proto: equate floating-point NaNs

Treating NaNs as inequal has benefits in mathmetical operations,
but is almost certainly never desired behavior in tests.
Making them equal allows us to document that Equal reports true
if the encoded bytes are also equal (under deterministic marshaling).

Change-Id: Id11c9c1681d8785bcc52f0f42064339194065649
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/186179
Reviewed-by: Damien Neil <dneil@google.com>

proto/equal.go

@@ -6,6 +6,7 @@ package proto
 
 import (
 	"bytes"
+	"math"
 	"reflect"
 
 	"google.golang.org/protobuf/internal/encoding/wire"
@@ -13,14 +14,16 @@ import (
 )
 
 // Equal reports whether two messages are equal.
+// If two messages marshal to the same bytes under deterministic serialization,
+// then Equal is guaranteed to report true.
 //
 // Two messages are equal if they belong to the same message descriptor,
 // have the same set of populated known and extension field values,
 // and the same set of unknown fields values.
 //
 // Scalar values are compared with the equivalent of the == operator in Go,
-// except bytes values which are compared using bytes.Equal.
-// Note that this means that floating point NaNs are considered inequal.
+// except bytes values which are compared using bytes.Equal and
+// floating point values which specially treat NaNs as equal.
 // Message values are compared by recursively calling Equal.
 // Lists are equal if each element value is also equal.
 // Maps are equal if they have the same set of keys, where the pair of values
@@ -104,6 +107,13 @@ func equalValue(fd pref.FieldDescriptor, x, y pref.Value) bool {
 		return equalMessage(x.Message(), y.Message())
 	case fd.Kind() == pref.BytesKind:
 		return bytes.Equal(x.Bytes(), y.Bytes())
+	case fd.Kind() == pref.FloatKind, fd.Kind() == pref.DoubleKind:
+		fx := x.Float()
+		fy := y.Float()
+		if math.IsNaN(fx) || math.IsNaN(fy) {
+			return math.IsNaN(fx) && math.IsNaN(fy)
+		}
+		return fx == fy
 	default:
 		return x.Interface() == y.Interface()
 	}

proto/equal_test.go

@@ -5,6 +5,7 @@
 package proto_test
 
 import (
+	"math"
 	"testing"
 
 	"google.golang.org/protobuf/internal/encoding/pack"
@@ -74,6 +75,14 @@ var inequalities = []struct{ a, b proto.Message }{
 		&testpb.TestAllTypes{OptionalDouble: proto.Float64(1)},
 		&testpb.TestAllTypes{OptionalDouble: proto.Float64(2)},
 	},
+	{
+		&testpb.TestAllTypes{OptionalFloat: proto.Float32(float32(math.NaN()))},
+		&testpb.TestAllTypes{OptionalFloat: proto.Float32(0)},
+	},
+	{
+		&testpb.TestAllTypes{OptionalDouble: proto.Float64(float64(math.NaN()))},
+		&testpb.TestAllTypes{OptionalDouble: proto.Float64(0)},
+	},
 	{
 		&testpb.TestAllTypes{OptionalBool: proto.Bool(true)},
 		&testpb.TestAllTypes{OptionalBool: proto.Bool(false)},