log/slog: use Infinity instead of Inf

JSON is derived from Javascript, so we should use Javascript-inspired
literals instead of ones more common to Go.

In Javascript, infinity is declared as Infinity rather than Inf.

Change-Id: I6c81353d0c677640f3f11961a37d792408ac03fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/478758
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/log/slog/json_handler.go

@@ -79,7 +79,7 @@ func (h *JSONHandler) WithGroup(name string) Handler {
 // Values are formatted as with encoding/json.Marshal, with the following
 // exceptions:
 //   - Floating-point NaNs and infinities are formatted as one of the strings
-//     "NaN", "+Inf" or "-Inf".
+//     "NaN", "Infinity" or "-Infinity".
 //   - Levels are formatted as with Level.String.
 //   - HTML characters are not escaped.
 //
@@ -113,9 +113,9 @@ func appendJSONValue(s *handleState, v Value) error {
 		// json.Marshal fails on special floats, so handle them here.
 		switch {
 		case math.IsInf(f, 1):
-			s.buf.WriteString(`"+Inf"`)
+			s.buf.WriteString(`"Infinity"`)
 		case math.IsInf(f, -1):
-			s.buf.WriteString(`"-Inf"`)
+			s.buf.WriteString(`"-Infinity"`)
 		case math.IsNaN(f):
 			s.buf.WriteString(`"NaN"`)
 		default:

src/log/slog/json_handler_test.go

@@ -111,8 +111,8 @@ func TestJSONAppendAttrValueSpecial(t *testing.T) {
 		want  string
 	}{
 		{math.NaN(), `"NaN"`},
-		{math.Inf(+1), `"+Inf"`},
-		{math.Inf(-1), `"-Inf"`},
+		{math.Inf(+1), `"Infinity"`},
+		{math.Inf(-1), `"-Infinity"`},
 		{LevelWarn, `"WARN"`},
 	} {
 		got := jsonValueString(t, AnyValue(test.value))