1 files changed, 239 insertions, 0 deletions
diff --git a/src/reflect/deepequal.go b/src/reflect/deepequal.go
new file mode 100644
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--- /dev/null
+++ b/src/reflect/deepequal.go
@@ -0,0 +1,239 @@
+// Copyright 2009 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.
+
+// Deep equality test via reflection
+
+package reflect
+
+import (
+	"internal/bytealg"
+	"unsafe"
+)
+
+// During deepValueEqual, must keep track of checks that are
+// in progress. The comparison algorithm assumes that all
+// checks in progress are true when it reencounters them.
+// Visited comparisons are stored in a map indexed by visit.
+type visit struct {
+	a1  unsafe.Pointer
+	a2  unsafe.Pointer
+	typ Type
+}
+
+// Tests for deep equality using reflected types. The map argument tracks
+// comparisons that have already been seen, which allows short circuiting on
+// recursive types.
+func deepValueEqual(v1, v2 Value, visited map[visit]bool) bool {
+	if !v1.IsValid() || !v2.IsValid() {
+		return v1.IsValid() == v2.IsValid()
+	}
+	if v1.Type() != v2.Type() {
+		return false
+	}
+
+	// We want to avoid putting more in the visited map than we need to.
+	// For any possible reference cycle that might be encountered,
+	// hard(v1, v2) needs to return true for at least one of the types in the cycle,
+	// and it's safe and valid to get Value's internal pointer.
+	hard := func(v1, v2 Value) bool {
+		switch v1.Kind() {
+		case Pointer:
+			if v1.typ().PtrBytes == 0 {
+				// not-in-heap pointers can't be cyclic.
+				// At least, all of our current uses of runtime/internal/sys.NotInHeap
+				// have that property. The runtime ones aren't cyclic (and we don't use
+				// DeepEqual on them anyway), and the cgo-generated ones are
+				// all empty structs.
+				return false
+			}
+			fallthrough
+		case Map, Slice, Interface:
+			// Nil pointers cannot be cyclic. Avoid putting them in the visited map.
+			return !v1.IsNil() && !v2.IsNil()
+		}
+		return false
+	}
+
+	if hard(v1, v2) {
+		// For a Pointer or Map value, we need to check flagIndir,
+		// which we do by calling the pointer method.
+		// For Slice or Interface, flagIndir is always set,
+		// and using v.ptr suffices.
+		ptrval := func(v Value) unsafe.Pointer {
+			switch v.Kind() {
+			case Pointer, Map:
+				return v.pointer()
+			default:
+				return v.ptr
+			}
+		}
+		addr1 := ptrval(v1)
+		addr2 := ptrval(v2)
+		if uintptr(addr1) > uintptr(addr2) {
+			// Canonicalize order to reduce number of entries in visited.
+			// Assumes non-moving garbage collector.
+			addr1, addr2 = addr2, addr1
+		}
+
+		// Short circuit if references are already seen.
+		typ := v1.Type()
+		v := visit{addr1, addr2, typ}
+		if visited[v] {
+			return true
+		}
+
+		// Remember for later.
+		visited[v] = true
+	}
+
+	switch v1.Kind() {
+	case Array:
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Slice:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.UnsafePointer() == v2.UnsafePointer() {
+			return true
+		}
+		// Special case for []byte, which is common.
+		if v1.Type().Elem().Kind() == Uint8 {
+			return bytealg.Equal(v1.Bytes(), v2.Bytes())
+		}
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Interface:
+		if v1.IsNil() || v2.IsNil() {
+			return v1.IsNil() == v2.IsNil()
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Pointer:
+		if v1.UnsafePointer() == v2.UnsafePointer() {
+			return true
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Struct:
+		for i, n := 0, v1.NumField(); i < n; i++ {
+			if !deepValueEqual(v1.Field(i), v2.Field(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Map:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.UnsafePointer() == v2.UnsafePointer() {
+			return true
+		}
+		iter := v1.MapRange()
+		for iter.Next() {
+			val1 := iter.Value()
+			val2 := v2.MapIndex(iter.Key())
+			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
+				return false
+			}
+		}
+		return true
+	case Func:
+		if v1.IsNil() && v2.IsNil() {
+			return true
+		}
+		// Can't do better than this:
+		return false
+	case Int, Int8, Int16, Int32, Int64:
+		return v1.Int() == v2.Int()
+	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
+		return v1.Uint() == v2.Uint()
+	case String:
+		return v1.String() == v2.String()
+	case Bool:
+		return v1.Bool() == v2.Bool()
+	case Float32, Float64:
+		return v1.Float() == v2.Float()
+	case Complex64, Complex128:
+		return v1.Complex() == v2.Complex()
+	default:
+		// Normal equality suffices
+		return valueInterface(v1, false) == valueInterface(v2, false)
+	}
+}
+
+// DeepEqual reports whether x and y are “deeply equal,” defined as follows.
+// Two values of identical type are deeply equal if one of the following cases applies.
+// Values of distinct types are never deeply equal.
+//
+// Array values are deeply equal when their corresponding elements are deeply equal.
+//
+// Struct values are deeply equal if their corresponding fields,
+// both exported and unexported, are deeply equal.
+//
+// Func values are deeply equal if both are nil; otherwise they are not deeply equal.
+//
+// Interface values are deeply equal if they hold deeply equal concrete values.
+//
+// Map values are deeply equal when all of the following are true:
+// they are both nil or both non-nil, they have the same length,
+// and either they are the same map object or their corresponding keys
+// (matched using Go equality) map to deeply equal values.
+//
+// Pointer values are deeply equal if they are equal using Go's == operator
+// or if they point to deeply equal values.
+//
+// Slice values are deeply equal when all of the following are true:
+// they are both nil or both non-nil, they have the same length,
+// and either they point to the same initial entry of the same underlying array
+// (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal.
+// Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil))
+// are not deeply equal.
+//
+// Other values - numbers, bools, strings, and channels - are deeply equal
+// if they are equal using Go's == operator.
+//
+// In general DeepEqual is a recursive relaxation of Go's == operator.
+// However, this idea is impossible to implement without some inconsistency.
+// Specifically, it is possible for a value to be unequal to itself,
+// either because it is of func type (uncomparable in general)
+// or because it is a floating-point NaN value (not equal to itself in floating-point comparison),
+// or because it is an array, struct, or interface containing
+// such a value.
+// On the other hand, pointer values are always equal to themselves,
+// even if they point at or contain such problematic values,
+// because they compare equal using Go's == operator, and that
+// is a sufficient condition to be deeply equal, regardless of content.
+// DeepEqual has been defined so that the same short-cut applies
+// to slices and maps: if x and y are the same slice or the same map,
+// they are deeply equal regardless of content.
+//
+// As DeepEqual traverses the data values it may find a cycle. The
+// second and subsequent times that DeepEqual compares two pointer
+// values that have been compared before, it treats the values as
+// equal rather than examining the values to which they point.
+// This ensures that DeepEqual terminates.
+func DeepEqual(x, y any) bool {
+	if x == nil || y == nil {
+		return x == y
+	}
+	v1 := ValueOf(x)
+	v2 := ValueOf(y)
+	if v1.Type() != v2.Type() {
+		return false
+	}
+	return deepValueEqual(v1, v2, make(map[visit]bool))
+}