slog: remove Attr.AppendValue

Attr.AppendValue was originally intended to be a convenient and more
efficient way of formatting Attr values. But there is no one clearly
right way to format them, and the efficiency argument doesn't
really hold water: AppendValue skips the redundant but cheap type
check that occurs in

	switch a.Kind() {
	case IntKind:
		... a.Int() ..

but then formats Times and Durations as strings instead of integers.

We keep it internally to help out in a couple of places, but overall
it's better if Handler implementations do their own value formatting.
For casual use, fmt.Sprint(a.Value()) is fine.

Change-Id: Ie265f1ee5daf5f8002bfc2b70f4bf461cb07a10b
Reviewed-on: https://go-review.googlesource.com/c/exp/+/430098
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

Author: jba

slog/attr.go

@@ -279,9 +279,9 @@ func (a1 Attr) Equal(a2 Attr) bool {
 	}
 }
 
-// AppendValue appends a text representation of the Attr's value to dst.
+// appendValue appends a text representation of the Attr's value to dst.
 // The value is formatted as with fmt.Sprint.
-func (a Attr) AppendValue(dst []byte) []byte {
+func (a Attr) appendValue(dst []byte) []byte {
 	switch a.Kind() {
 	case StringKind:
 		return append(dst, a.str()...)

slog/attr_safe.go

@@ -58,5 +58,5 @@ func (a Attr) String() string {
 		return a.str()
 	}
 	var buf []byte
-	return string(a.AppendValue(buf))
+	return string(a.appendValue(buf))
 }

slog/attr_unsafe.go

@@ -78,5 +78,5 @@ func (a Attr) String() string {
 		return s
 	}
 	var buf []byte
-	return string(a.AppendValue(buf))
+	return string(a.appendValue(buf))
 }

slog/text_handler.go

@@ -136,7 +136,7 @@ func (ap *textAppender) appendAttrValue(a Attr) error {
 		}
 		ap.appendString(fmt.Sprint(a.Value()))
 	default:
-		*ap.buf() = a.AppendValue(*ap.buf())
+		*ap.buf() = a.appendValue(*ap.buf())
 	}
 	return nil
 }