Add tea issues --fields, allow printing labels (#312)

generalize list printing with dynamic fields

refactor print.IssuesList to use tableFromItems()

preparatory refactor

print.IssuesList: allow printing labels

move formatters to formatters.go

expose more printable fields on issue

add generic flags.FieldsFlag

add fields flag to tea issues, tea ms issues

validate provided fields

add strict username, or formatted user fields

change default fields

tea issues -> replace updated with labels
tea ms issues -> replace author with labels, reorder

Validate provided fields

Co-authored-by: Norwin Roosen <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/312
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: 6543 <6543@obermui.de>
Co-Authored-By: Norwin <noerw@noreply.gitea.io>
Co-Committed-By: Norwin <noerw@noreply.gitea.io>

cmd/flags/flags.go

@@ -5,6 +5,11 @@
 package flags
 
 import (
+	"fmt"
+	"strings"
+
+	"code.gitea.io/tea/modules/utils"
+
 	"github.com/urfave/cli/v2"
 )
 
@@ -91,3 +96,30 @@ var IssuePRFlags = append([]cli.Flag{
 	&PaginationPageFlag,
 	&PaginationLimitFlag,
 }, AllDefaultFlags...)
+
+// FieldsFlag generates a flag selecting printable fields.
+// To retrieve the value, use GetFields()
+func FieldsFlag(availableFields, defaultFields []string) *cli.StringFlag {
+	return &cli.StringFlag{
+		Name:    "fields",
+		Aliases: []string{"f"},
+		Usage: fmt.Sprintf(`Comma-separated list of fields to print. Available values:
+			%s
+		`, strings.Join(availableFields, ",")),
+		Value: strings.Join(defaultFields, ","),
+	}
+}
+
+// GetFields parses the values provided in a fields flag, and
+// optionally validates against valid values.
+func GetFields(ctx *cli.Context, validFields []string) ([]string, error) {
+	selection := strings.Split(ctx.String("fields"), ",")
+	if validFields != nil {
+		for _, field := range selection {
+			if !utils.Contains(validFields, field) {
+				return nil, fmt.Errorf("Invalid field '%s'", field)
+			}
+		}
+	}
+	return selection, nil
+}