decode,interp: Finish up nil value support

Update msgpack, bson and cbor to use it.

format/bson/bson.go

@@ -82,6 +82,7 @@ func decodeBSONDocument(d *decode.D) {
 						d.FieldU8("subtype")
 						d.FieldRawLen("value", int64(length)*8)
 					case elementTypeUndefined:
+						//deprecated
 					case elementTypeObjectID:
 						d.FieldRawLen("value", 12*8)
 					case elementTypeBoolean:
@@ -89,6 +90,7 @@ func decodeBSONDocument(d *decode.D) {
 					case elementTypeDatatime:
 						d.FieldS32("value")
 					case elementTypeNull:
+						d.FieldValueNil("value")
 					case elementTypeRegexp:
 						d.FieldUTF8Null("value")
 						d.FieldUTF8Null("options")

format/bson/testdata/test.fqtest

@@ -59,6 +59,7 @@ $ fq -d bson verbose /test.bson
 0x60|                                    0a         |            .   |      type: "null" (10) (Null value) 0x6c-0x6c.7 (1)
 0x60|                                       6e 75 6c|             nul|      name: "null" 0x6d-0x71.7 (5)
 0x70|6c 00                                          |l.              |
+    |                                               |                |      value: null 0x72-NA (0)
 0x70|      00|                                      |  .|            |  terminator: 0 (valid) 0x72-0x72.7 (1)
 $ fq -d bson torepr /test.bson
 {

format/cbor/cbor.go

@@ -218,7 +218,7 @@ func decodeCBORValue(d *decode.D) interface{} {
 			case shortCountSpecialTrue:
 				d.FieldValueBool("value", true)
 			case shortCountSpecialNull:
-				// TODO: null
+				d.FieldValueNil("value")
 			case shortCountSpecialUndefined:
 				// TODO: undefined
 			case 24:

format/msgpack/msgpack.go

@@ -100,7 +100,7 @@ func decodeMsgPackValue(d *decode.D) {
 			d.FieldUTF8("value", int(length))
 		}},
 		{r: [2]byte{0xc0, 0xc0}, s: scalar.S{Sym: "nil"}, d: func(d *decode.D) {
-			// TODO: fq has no good null type atm
+			d.FieldValueNil("value")
 		}},
 		{r: [2]byte{0xc1, 0xc1}, s: scalar.S{Sym: "never_used"}, d: func(d *decode.D) {
 			d.Fatalf("0xc1 never used")

format/msgpack/testdata/test.fqtest

@@ -84,6 +84,7 @@ $ fq -d msgpack v test.msgpack
 0x40|6c 6c                                          |ll              |
     |                                               |                |      value{}: 0x42-0x42.7 (1)
 0x40|      c0|                                      |  .|            |        type: "nil" (0xc0) 0x42-0x42.7 (1)
+    |                                               |                |        value: null 0x43-NA (0)
 $ fq -d msgpack torepr test.msgpack
 {
   "array": [

internal/gojqextra/totype.go

@@ -87,6 +87,7 @@ func ToInt(x interface{}) (int, bool) {
 	case gojq.JQValue:
 		return ToInt(x.JQValueToGoJQ())
 	default:
+		// nil and other should fail, "null | tonumber" in jq is an error
 		return 0, false
 	}
 }
@@ -112,6 +113,7 @@ func ToFloat(x interface{}) (float64, bool) {
 	case gojq.JQValue:
 		return ToFloat(x.JQValueToGoJQ())
 	default:
+		// nil and other should fail, "null | tonumber" in jq is an error
 		return 0.0, false
 	}
 }

pkg/decode/decode.go

@@ -653,6 +653,10 @@ func (d *D) FieldValueStr(name string, a string, sms ...scalar.Mapper) {
 	d.FieldScalarFn(name, func(_ scalar.S) (scalar.S, error) { return scalar.S{Actual: a}, nil }, sms...)
 }
 
+func (d *D) FieldValueNil(name string, sms ...scalar.Mapper) {
+	d.FieldScalarFn(name, func(_ scalar.S) (scalar.S, error) { return scalar.S{Actual: nil}, nil }, sms...)
+}
+
 func (d *D) FieldValueRaw(name string, a []byte, sms ...scalar.Mapper) {
 	d.FieldScalarFn(name, func(_ scalar.S) (scalar.S, error) {
 		return scalar.S{Actual: bitio.NewBufferFromBytes(a, -1)}, nil

pkg/interp/preview.go

@@ -33,6 +33,8 @@ func previewValue(v interface{}, df scalar.DisplayFormat) string {
 			return fmt.Sprintf("%q", vv[0:50]) + "..."
 		}
 		return fmt.Sprintf("%q", vv)
+	case nil:
+		return "null"
 	case *bitio.Buffer:
 		return "raw bits"
 	case *big.Int: