internal/rosa/azalea: refactor delimiter insertion, add test

internal/rosa/azalea/azalea.go

@@ -303,7 +303,7 @@ func (ScanError) Error() string {
 
 // Parse parses expressions from r.
 func Parse(r io.Reader) (e []any, err error) {
-	r, err = insertDelimiters(r)
+	r = insertDelimiters(r)
 	var p parser
 	p.s.Init(r)
 
@@ -349,7 +349,7 @@ func isIdentRune(ch rune, i int) bool {
 	}
 	return ch > 0 && ch < rune(len(idents)) && idents[ch]
 }
-func insertDelimiters(r io.Reader) (io.Reader, error) {
+func insertDelimiters(r io.Reader) io.Reader {
 	var s scanner.Scanner
 	s.Init(r)
 	s.Mode = scanner.ScanIdents |
@@ -361,44 +361,43 @@ func insertDelimiters(r io.Reader) (io.Reader, error) {
 	s.Whitespace = 0
 	s.IsIdentRune = isIdentRune
 
-	var buf strings.Builder
+	var b strings.Builder
 	nldelim := false
-	b := new(runeStack)
+	delim := new(runeStack)
 
 	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
 		switch tok {
 		case '{', '[':
 			nldelim = false
 			if tok == '{' {
-				b.Push(';')
+				delim.Push(';')
 			} else {
-				b.Push(',')
+				delim.Push(',')
 			}
-			buf.WriteRune(tok)
+			b.WriteRune(tok)
 		case scanner.String, scanner.RawString, scanner.Int, scanner.Ident:
-			buf.WriteString(s.TokenText())
+			b.WriteString(s.TokenText())
 			nldelim = true
 		case '+', ':', '=', ',', ';':
 			nldelim = false
-			buf.WriteRune(tok)
+			b.WriteRune(tok)
 		case '\n':
 			if nldelim {
-				buf.WriteRune(b.Peek())
+				b.WriteRune(delim.Peek())
 				nldelim = false
 			}
-			buf.WriteRune(tok)
 		case '}', ']':
 			if nldelim {
-				buf.WriteRune(b.Peek())
+				b.WriteRune(delim.Peek())
 			}
-			b.Pop()
+			delim.Pop()
 			nldelim = true
-			buf.WriteRune(tok)
+			b.WriteRune(tok)
 		default:
-			buf.WriteRune(tok)
+			b.WriteRune(tok)
 		}
 	}
-	return strings.NewReader(buf.String()), nil
+	return strings.NewReader(b.String())
 }
 
 type runeStack struct {