attribute: add Value.String() and deprecate Emit; update usages

CHANGELOG.md

@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - Add `ByteSlice` and `ByteSliceValue` functions for new `BYTESLICE` attribute type in `go.opentelemetry.io/otel/attribute`. (#7948)
+- Add `String` method to `attribute.Value` in `go.opentelemetry.io/otel/attribute` implementing `fmt.Stringer`; deprecate `Emit` in favor of `String`; update `go.opentelemetry.io/otel/exporters/prometheus` to use `Value.String`. (#8154)
 
 ### Changed
 

attribute/key_test.go

@@ -52,79 +52,85 @@ func TestJSONValue(t *testing.T) {
 		string(data))
 }
 
-func TestEmit(t *testing.T) {
+func TestString(t *testing.T) {
 	for _, testcase := range []struct {
 		name string
 		v    attribute.Value
 		want string
 	}{
 		{
-			name: `test Key.Emit() can emit a string representing self.BOOL`,
+			name: `test Value.String() can emit a string representing self.BOOL`,
 			v:    attribute.BoolValue(true),
 			want: "true",
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.BOOLSLICE`,
+			name: `test Value.String() can emit a string representing self.BOOLSLICE`,
 			v:    attribute.BoolSliceValue([]bool{true, false, true}),
 			want: `[true false true]`,
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.INT64SLICE`,
+			name: `test Value.String() can emit a string representing self.INT64SLICE`,
 			v:    attribute.Int64SliceValue([]int64{1, 42}),
 			want: `[1,42]`,
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.INT64`,
+			name: `test Value.String() can emit a string representing self.INT64`,
 			v:    attribute.Int64Value(42),
 			want: "42",
 		},
 		{
-			name: `test Key.Emit() can representing an int value`,
+			name: `test Value.String() can represent an int value`,
 			v:    attribute.IntValue(7),
 			want: "7",
 		},
 		{
-			name: `test Key.Emit() can represent an []int value`,
+			name: `test Value.String() can represent an []int value`,
 			v:    attribute.IntSliceValue([]int{1, 2, 3}),
 			want: `[1,2,3]`,
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.FLOAT64SLICE`,
+			name: `test Value.String() can emit a string representing self.FLOAT64SLICE`,
 			v:    attribute.Float64SliceValue([]float64{1.0, 42.5}),
 			want: `[1,42.5]`,
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.FLOAT64`,
+			name: `test Value.String() can emit a string representing self.FLOAT64`,
 			v:    attribute.Float64Value(42.1),
 			want: "42.1",
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.STRING`,
+			name: `test Value.String() can emit a string representing self.STRING`,
 			v:    attribute.StringValue("foo"),
 			want: "foo",
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.STRINGSLICE`,
+			name: `test Value.String() can emit a string representing self.STRINGSLICE`,
 			v:    attribute.StringSliceValue([]string{"foo", "bar"}),
 			want: `["foo","bar"]`,
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.BYTESLICE`,
+			name: `test Value.String() can emit a string representing self.BYTESLICE`,
 			v:    attribute.ByteSliceValue([]byte("foo")),
 			want: "Zm9v",
 		},
 		{
-			name: `test Key.Emit() can emit a string representing self.EMPTY`,
+			name: `test Value.String() can emit a string representing self.EMPTY`,
 			v:    attribute.Value{},
 			want: "",
 		},
 	} {
 		t.Run(testcase.name, func(t *testing.T) {
-			// proto: func (v attribute.Value) Emit() string {
-			have := testcase.v.Emit()
+			have := testcase.v.String()
 			if have != testcase.want {
 				t.Errorf("Want: %s, but have: %s", testcase.want, have)
 			}
 		})
 	}
 }
+
+func TestEmitDeprecated(t *testing.T) {
+	v := attribute.StringValue("foo")
+	if v.Emit() != v.String() {
+		t.Errorf("Emit() should delegate to String(), got %q and %q", v.Emit(), v.String())
+	}
+}

attribute/value.go

@@ -268,8 +268,9 @@ func (v Value) AsInterface() any {
 	return unknownValueType{}
 }
 
-// Emit returns a string representation of Value's data.
-func (v Value) Emit() string {
+// String returns a string representation of Value's data.
+// It implements the [fmt.Stringer] interface.
+func (v Value) String() string {
 	switch v.Type() {
 	case BOOLSLICE:
 		return fmt.Sprint(v.asBoolSlice())
@@ -308,6 +309,13 @@ func (v Value) Emit() string {
 	}
 }
 
+// Emit returns a string representation of Value's data.
+//
+// Deprecated: Use [Value.String] instead.
+func (v Value) Emit() string {
+	return v.String()
+}
+
 // MarshalJSON returns the JSON encoding of the Value.
 func (v Value) MarshalJSON() ([]byte, error) {
 	var jsonVal struct {

exporters/prometheus/exporter.go

@@ -617,7 +617,7 @@ func getAttrs(attrs attribute.Set, labelNamer otlptranslator.LabelNamer) ([]stri
 		for itr.Next() {
 			kv := itr.Attribute()
 			keys = append(keys, string(kv.Key))
-			values = append(values, kv.Value.Emit())
+			values = append(values, kv.Value.String())
 		}
 	} else {
 		// It sanitizes invalid characters and handles duplicate keys
@@ -631,10 +631,10 @@ func getAttrs(attrs attribute.Set, labelNamer otlptranslator.LabelNamer) ([]stri
 				return nil, nil, err
 			}
 			if _, ok := keysMap[key]; !ok {
-				keysMap[key] = []string{kv.Value.Emit()}
+				keysMap[key] = []string{kv.Value.String()}
 			} else {
 				// if the sanitized key is a duplicate, append to the list of keys
-				keysMap[key] = append(keysMap[key], kv.Value.Emit())
+				keysMap[key] = append(keysMap[key], kv.Value.String())
 			}
 		}
 		for key, vals := range keysMap {
@@ -812,7 +812,7 @@ func attributesToLabels(attrs []attribute.KeyValue, labelNamer otlptranslator.La
 		if err != nil {
 			return nil, err
 		}
-		labels[name] = attr.Value.Emit()
+		labels[name] = attr.Value.String()
 	}
 	return labels, nil
 }