+	testName: "RecursiveEmbedding3",
+	val:      RS3{},
+	expect: []structField{{
+		name:  "RS2",
+		index: []int{0},
+	}, {
+		name:  "RS1",
+		index: []int{1},
+	}, {
+		name:  "i",
+		index: []int{1, 0},
+	}},
+}}
+
+type SFG struct {
+	F int
+	G int
+}
+
+type SFG1 struct {
+	SFG
+}
+
+type SFG2 struct {
+	SFG1
+}
+
+type SFGH struct {
+	F int
+	G int
+	H int
+}
+
+type SFGH1 struct {
+	SFGH
+}
+
+type SFGH2 struct {
+	SFGH1
+}
+
+type SFGH3 struct {
+	SFGH2
+}
+
+type SF struct {
+	F int
+}
+
+type SF1 struct {
+	SF
+}
+
+type SF2 struct {
+	SF1
+}
+
+type SG struct {
+	G int
+}
+
+type SG1 struct {
+	SG
+}
+
+type sFG struct {
+	F int
+	G int
+}
+
+type RS1 struct {
+	i int
+}
+
+type RS2 struct {
+	RS1
+}
+
+type RS3 struct {
+	RS2
+	RS1
+}
+
+type M map[string]any
+
+type Rec1 struct {
+	*Rec2
+}
+
+type Rec2 struct {
+	F string
+	*Rec1
+}
+
+func TestFields(t *testing.T) {
+	for _, test := range fieldsTests {
+		test := test
+		t.Run(test.testName, func(t *testing.T) {
+			typ := TypeOf(test.val)
+			fields := VisibleFields(typ)
+			if got, want := len(fields), len(test.expect); got != want {
+				t.Fatalf("unexpected field count; got %d want %d", got, want)
+			}
+
+			for j, field := range fields {
+				expect := test.expect[j]
+				t.Logf("field %d: %s", j, expect.name)
+				gotField := typ.FieldByIndex(field.Index)
+				// Unfortunately, FieldByIndex does not return
+				// a field with the same index that we passed in,
+				// so we set it to the expected value so that
+				// it can be compared later with the result of FieldByName.
+				gotField.Index = field.Index
+				expectField := typ.FieldByIndex(expect.index)
+				// ditto.
+				expectField.Index = expect.index
+				if !DeepEqual(gotField, expectField) {
+					t.Fatalf("unexpected field result\ngot %#v\nwant %#v", gotField, expectField)
+				}
+
+				// Sanity check that we can actually access the field by the
+				// expected name.
+				gotField1, ok := typ.FieldByName(expect.name)
+				if !ok {
+					t.Fatalf("field %q not accessible by name", expect.name)
+				}
+				if !DeepEqual(gotField1, expectField) {
+					t.Fatalf("unexpected FieldByName result; got %#v want %#v", gotField1, expectField)
+				}
+			}
+		})
+	}
+}
+
+// Must not panic with nil embedded pointer.
+func TestFieldByIndexErr(t *testing.T) {
+	type A struct {
+		S string
+	}
+	type B struct {
+		*A
+	}
+	v := ValueOf(B{})
+	_, err := v.FieldByIndexErr([]int{0, 0})
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	if !strings.Contains(err.Error(), "embedded struct field A") {
+		t.Fatal(err)
+	}
+}