Show and edit option values laid out as in named.conf

Values with blocks (logging, controls, ...) are shown over several lines
with indentation, and edited that way: the editor grows with its content,
Tab indents, Enter keeps the indentation. With a draft open, option tables
show the draft's values.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/namedconf/printer.go

@@ -36,6 +36,24 @@ func Compact(items []Item) string {
 // CompactStmt returns the statement on a single line with its semicolon.
 func CompactStmt(s *Stmt) string { return Compact(s.Items) + ";" }
 
+// FormatValue returns an option's value laid out as named.conf writes it:
+// blocks over several lines, indented with tabs. Values without a block,
+// and values that don't parse, are returned as they are.
+func FormatValue(name, value string) string {
+	if !strings.Contains(value, "{") {
+		return value
+	}
+	st, err := ParseOptionValue(name, value)
+	if err != nil {
+		return value
+	}
+	out := strings.TrimSuffix(strings.TrimRight(FormatStmt(st, 0), "\n"), ";")
+	if rest, ok := strings.CutPrefix(out, st.Keyword()); ok {
+		return strings.TrimLeft(rest, " ")
+	}
+	return value
+}
+
 // QuoteString returns s as a named.conf quoted string.
 func QuoteString(s string) string {
 	var sb strings.Builder

internal/namedconf/printer_test.go

@@ -0,0 +1,18 @@
+package namedconf
+
+import "testing"
+
+func TestFormatValue(t *testing.T) {
+	for _, c := range []struct{ name, value, want string }{
+		{"logging", `{ channel c { file "/var/log/named/x.log" versions 3; print-time yes; }; category default { c; }; }`,
+			// A short inner block stays on one line, as in named.conf.
+			"{\n\tchannel c { file \"/var/log/named/x.log\" versions 3; print-time yes; };\n\tcategory default { c; };\n}"},
+		{"allow-query", `{ allowed_clients; }`, `{ allowed_clients; }`}, // short: unchanged
+		{"directory", `"/var/cache/bind"`, `"/var/cache/bind"`},
+		{"logging", `{ broken`, `{ broken`}, // unparsable: as it is
+	} {
+		if got := FormatValue(c.name, c.value); got != c.want {
+			t.Errorf("FormatValue(%s, %q) =\n%s\nwant\n%s", c.name, c.value, got, c.want)
+		}
+	}
+}