ref(promslog): dry out AllowedStyle Set(), rename style options var

- Renames the style options var to drop the `Flag` portion of it's name,
  since it's no longer used for a flag, but merely to house valid
options.
- drys out Set method for AllowedStyle by comparing provided flag
  against our valid options list using `slices.Contains()`, updates
method var name for the funcs to not double up on `s` usage for
potential confusion

Signed-off-by: TJ Hoplock <[email protected]>

Author: tjhop

promslog/slog.go

@@ -25,14 +25,15 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 )
 
 var (
 	LevelFlagOptions  = []string{"debug", "info", "warn", "error"}
 	FormatFlagOptions = []string{"logfmt", "json"}
-	StyleFlagOptions  = []string{"slog", "go-kit"}
+	StyleOptions      = []string{"slog", "go-kit"}
 
 	callerAddFunc             = false
 	defaultWriter             = os.Stderr
@@ -146,18 +147,21 @@ type AllowedStyle struct {
 	s string
 }
 
-func (s *AllowedStyle) String() string {
-	return s.s
+func (a *AllowedStyle) String() string {
+	return a.s
 }
 
-func (s *AllowedStyle) Set(style string) error {
-	switch style {
-	case "slog", "go-kit":
-		s.s = style
-	default:
-		return fmt.Errorf("unrecognized log style %q", s)
+// Set updates the value of the allowed logging style. Valid options are `slog`
+// (default), and `go-kit`. Note that while it is possible to call this method
+// and update the allowed logging style after creating a logger, it has no
+// effect; the last call to Set() prior to initializing a new logger is the
+// value that will be used for the lifetime of the logger.
+func (a *AllowedStyle) Set(style string) error {
+	if !slices.Contains(StyleOptions, style) {
+		return fmt.Errorf("unrecognized log style %s", style)
 	}
 
+	a.s = style
 	return nil
 }