Fix #3: コメントを追加

cmd/dataxl/main.go

@@ -95,6 +95,9 @@ Notes:
 	}
 
 	var out []byte
+	// Use table as the common representation whenever either side is a
+	// spreadsheet-like format. Structured formats can then share the same
+	// flatten/restore path for CSV, TSV, and XLSX.
 	if isTabular(opt.from) && isTabular(opt.to) {
 		t, err := parseTable(input, opt.from, opt.sheet)
 		if err != nil {
@@ -366,6 +369,8 @@ func writeXLSX(t table, sheet string) ([]byte, error) {
 		}
 	}
 	if len(t.Header) > 0 {
+		// The generated workbook is meant for editing, so keep the header row
+		// visible and visually distinct.
 		end, _ := excelize.CoordinatesToCellName(len(t.Header), 1)
 		style, _ := f.NewStyle(&excelize.Style{Font: &excelize.Font{Bold: true}})
 		_ = f.SetCellStyle(sheet, "A1", end, style)
@@ -401,6 +406,7 @@ func valueToTable(value any) table {
 		}
 		flatRows = append(flatRows, flat)
 	}
+	// Stable column ordering keeps generated CSV/TSV/XLSX diffs predictable.
 	sort.Strings(header)
 	rows := make([][]string, 0, len(flatRows))
 	for _, flat := range flatRows {
@@ -418,6 +424,8 @@ func recordsFromValue(value any) []any {
 	case []any:
 		return v
 	case map[string]any:
+		// Common wrapper keys let TOML and object-shaped inputs represent a
+		// table without adding a format-specific flag.
 		for _, key := range []string{"rows", "records", "items"} {
 			if rows, ok := v[key].([]any); ok {
 				return rows
@@ -429,6 +437,8 @@ func recordsFromValue(value any) []any {
 	}
 }
 
+// flatten converts nested values into spreadsheet-safe column paths such as
+// user.name and items[0].sku.
 func flatten(prefix string, value any, out map[string]string) {
 	switch v := value.(type) {
 	case map[string]any:
@@ -485,6 +495,8 @@ func scalarString(value any) string {
 	}
 }
 
+// tableToRecords restores each row by interpreting header cells as path
+// expressions. Empty headers are ignored so spare spreadsheet columns are safe.
 func tableToRecords(t table) []map[string]any {
 	var records []map[string]any
 	for _, row := range t.Rows {
@@ -501,6 +513,8 @@ func tableToRecords(t table) []map[string]any {
 	return records
 }
 
+// parseCell keeps spreadsheet round trips useful while avoiding broad type
+// inference that could surprise users editing IDs or codes.
 func parseCell(s string) any {
 	s = strings.TrimSpace(s)
 	if s == "" {
@@ -523,6 +537,8 @@ func parseCell(s string) any {
 
 var pathTokenRE = regexp.MustCompile(`([^\.\[\]]+)|\[(\d+)\]`)
 
+// setPath creates maps and slices as needed for dotted and indexed header
+// paths. Invalid intermediate shapes are left unchanged instead of guessing.
 func setPath(root map[string]any, path string, value any) {
 	tokens := parsePath(path)
 	if len(tokens) == 0 {